Fault Code Diagnosis System for EFI Diesel Generators

The Electronic Control Unit (ECU) of an electronically fuel-injected (EFI) diesel generator is equipped with a self-diagnostic system. When a fault occurs, the ECU activates necessary protective measures for the control system, stores the fault as a code in Random Access Memory (RAM), and illuminates the CHECK engine light simultaneously.

(1) Fault Code Reading Method

Before reading fault codes, the following preparations must be completed:

① Verify that the fault indicator light functions properly.

② Ensure safety precautions are in place for test runs during code reading.

③ Confirm all mechanical connections are secure.

④ Check that the battery voltage is normal.

⑤ Close the throttle after the engine has warmed up to operating temperature.

⑥ Turn off all auxiliary electrical devices.

Fault code meanings and reading methods vary across diesel generator models and production years; therefore, diagnosis should be tailored to specific cases.

(2) Fault Code Clearing Method

After identifying the fault location using the fault code table and resolving the issue, the fault codes stored in the ECU must be cleared. Failure to do so will result in persistent storage of old codes, which may be repeatedly output alongside new fault codes in the future.

Clearing fault codes is relatively simple: turn the ignition switch to the "OFF" position and disconnect the negative battery terminal. However, this method will also erase other memory system data.

(3) Tips to Avoid False Code Interference

While self-diagnostic fault code reading simplifies troubleshooting, improper operation or procedural errors during reading can cause confusion. The following tips ensure accurate self-diagnosis:

① Optimal Engine Temperature: Reading codes when the engine coolant temperature is between 85°C and 95°C is most reliable. Testing without reaching normal operating temperature may generate false fault codes (e.g., for coolant temperature, exhaust gas recirculation, or idle issues), misleading users into assuming multiple electronic control system failures.

② Distinguish Valid vs. Invalid Codes: False codes may arise from:

a. Incomplete clearing of previous fault codes during maintenance.

b. Accidental disconnection of sensor connectors by maintenance personnel while the engine is running.

③ Static vs. Dynamic Code Timing: Static codes are read with the ignition switch on (engine not running), while dynamic codes require the engine to be started. Note the sequence and transition procedures: typically, static codes should be cleared before reading dynamic codes.

(4) Memory Correction Requires a Break-In Period

After reading codes, clearing them, and resolving faults, temporary reduced acceleration performance may occur. This is normal and requires technicians to perform "driving condition memory correction" on the ECU. In short, this process restores the ECU’s ability to adapt to the generator’s current operating conditions.

(5) Fault Codes Are Not the Sole Diagnostic Basis

Fault codes provided by the ECU only relate to internal/external circuits of the indicated component and do not reflect issues with other circuits or mechanical failures of the component itself. Diesel generator faults have multiple potential causes, and fault codes merely indicate a "yes/no" status for specific conditions, not the exact root cause.

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