Omron PLC Error Codes

80F1: Memory error

What it means: The CPU found a checksum error or fault in its stored data (user program, PLC Setup or other settings) and stopped the program.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit, Memory Error Flag A401.15 ON

Likely causes

• Power was turned off while the user program was being backed up to flash or backup memory
• Corrupted PLC Setup or routing table data
• Automatic transfer from the Memory Cassette at startup failed because the needed files are missing or the cassette is not fitted (CP1L, CP1H)
• Flash or backup memory hardware fault in the CPU Unit

First checks, in this order

1. Read A403 to see where the error is: A403.00 user program and A403.04 PLC Setup (all three models); A403.07 routing tables and A403.09 Memory Cassette read at startup (CP1L, CP1H); A403.08 CPU Bus Unit Setup (CP1H); A403.10 flash or backup memory (CP1E, CP1L).
2. A403.00 ON: transfer the user program again with CX-Programmer. A403.04 ON: transfer the PLC Setup again. A403.07 ON: transfer the routing tables again.
3. If the startup transfer failed, put the required files on the Memory Cassette and make sure it is installed.
4. A403.10 ON points to a CPU hardware problem: replace the CPU Unit.
5. On a CP1H the 7-segment display shows 80, F1, then the location, for example 00 01 user program, 00 10 PLC Setup, 00 80 routing tables, 01 00 CPU Bus Unit Setup, 02 00 Memory Cassette transfer at startup.

80F1: Memory Error

What it means: A memory error or checksum error was found in the CPU Unit memory; if automatic recovery from the built-in flash memory is not possible, operation stops.^[4][6]

PLC response: CPU stops, RUN off, ERR/ALM lit, Memory Error Flag A401.15 ON

Likely causes

• Power was turned off while data was being written to the built-in flash (backup) memory
• Checksum error in the user program, PLC Setup, registered I/O tables, routing tables or CPU Bus Unit Setup
• Electrical noise or a conductive object inside the Unit
• Memory element or memory circuit failure; Omron also notes SRAM data can be corrupted by cosmic rays or natural radiation

First checks, in this order

1. Read A403: A403.00 user program, A403.04 PLC Setup, A403.05 registered I/O tables, A403.07 routing tables, A403.08 CPU Bus Unit Setup.
2. Transfer the affected data again with CX-Programmer, or from a Memory Card using automatic transfer at startup or simple backup.
3. Restart the CPU Unit: data is reloaded from the built-in flash memory, which sometimes clears the error.
4. If it keeps returning, look for conductive debris and noise paths (FG, power lines), then replace the CPU Unit.

00F7: Battery error

What it means: Battery error detection is switched on in the PLC Setup and the CPU battery voltage is low or the battery is missing; the program keeps running.^[1][2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing, Battery Error Flag A402.04 ON

Likely causes

• Battery voltage low
• Battery not fitted or its connector loose
• Battery-free operation used while battery error detection is still enabled

First checks, in this order

1. Check the battery connection, then replace the battery if the voltage is low.
2. If the machine runs without a battery on purpose, select Do not detect battery error in the PLC Setup.
3. A low battery can make held memory (DM, Holding and Counter areas) unstable at the next power-up: use the Battery Error Flag A402.04 in the program to stop outputs that depend on that data.
4. On a CP1H the display shows 00 F7.

00F7: Battery Error

What it means: The PLC Setup is set to detect battery errors and the CPU backup battery is missing or its voltage has dropped.^[4][6]

PLC response: Operation continues, RUN lit, ERR/ALM flashing, A402.04 ON

Likely causes

• Battery voltage low (battery at end of life)
• Battery connector disconnected

First checks, in this order

1. Check the battery connector and reconnect it.
2. Replace the battery (CJ2 Hardware User's Manual section 7-2 Replacing the Battery) and replace it periodically from then on.
3. If battery-free operation is used, change the PLC Setup so battery errors are not detected.
4. Battery Error Flag A402.04 can be used in the program to block outputs that rely on retained data.

80CA: I/O bus error

What it means: Data transfer between the CPU Unit and a CP-series Expansion Unit or Expansion I/O Unit failed.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Loose, damaged or wrongly fitted expansion connecting cable
• Damaged Expansion Unit or connector
• Electrical noise on the expansion bus

First checks, in this order

1. Cycle the power.
2. If the error returns, turn the power off and check the connecting cables between the Units and the Units themselves for damage.
3. I/O Bus Error Flag A401.14 is ON and A404 holds 0A0A hex.
4. On a CP1H the display shows 80, CA, 0A, 0A.

