OBD-II code · Powertrain (generic)
P0688 ECM/PCM Power Relay Sense Circuit High
ECM/PCM Power Relay Sense Circuit High: the signal voltage is above the expected range. Often an open circuit or a short to supply voltage.
Is it safe to drive with P0688?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyMain relay contacts stuck closed
- PossibleSense wire shorted to power
- Less likelyConnector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.3–2 h
- Emissions test
- Likely to fail
- Parts involved
- Ecm, Main Relay
Related codes
- P0686ECM/PCM Power Relay Control Circuit Open
- P0687ECM/PCM Power Relay Sense Circuit Open
- P0685ECM or PCM Power Relay Control Circuit Open
- P0689ECM or PCM Power Relay Sense Circuit Low
- P068AECM or PCM Power Relay De-Energized Performance Too Early
- P068BECM or PCM Power Relay De-Energized Performance Too Late
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.