Mitsubishi QCPU
The MELSEC-Q series QCPU provides high-performance processing, stable system control, and flexible system configuration for medium to large-scale industrial automation.
It is designed for applications requiring high reliability, large program capacity, and multi-CPU system support, such as packaging lines, printing systems, converting equipment, and complex production machinery.
Key Features
- High-performance CPU architecture for fast instruction execution
- Support for multiple CPU systems and distributed control
- Large memory capacity for complex programs and data processing
- Advanced diagnostics and system protection functions
- Flexible communication and control with intelligent modules and networks
The QCPU series enables stable system operation, reliable multi-CPU coordination, and efficient troubleshooting in demanding industrial environments.
Find the Error Code List and Troubleshooting
1️⃣ Version & Compatibility Errors
| Error Code | Error Name | Cause | Solution |
| 2000 | UNIT VERIFY ERROR | QCPU function version A is used in a multiple CPU system. Multiple CPU systems require function version B or later. | Replace all CPUs with function version B or later, then power cycle the system. |
| 2125 | SP.UNIT LAY ERROR | Multiple CPU configuration detected while using unsupported CPU function versions. | Upgrade CPU modules to a compatible function version and recheck system configuration. |
| 7010 | MULTI EXE. ERROR | Mixed CPU function versions (version A and version B) are installed in the same multiple CPU system. | Standardize all CPUs to the same function version (version B or later) and restart the system. |
2️⃣ Module Layout & Hardware Limit Errors
| Error Code | Error Name | Cause | Solution |
| 2124 | SP.UNIT LAY ERR | The number of mounted I/O modules exceeds the maximum allowed for the base unit in a multiple CPU system. | Reduce the number of I/O modules to comply with the base unit specification, or add an extension base. |
| 2150 | SP.UNIT VER.ERR | A CPU other than CPU No.1 is assigned as the control CPU for a communication module (e.g. serial or network module). | Set CPU No.1 as the control CPU in PLC parameters, then restart the system. |
3️⃣ Parameter & Configuration Errors
| Error Code | Error Name | Cause | Solution |
| 3009 | PARAMETER ERROR | Different control CPUs are assigned to AnS/A series modules on the same base unit in a multiple CPU configuration. | Set the same control CPU for all AnS/A series modules on the base, then write parameters and restart the system. |
| 3012 | PARAMETER ERROR | Multiple CPU parameters are inconsistent between CPUs (consistency check failure at startup). | Align the multiple CPU settings across all CPUs (system configuration, PLC count, assignments), then reset CPU No.1. |
| 3015 | PARAMETER ERROR | Parameter inconsistency or unsupported parameter combination within the multiple CPU system (startup parameter validation failure). | Correct the related parameters to a supported combination, write parameters to all CPUs, then reset CPU No.1. |
4️⃣ Access & Shared Memory Errors
| Error Code | Error Name | Cause | Solution |
| 2110 | SP.UNIT ERROR | An instruction attempted to access a CPU module that is not physically mounted in the multiple CPU system. | Verify CPU mounting position and slot configuration, then correct the access instruction. |
| 2114 | SP.UNIT ERROR | Invalid read or write access to the local CPU shared memory using a restricted instruction in a High-Performance or Process CPU. | Use permitted instructions (such as S.TO) or change CPU type to Universal model if required. |
| 2115 | SP.UNIT ERROR | Writing to the shared memory area of another CPU using an unsupported instruction. | Do not write directly to other CPUs’ shared memory. Use auto-refresh or approved inter-CPU data exchange methods. |
| 2116 | SP.UNIT ERROR | Writing to the buffer memory of an intelligent function module that is controlled by another CPU. | Reassign the control CPU for the module or restrict access to read-only operations. |
| 4102 | OPERATION ERROR | Link direct device was used to access a module that is not controlled by the local CPU. | Access only modules controlled by the local CPU and revise device addressing accordingly. |
5️⃣ Execution & Instruction Load Errors
| Error Code | Error Name | Cause | Solution |
| 4107 | OPERATION ERROR | The number of unprocessed multiple-CPU or motion-related instructions exceeds the allowable limit (33 or more queued). | Limit the number of simultaneously executed instructions to 32 or fewer. Add interlocks or sequence control to stagger instruction execution. |
6️⃣ System STOP / Multi-CPU Control Errors
| Error Code | Error Name | Cause | Solution |
| 7000 | MULTI CPU DOWN | A reset or STOP-level error occurred in a CPU other than CPU No.1, or “All station stop” is enabled during a major error. | Identify and eliminate the original error cause, then reset CPU No.1 or power-cycle the system. |
| 7020 | MULTI EXE. ERROR | A STOP error occurred in one CPU while “All station stop” is disabled, allowing the system to continue operating. | Locate and correct the error in the affected CPU to prevent further system instability. |
7️⃣ Error Code Summary (Quick Reference)
| Category | Error Codes | Description |
| Version & Compatibility | 2000, 2125, 7010 | Errors caused by incompatible or mixed CPU function versions in a multiple CPU system. |
| Module Layout & Hardware Limits | 2124, 2150 | Errors related to exceeding base unit specifications or incorrect control CPU assignment. |
| Parameter & Configuration | 3009, 3012, 3015 | Multiple CPU parameter inconsistencies detected during startup or configuration checks. |
| Access & Shared Memory | 2110, 2114, 2115, 2116, 4102 | Illegal access to CPU shared memory, buffer memory, or modules controlled by another CPU. |
| Execution & Instruction Load | 4107 | Excessive unprocessed multiple-CPU or motion instructions queued at the same time. |
| System STOP / Multi-CPU Control | 7000, 7020 | STOP-level errors affecting overall multiple CPU operation and execution control. |
8️⃣ Intelligent / Analog Module Errors (Typical)
| Step | Action | Engineering Purpose |
| 1 | Check CPU status and LED indicators | Confirm whether the system is in RUN or STOP state and identify major fault conditions immediately. |
| 2 | Open GX Works2 / GX Works3 diagnostics | Access detailed error codes, error sources, and module-level diagnostics. |
| 3 | Review Event History | Identify the first error; subsequent errors are often secondary effects. |
| 4 | Verify hardware configuration | Check CPU arrangement, module layout, control CPU assignment, and wiring. |
| 5 | Confirm multiple CPU parameters | Ensure parameter consistency across all CPUs before attempting system restart. |
| 6 | Correct root cause and reset CPU No.1 | Multiple CPU systems require CPU No.1 to be reset after fault correction. |
9️⃣ I/O Troubleshooting
| Item | Included in This List | Not Included in This List |
| Error scope | QCPU multiple CPU system errors documented in the QCPU User’s Manual (Multiple CPU System) | FX, L, iQ-R series errors or single CPU system errors |
| Error type | System STOP errors, configuration errors, parameter errors, access violations | Instruction-level runtime errors (C**** / F**** series) |
| Source | CPU-level and system-level diagnostics | Intelligent module–specific error tables (analog, motion, network) |
| Tool dependency | Errors confirmed via GX Works2 / GX Works3 diagnostics | Compile-time or online-edit tool warnings only |
| Completeness | All error codes explicitly listed in the Multiple CPU System manual | A theoretical “complete Mitsubishi error list” |
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