80C0 to 80C7: I/O Bus Error

What it means: An error occurred on the bus line between the CPU Unit and the I/O Units on the CPU Rack or an Expansion Rack.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit, I/O Bus Error Flag A401.14 ON

Likely causes

• I/O Connecting Cable disconnected or poorly seated
• Faulty CPU Unit, Unit or I/O Connecting Cable (damaged bus interface)
• Conductive object or foreign matter in a connector
• Electrical noise corrupting bus signals

First checks, in this order

1. Read A404: bits 08 to 15 give the rack number (00 to 03) and bits 00 to 07 the slot number (00 to 09); 0F means it cannot be determined, 0B in the slot byte means the built-in EtherNet/IP port.
2. Turn the power off and on again.
3. If it returns, check the I/O Connecting Cables between all Racks and the seating of every Unit, then restart.
4. Still there: replace the Unit or the I/O Connecting Cable; check FG and power line noise paths.

809F: Cycle time too long error

What it means: The cycle time went over the maximum (watch) cycle time set in the PLC Setup, so the CPU stopped. The CP1E manual calls it Cycle time exceeded error.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Program too long for the maximum cycle time setting
• Long interrupt task processing
• Special I/O Units refreshed every cycle when they do not need it (CP1L, CP1H)
• On CP1E: high-speed counter Z-signal or direction changes at high frequency

First checks, in this order

1. Check the Maximum Interrupt Task Processing Time in A440.
2. Shorten the cycle: move unused code into separate tasks, use jumps (JMP) over sections that are not executed, and disable cyclic refreshing for Special I/O Units that do not need it.
3. Or raise the maximum cycle time in the PLC Setup.
4. On a CP1E using high-speed counters, check the counter input signals.
5. Cycle Time Too Long Flag A401.08 is ON; a CP1H shows 80 9F.

809F: Cycle Time Exceeded Error

What it means: The PLC cycle time exceeded the Watch Cycle Time set in the PLC Setup and the CPU stopped.^[4][6]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• An interrupt task with a long processing time was executed
• A very large repeat count set for FOR(512)
• Program too long for the Watch Cycle Time setting

First checks, in this order

1. Check the Maximum Interrupt Task Processing Time in A440 (not stored when the high-speed interrupt function is enabled in the PLC Setup).
2. Split long interrupt tasks into sections and set a trap in the ladder to watch FOR(512) repeat counts.
3. Reduce the cycle by dividing unused parts into tasks, jumping unused instructions and disabling cyclic refreshing for Special I/O Units that do not need it, or change the Watch Cycle Time.
4. Cycle Time Exceeded Flag A401.08 is ON.

80E1: Too many I/O points error

What it means: More CP-series Expansion Units or Expansion I/O Units (or more allocated words) are connected than the CPU allows.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Too many Expansion Units or Expansion I/O Units on the CPU
• Too many input or output words used by expansion units (CP1H)
• Too many CJ-series Units on the CJ Unit Adapter (CP1H)

First checks, in this order

1. Turn the power off and reconfigure within the limits.
2. CP1E: at most three Expansion Units or Expansion I/O Units on N30/40/60(S) or NA20 CPUs (A407 shows 4000 hex).
3. CP1L: at most three on M30, M40 and M60 CPUs, at most one on L14 and L20 CPUs.
4. CP1H: at most seven CP-series units and 15 input plus 15 output words, at most two CJ-series Units; the display shows 80 E1 then 40 00 (too many words), 60 00 (too many units) or E0 00 (too many CJ-series Units).
5. Too Many I/O Points Flag A401.11 is ON; details are in A407.

80E1: Too Many I/O Points Error

What it means: A configuration limit was exceeded: total I/O points, interrupt inputs, Pulse I/O Modules, Expansion Racks or Units per Rack.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Total I/O points in the I/O tables above the CPU maximum (A407.13 to A407.15 = 000)
• More than 32 interrupt inputs (001)
• Three or more Pulse I/O Modules on a CJ2M CPU Unit (100)
• Too many Expansion Racks (101)
• More than 10 I/O Units on one Rack (111)

First checks, in this order

1. Read A407.13 to A407.15 (the same value is also stored in A407.00 to A407.12) to see which limit was exceeded.
2. Correct the configuration or I/O tables, then turn the power off and back on.
3. Too Many I/O Points Flag A401.11 is ON.

80E0: I/O Setting Error

What it means: The Units actually mounted do not match the registered I/O tables, or the number of Units differs from the table.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• A Unit added, removed or moved after the I/O tables were registered
• A Unit has failed and is not recognized
• Interrupt Input Unit in the wrong slot (A405.08 ON)
• I/O tables from a different CJ2 model downloaded (for example CJ2M-CPU3 tables into a CJ2M-CPU1)
• Loose connector or noise

First checks, in this order

1. Run I/O table verification in CX-Programmer (I/O Table window, Options, Compare with Project) to find the mismatched Unit.
2. If the Unit count is wrong, power off and connect the correct Units; if the count is right, check the Unit in discrepancy and its connector.
3. If the I/O tables are wrong, generate new I/O tables or edit them.
4. Interrupt Input Units must sit in CPU Rack slots 0 to 3 (CJ2H-CPU6-EIP) or 0 to 4 (CJ2H-CPU6, CJ2M-CPU3).
5. I/O Setting Error Flag A401.10 is ON.

