P0686
PowertrainPcm Powerhigh severityECM/PCM Power Relay Control Circuit Low
What P0686 Means
The PCM detects a low voltage condition in the ECM/PCM power relay control circuit. This can lead to intermittent power loss to the control module.
Symptoms
- Intermittent no-start
- Engine stalling
- Erratic module behavior
Common Causes
- Short to ground in control circuit
- Faulty power relay
- Corroded connectors
- PCM fault
Diagnostic Steps
- Measure control circuit voltage
- Inspect wiring for short to ground
- Test power relay resistance
- Check PCM ground and connections
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