What this code means

The ECU detected a malfunction in the K40 relay module voltage supply circuit. The K40 module is a central relay and fuse module on Mercedes-Benz vehicles that controls power distribution to multiple engine management systems.

Symptoms

• Check Engine Light
• Multiple system faults
• Engine may not start
• Intermittent electrical failures
• Various warning lights

Common causes

• Faulty K40 relay module
• Corroded K40 module connector
• Power supply wiring damage
• Water intrusion in K40 module
• Internal relay module failure

Diagnostic steps

1. Test K40 module power supply and outputs
2. Inspect K40 module connector for corrosion
3. Check for water intrusion
4. Test individual relay outputs
5. Inspect wiring to K40 module

Repair notes

Replace the K40 relay module; check for water intrusion source.

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