80F0: Program error

What it means: A problem in the user program stopped the CPU; a bit in A295 shows which kind.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Instruction processing error, indirect DM BCD error or illegal area access with the PLC Setup set to stop on instruction errors
• END(001) missing at the end of a task
• Task error (executable cyclic task missing, or an interrupt without its matching task)
• Differentiation overflow after many online edits
• Illegal instruction or UM overflow in the transferred program

First checks, in this order

1. Read A295 for the error type, A294 for the task number and A298/A299 for the program address where it stopped.
2. A295.08 instruction processing, A295.09 indirect DM BCD, A295.10 illegal area access, A295.11 No END, A295.12 task error, A295.13 differentiation overflow, A295.14 illegal instruction, A295.15 UM overflow.
3. For illegal instruction or UM overflow, transfer the program again with CX-Programmer.
4. Correct the program, transfer it, then clear the error.
5. On a CP1H the display shows 80 F0 then 01 00, 02 00, 04 00, 08 00, 10 00, 20 00, 40 00 or 80 00 for the eight types in the order above.
6. Program Error Flag A401.09 is ON.

80F0: Program Error

What it means: The user program is incorrect; the address where it stopped is written to A298 and A299 and the error type to A295.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• END(001) missing in a task
• UM overflow, differentiation overflow or illegal instruction
• Task error
• Illegal access, indirect DM/EM BCD error or instruction error with the PLC Setup set to stop on instruction errors

First checks, in this order

1. Check A298/A299 and the A295 flags to find the mistake, correct the program, then clear the error.
2. A295.15 UM overflow or A295.14 illegal instruction: transfer the program again.
3. A295.13 differentiation overflow: return to PROGRAM mode and transfer the program again.
4. Program Error Flag A401.09 is ON.

009B: PLC Setup error

What it means: A setting in the PLC Setup has an invalid value; the program keeps running.^[1][2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Invalid value entered or transferred in the PLC Setup

First checks, in this order

1. Correct the PLC Setup in CX-Programmer and transfer it again.
2. CP1L and CP1H store the internal address of the bad setting in A406 (16-bit binary); the CP1H display shows 00 9B then that address, for example 00 00 to 01 FF.
3. PLC Setup Error Flag A402.10 is ON.

009B: PLC Setup Error

What it means: There is a setting error in the PLC Setup.^[4][6]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Invalid value in a PLC Setup parameter

First checks, in this order

1. Change the indicated setting to a valid value and transfer the PLC Setup again.
2. PLC Setup Error Flag A402.10 is ON.

ERH: ERH indicator lit on a Special I/O Unit (error in the CPU Unit)

What it means: ERH is a red LED on CJ-series Special I/O Units, not a CPU error code. ERH and RUN lit means the Unit is not being refreshed by the CPU (CPU Unit monitoring error) or a bus or CPU WDT error disturbed refreshing. ERH lit with RUN off means the Unit's unit number setting is wrong.^[4][7][3]

Also on: CP1H with CJ-series Special I/O Units on the CJ Unit Adapter (same ERH and RUN entry in the CP1H manual)

PLC response: CPU keeps running; the Special I/O Unit may stop converting or hold its last values

Likely causes

• Cyclic refreshing for the Unit disabled in the PLC Setup and the program does not refresh it with IORF or FIORF often enough
• I/O bus error or CPU Unit WDT error
• Duplicate unit number, or a unit number outside 00 to 95 (RUN off)
• Registered I/O table does not match the Units mounted (RUN off)

First checks, in this order

1. Enable cyclic refreshing for that unit number in the PLC Setup (set its bit to 0), or refresh the Unit from the program with IORF or FIORF at least once every 11 s.
2. Check the CPU Unit for a current error in CX-Programmer; the CPU may log nothing for a monitoring error because it keeps running.
3. With RUN off: check the unit number switch for duplicates and the registered I/O table, then cycle power or toggle the Special I/O Unit Restart Bit.
4. For other ERH conditions see that Unit's operation manual.

