P0688
PowertrainPcm Powerhigh severityECM/PCM Power Relay Sense Circuit /Open
What P0688 Means
The PCM detects an open in the sense circuit used to monitor the ECM/PCM power relay output. The module cannot confirm relay power status.
Symptoms
- Intermittent no-start
- Stored power relay codes
- Erratic startup behavior
Common Causes
- Open sense circuit wiring
- Faulty power relay
- Corroded connector pins
- PCM fault
Diagnostic Steps
- Inspect sense circuit for open
- Test relay output voltage
- Check connector and pin integrity
- Verify PCM sense input
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