ERC: ERC indicator lit on a Special I/O Unit (error detected by Unit)

What it means: ERC is a red LED on CJ-series Special I/O Units, not a CPU error code. On Omron analog input units, ERC and RUN lit means an alarm such as an input disconnection; ERC lit with RUN off means the Unit's initial settings are wrong and it has stopped exchanging data with the CPU.^[7]

Also on: CP1H with CJ-series Special I/O Units on the CJ Unit Adapter

PLC response: CPU keeps running; the Unit raises an alarm or stops conversion

Likely causes

• Broken input wire on a 1 to 5 V or 4 to 20 mA input (disconnection detection)
• Wrong initial settings in the Unit's DM words, for example the mean value processing or conversion time/operation mode setting
• Errors during offset/gain adjustment mode (ADJ LED flashing)

First checks, in this order

1. Read the Unit's alarm flags in its CIO words (n = CIO 2000 + unit number x 10; on many analog input units the flags are in word n+9).
2. Restore any disconnected inputs; the disconnection alarm clears by itself when the input returns.
3. With RUN off, correct the DM settings, then restart the Unit by cycling power or toggling its Special I/O Unit Restart Bit.
4. ERC rules differ by Unit type: check the operation manual of the Unit that shows ERC.

0300 to 035F, 03FF: Special I/O Unit Error

What it means: An error occurred in data exchange between the CPU Unit and a Special I/O Unit; the last two digits are the unit number (03FF means it could not be identified).^[4][6]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Error inside the Special I/O Unit itself
• Faulty connector at the Unit
• Unit failure
• Noise corrupting bus signals

First checks, in this order

1. Check A418 to A423 to find the Unit; the bit for its unit number is ON.
2. Find and fix the cause using that Unit's operation manual.
3. Restart the Unit by toggling its Restart Bit or by cycling power; replace the Unit if it will not restart.
4. Special I/O Unit Error Flag A402.06 is ON.

0200 to 020F: CPU Bus Unit Error

What it means: An error occurred in data exchange between the CPU Unit and a CPU Bus Unit (for example a communications Unit); the last digit is the unit number 0 to F.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Error specific to the CPU Bus Unit
• Faulty connector at the Unit
• Unit failure
• Noise corrupting bus signals

First checks, in this order

1. Check A417: the bit for the failing unit number (00 to 15 = unit 0 to F) is ON.
2. Use I/O table verification to locate the Unit, then check its connector and screws.
3. Fix the cause using the Unit's operation manual, then toggle its Restart Bit or cycle power; replace the Unit if it will not restart.
4. CPU Bus Unit Error Flag A402.07 is ON.

80E9: Unit Number Duplication Error

What it means: The same unit number is set on more than one CPU Bus Unit or more than one Special I/O Unit.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Two CPU Bus Units with the same unit number
• Two Special I/O Units with the same unit number, or words overlapping (a Unit that uses two unit numbers)

First checks, in this order

1. Check A410 (CPU Bus Unit duplicated number flags, bits 00 to 15 = units 0 to F) and A411 to A416 (Special I/O Unit duplicated number flags, units 0 to 95).
2. Change the unit number switches so each is used once.
3. Turn the Rack power off and back on.
4. Duplication Error Flag A401.13 is ON.

WDT: CPU error (WDT error)

What it means: The watchdog timer inside the CPU Unit timed out, so the CPU itself stopped working; A400 is not updated with an error code.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit, outputs off

Likely causes

• CPU Unit hardware fault
• Severe electrical noise

First checks, in this order

1. Tell it apart from a fatal error: the LEDs look the same (RUN off, ERR/ALM lit) but CX-Programmer cannot go online during a CPU error.
2. On a CP1H the 7-segment display is blank or frozen.
3. Cycle the power. If it happens again, the Unit may be faulty: consult Omron or replace the CPU Unit.

WDT: CPU Error (WDT error)

What it means: A CPU error occurs in the CPU Unit itself when the watchdog timer times out; Programming Devices cannot connect and A400 is not updated with an error code.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• CPU Unit failure
• A conductive object inside the Unit
• Noise making the CPU microcomputer malfunction

First checks, in this order

1. Cycle the power and see whether the error clears or returns.
2. Look for conductive objects (for example metal chips) and clean the Unit with an air blower; keep metal work away from the open control panel.
3. Check noise paths (FG, power lines).
4. If it returns or happens often, replace the CPU Unit.

C101 to C2FF: FALS error (FALS instruction executed)

What it means: A FALS instruction in the user program created a user-defined fatal error; the code is C100 hex plus the FALS number (001 to 1FF hex, FALS 1 to 511).^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• A machine condition the programmer chose to treat as fatal (the FALS execution condition in the ladder)

First checks, in this order

1. Subtract C100 hex from the code to get the FALS number, then find that FALS instruction in the program and see what triggers it.
2. Remove the cause, then clear the error from CX-Programmer.
3. Unlike other fatal errors, I/O memory is not cleared for a FALS error.
4. FALS Error Flag A401.06 is ON; a CP1H shows C1 01 for FALS 001.

C101 to C2FF: FALS(007) Error

What it means: FALS(007) was executed in the program; the leftmost digit is C and the right three digits (101 to 2FF hex) match FAL numbers 001 to 511.^[4][5][6]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• User-defined fatal condition programmed with FALS(007)

First checks, in this order

1. Find the FALS number from the code and correct the condition it reports.
2. Then perform the error read/clear operation from CX-Programmer.
3. FALS Error Flag A401.06 is ON.

4101 to 42FF: FAL instruction executed

What it means: A FAL instruction in the user program created a user-defined non-fatal error; FAL numbers 001 to 511 become codes 4101 to 42FF.^[1][2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• A machine condition the programmer flagged as an alarm with FAL

First checks, in this order

1. Read A360 to A391 (Executed FAL Number Flags) or the code to get the FAL number, then check its execution condition in the program.
2. Remove the cause. Clear the error by executing FAL with FAL number 00 or from CX-Programmer.
3. FAL Error Flag A402.15 is ON; a CP1H shows 41 01 for FAL 001.

4101 to 42FF: FAL(006) Error

What it means: FAL(006) was executed in the program; the leftmost digit is 4 and the right three digits (101 to 2FF hex) match FAL numbers 001 to 511.^[4][5][6]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• User-defined non-fatal condition programmed with FAL(006)

First checks, in this order

1. Check A360 to A391 for the executed FAL number and correct the condition.
2. Clear it by executing FAL(006) with FAL number 00 or with the error read/clear operation in CX-Programmer.
3. FAL Error Flag A402.15 is ON.

80F0: Program error: No END error

What it means: A task in the program is missing its END(001) instruction (A295.11 ON).^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• END(001) deleted or never added at the end of a task's program

First checks, in this order

1. Read A294 for the task number.
2. Insert END(001) at the end of that task's program and transfer it again.
3. On a CP1H the display shows 80 F0 08 00.

80F0: Program Error: No END error

What it means: A295.11 is ON: the task given in A294 does not end with END(001).^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• END(001) missing at the end of a task

First checks, in this order

1. Read A294 (program stop task number).
2. Add END(001) at the end of that task and transfer the program again.

80F0: Program error: Task error

What it means: A295.12 is ON: either every cyclic task is set not to run, or an interrupt fired (input, high-speed counter, scheduled or external interrupt) whose interrupt task was never created.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Every cyclic task is set not to start when operation starts
• Interrupt enabled but its interrupt task was never created

First checks, in this order

1. Check the cyclic task properties and set at least one task to start when operation starts.
2. Create a task for the number stored in A294.
3. On a CP1H the display shows 80 F0 10 00.

80F0: Program Error: Task error

What it means: A295.12 is ON: an executable cyclic task is missing, or an interrupt came in whose task does not exist (the second case only when Stop CPU on Instruction Error is set in the PLC Setup).^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Startup cyclic task attributes not set
• TKON(820), TKOF(821) or MSKS(690) points to a task that does not exist
• Power OFF interrupt task enabled in the PLC Setup but not created

First checks, in this order

1. Check the startup cyclic task attributes and the task control by TKON(820) and TKOF(821).
2. Make sure every task number used by TKON, TKOF and MSKS exists; mask unused I/O or scheduled interrupts with MSKS(690).
3. If the power OFF interrupt task is enabled, create it.

80F0: Program error: Instruction processing error

What it means: A295.08 is ON: an instruction could not run because of bad operand data, and the PLC Setup is set to stop the CPU on instruction errors.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Operand data out of range for the instruction (ER Flag turned ON)
• PLC Setup set to stop operation on instruction errors

First checks, in this order

1. Read A298 and A299 for the program address that failed, check that instruction's operand rules and fix the data.
2. Or set the PLC Setup so instruction errors do not stop the CPU.
3. On a CP1H the display shows 80 F0 01 00.

80F0: Program Error: Instruction error

What it means: Instruction Error Flag A295.08 is ON: incorrect operand data made the ER Flag turn ON, and the PLC Setup is set to stop on instruction errors.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Invalid operand values at run time

First checks, in this order

1. Use the Program Error Position in A298/A299 to find the instruction and correct its operand data per the Instructions Reference Manual (W474).

80F0: Program error: Illegal area access error

What it means: A295.10 is ON: an instruction tried to read or write an area it may not access, and the PLC Setup is set to stop on instruction errors.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Reading or writing the parameter area
• Writing to an area without memory installed
• Writing to a write-protected area
• Indirect DM addressing BCD error

First checks, in this order

1. Read A298 and A299 for the failing program address and change the addressing so the illegal access cannot happen.
2. Check indirect and offset addressing so the final address stays inside the intended area.
3. On a CP1H the display shows 80 F0 04 00.

80F0: Program Error: Illegal access error

What it means: A295.10 is ON: an illegal access occurred and the PLC Setup is set to stop operation for an instruction error.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Reading or writing a parameter area
• Writing memory that is not installed
• Writing an EM bank used as EM file memory
• Writing to a read-only area
• Indirect DM/EM address not in BCD while BCD mode is selected

First checks, in this order

1. Find the address in A298/A299 and correct the instruction or its addressing.

80F0: Program error: Differentiation overflow error

What it means: A295.13 is ON: differentiated instructions were inserted or deleted so many times during online editing that a system limit was exceeded.^[1][2][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Many online edits adding or removing differentiated (up/down) instructions

First checks, in this order

1. Switch the CPU to PROGRAM mode and then back to MONITOR mode (confirm the machine is safe first).
2. On a CP1H the display shows 80 F0 20 00.

008B: Interrupt task error

What it means: Detect Interrupt task errors is on in the PLC Setup and an interrupt task refreshed a Special I/O Unit with IORF(097) while cyclic refreshing of that Unit was also active (duplicate refreshing).^[2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• IORF(097) in an interrupt task on a Special I/O Unit that is also refreshed cyclically

First checks, in this order

1. Read A426 for the Special I/O Unit involved.
2. Change the program so the Unit is refreshed only one way, or disable interrupt task error detection in the PLC Setup if that is acceptable.
3. Interrupt Task Error Flag A402.13 is ON; a CP1H shows 00 8B then 80 0x with the unit number.

008B: Duplicated Refreshing Error (CJ1: Interrupt task error)

What it means: Detect Duplicated Refresh Errors is enabled in the PLC Setup and IORF(097), FIORF(225), IORD(222) or IOWR(223) in an interrupt task conflicts with the same Unit being refreshed by a cyclic task or by normal I/O refresh.^[4][6]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• The same Special I/O Unit refreshed from both a cyclic task and an interrupt task
• IORF(097), FIORF(225), IORD(222) or IOWR(223) executed in an interrupt task during I/O refreshing while cyclic refreshing of that Unit is enabled

First checks, in this order

1. Read A426 for the unit number involved.
2. Correct the program so only one refresh path is used, or disable duplicated refresh detection in the PLC Setup.
3. Flag A402.13 is ON (Duplicated Refresh Error Flag on CJ2, Interrupt Task Error Flag on CJ1).

009A: Basic I/O Error

What it means: An error occurred in a CJ-series Basic I/O Unit, for example a blown fuse or missing external supply.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Blown fuse in an Output Unit
• External 24 V power supply to the Unit off or disconnected
• Other errors specific to the Unit

First checks, in this order

1. Read A408 for the rack and slot of the Unit.
2. Measure the voltage at the Unit's power supply terminals and confirm 24 V is present.
3. Replace the fuse if blown and check the maximum switching current of the loads.
4. Basic I/O Unit Error Flag A402.12 is ON.

00F1: Backup memory error (CP1E), Flash memory error (CP1L, CP1H)

What it means: Writing to the CPU's built-in backup memory (EEPROM on CP1E, flash memory on CP1L and CP1H) failed.^[1][2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Built-in backup or flash memory worn out after more than 100,000 writes
• CPU Unit memory hardware fault

First checks, in this order

1. Check A315.15 (Backup Memory Error Flag on CP1E, Flash Memory Error Flag on CP1L and CP1H); A402.00 Other Non-fatal Error Flag is also ON on CP1L and CP1H.
2. Replace the CPU Unit if the memory has been written more than 100,000 times.
3. A CP1H shows 00 F1.

00F1: Backup Memory Error

What it means: Writing to the built-in flash memory failed; operation may not be possible the next time power is restored.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Built-in flash memory write failure in the CPU Unit

First checks, in this order

1. Plan a CPU Unit replacement before the next power cycle if possible.
2. Backup Memory Error Flag A315.15 is ON.

80CE: I/O Bus Error

What it means: I/O bus error reported when the End Cover is not connected to the CPU Rack or an Expansion Rack (A404 shows 0E hex).^[4][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• End Cover missing or not fully latched on the right end of a Rack

First checks, in this order

1. Check that an End Cover is fitted and locked at the end of the CPU Rack and every Expansion Rack.
2. Turn the power off and on again after fitting it.
3. I/O Bus Error Flag A401.14 is ON.

80CF: I/O Bus Error

What it means: I/O bus error where the CPU could not determine the rack or slot (A404 shows 0F hex).^[4][3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• I/O Connecting Cable fault
• Faulty Unit or connector
• Noise on the bus

First checks, in this order

1. Turn the power off and on again.
2. Check all I/O Connecting Cables and Unit connections; replace the suspect Unit or cable if the error returns.
3. I/O Bus Error Flag A401.14 is ON.

80EA: Rack Number Duplication Error (Expansion Rack Duplicated Rack Number)

What it means: The same I/O word is allocated to more than one Basic I/O Unit, or an Expansion Rack's starting word is beyond CIO 0901.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Overlapping word allocation between Units on different Racks
• Expansion Rack first word set above the valid range

First checks, in this order

1. Check A409.00 to A409.03 to see which Rack (0 to 3) is affected.
2. Correct the allocations so no word is used twice, or set the Rack's first word below CIO 0900 with CX-Programmer.
3. Turn the Rack power off and back on.
4. Duplication Error Flag A401.13 is ON.

0400 to 040F: CPU Bus Unit Setting Error

What it means: An installed CPU Bus Unit does not match the CPU Bus Unit registered in the I/O tables; the last digit is the unit number.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• CPU Bus Unit replaced with a different model or moved
• Registered I/O table out of date

First checks, in this order

1. Check A427 for the unit number flag that is ON.
2. Fit the correct Unit, or change the registered I/O table to match.
3. CPU Bus Unit Setting Error Flag A402.03 is ON.

0500 to 055F: Special I/O Unit Setting Error

What it means: An installed Special I/O Unit does not match the registered I/O tables, or a Unit set for synchronous unit operation is missing, unsupported or not on the CPU Rack.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Special I/O Unit model differs from the registered I/O table
• Unit specified for synchronous unit operation does not support it or does not exist
• Synchronous Unit mounted on an Expansion Rack instead of the CPU Rack

First checks, in this order

1. Check A428 to A433 to find the Unit.
2. Change the registered I/O table, or correct the synchronous unit operation settings in the PLC Setup and transfer it again.
3. Move the Synchronous Unit to the CPU Rack and fix the registered I/O table if needed.
4. Special I/O Unit Setting Error Flag A402.02 is ON.

00D1: Option Board error (option slot 1)

What it means: The Option Board in slot 1 was removed while the power was on.^[1][2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Option Board pulled or loosened with power applied

First checks, in this order

1. Turn the power off, refit the Option Board, then power up.
2. Option Board Error Flag A315.13 and Other Non-fatal Error Flag A402.00 are ON; A424 shows the board (CP1E, CP1H).
3. A CP1H shows 00 d1.

00D2: Option Board error (option slot 2)

What it means: The Option Board in slot 2 was removed while the power was on.^[2][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Option Board pulled or loosened with power applied

First checks, in this order

1. Turn the power off, refit the Option Board, then power up.
2. A315.13 and A402.00 are ON.
3. A CP1H shows 00 d2.

00D1: Option Board Error

What it means: The Option Board was removed while the system was operating, or the Option Board has failed (CJ2M CPU Units that take Option Boards).^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Option Board removed during operation
• Option Board failure
• Vibration or shock loosening the board

First checks, in this order

1. Check the mating of the Option Board connector and reconnect it.
2. If restarting does not clear it, replace the Option Board.
3. A315.13 Option Board Error Flag and A402.00 Other Non-fatal Error Flag are ON.

008A: Built-in analog error (CP1E NA-type), Built-in analog I/O error (CP1H XA)

What it means: The CPU Unit's built-in analog inputs or outputs have an error and built-in analog I/O stops.^[1][3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Fault in the built-in analog I/O circuit of the CPU Unit

First checks, in this order

1. Cycle the power. If the error stays, replace the CPU Unit.
2. Built-in Analog Error Flag A315.14 and A402.00 are ON; on CP1E the details are in A434.
3. A CP1H shows 00 8A.

0200 to 020F: CPU Bus Unit error

What it means: A data exchange error occurred between the CP1H CPU Unit and a CJ-series CPU Bus Unit on the CJ Unit Adapter; the last digit is the unit number 0 to F.^[3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Error in the CPU Bus Unit
• Connection fault between the CPU Unit, CJ Unit Adapter and Unit

First checks, in this order

1. Check A417 for the unit number.
2. Fix the cause using the Unit's manual, then turn ON its Restart Bit or cycle power; replace the Unit if it does not recover.
3. CPU Bus Unit Error Flag A402.07 is ON; the display shows 02 00 to 02 0F.

0300 to 035F, 03FF: Special I/O Unit error

What it means: A data exchange error occurred between the CP1H CPU Unit and a CJ-series Special I/O Unit; 03FF means the unit number is unknown.^[3]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Error in the Special I/O Unit
• Connection fault on the CJ Unit Adapter side

First checks, in this order

1. Check A418 to A423 for the unit number.
2. Fix the cause using the Unit's manual, then turn ON its Restart Bit or cycle power; replace the Unit if it does not recover.
3. Special I/O Unit Error Flag A402.06 is ON; the display shows 03 00 to 03 5F, or 03 FF.

80C0 to 80C7: I/O bus error for CJ-series Units

What it means: Data transfer failed with a CJ-series Unit connected through the CJ Unit Adapter; the location word shows first (00 00) or second (00 01) CJ-series Unit.^[3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Damaged CJ-series Unit
• Bad connection between the CPU Unit, CJ Unit Adapter and CJ-series Units

First checks, in this order

1. Read the display (80 C0 then 00 00 or 00 01) or A404 to find the Unit.
2. Check the Unit for damage and replace it if required.
3. I/O Bus Error Flag A401.14 is ON.

80CE: I/O bus error for CJ-series Units, no End Cover

What it means: CJ-series Units are connected to the CP1H through the CJ Unit Adapter but the End Cover is not installed.^[3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• End Cover missing or not latched after the last CJ-series Unit

First checks, in this order

1. Install the End Cover properly, then cycle power.
2. The display shows 80 CE 0E 0E; A401.14 is ON.

80CF: I/O bus error for CJ-series Units, error location unknown

What it means: A data transfer error occurred with the CJ-series Units, but the CPU could not tell where.^[3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Connection problem between the CPU Unit, CJ Unit Adapter and CJ-series Units

First checks, in this order

1. Check the connections between the CPU Unit, the CJ Unit Adapter and each CJ-series Unit, then cycle power.
2. The display shows 80 CF 0F 0F; A401.14 is ON.

80E0: I/O setting error

What it means: A Unit that cannot be used with the CP1H is connected: a CJ-series Basic I/O Unit or an I/O Control Unit.^[3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• CJ-series Basic I/O Unit or I/O Control Unit mounted on the CJ Unit Adapter

First checks, in this order

1. Turn the power off and remove the unsupported Unit.
2. The display shows 80 E0; I/O Setting Error Flag A401.10 is ON.

80E9: Duplicate number error

What it means: The same unit number is set on more than one CJ-series CPU Bus Unit or Special I/O Unit connected to the CP1H.^[3]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Two CJ-series Units with the same unit number switch setting

First checks, in this order

1. Turn the power off and set unique unit numbers.
2. The display shows 80 E9 then 00 01 for CPU Bus Unit No. 1 or 80 01 for Special I/O Unit No. 1.
3. Duplication Error Flag A401.13 is ON; see A410 (CPU Bus Units) and A411 to A416 (Special I/O Units).

er: er on the 7-segment display (Memory Cassette transfer failed)

What it means: On a CP1H, er flashes for 5 s when a data transfer or verification between the Memory Cassette and the CPU Unit fails; a successful transfer ends with 00 flashing instead.^[3]

PLC response: Shown during Memory Cassette transfer; display clears after 5 s

Likely causes

• Transfer or verification error between the Memory Cassette and the CPU Unit
• Power turned off or cassette removed during the transfer

First checks, in this order

1. Repeat the transfer in PROGRAM mode (Memory Cassette transfers do not run in RUN or MONITOR mode).
2. While BKUP and the display are flashing, do not turn off power or remove the Memory Cassette; doing so can make the cassette unusable.
3. If the cassette is used for automatic transfer at startup and the needed data is missing, the CPU raises memory error 80F1 instead.

80F4: Memory Card Transfer Error

What it means: At power-up the CPU could not correctly read the Memory Card for automatic transfer, or the card's program includes network symbols the CPU cannot accept.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Files needed for automatic transfer at startup missing from the Memory Card
• User program (OBJ file) with network symbols on CJ2H-CPU6 unit version 1.5 or earlier, or CJ2M-CPU1 unit version 2.1 or earlier

First checks, in this order

1. Check that the Memory Card holds every file needed for automatic transfer.
2. Use a user program (OBJ file) without network symbols on the older unit versions.
3. Memory Card Error Flag A401.03 is ON.

80F2: Version Error

What it means: The transferred user program uses functions that the CPU Unit's unit version does not support.^[4]

PLC response: CPU stops, RUN off, ERR/ALM lit

Likely causes

• Program written for a newer CPU unit version than the one installed

First checks, in this order

1. Check the CPU unit version against the functions the program uses.
2. Replace the CPU Unit with one of a supported unit version, or rework the program.
3. Version Error Flag A401.05 is ON.

00F2: Tag Memory Error

What it means: An error occurred in the memory where network tags (network symbols) are stored.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Tag memory data error in the CPU Unit

First checks, in this order

1. Transfer the program again.
2. Tag Memory Error Flag A315.12 is ON.
3. Applies only to CJ2H-CPU6-EIP, CJ2M-CPU3, CJ2H-CPU6 unit version 1.6 or later and CJ2M-CPU1 unit version 2.2 or later.

00F3: System Work Error

What it means: An error occurred in the memory used for online editing; operation may not be possible after the next power interruption.^[4]

PLC response: Operation continues, RUN lit, ERR/ALM flashing

Likely causes

• Online editing memory error in the CPU Unit

First checks, in this order

1. Transfer the program again before the next power cycle.
2. System Work Error Flag A315.04 and Other Non-fatal Error Flag A402.00 are ON.