Powertrain
generic / SAE
P0688
ECM/PCM Power Relay Sense Circuit High
The ECM cannot detect that the main power relay has switched on. The sense input remains low when commanded high.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number6 / 88
Possible causes
- Main relay contacts stuck closed high
- Sense wire shorted to power medium
- Connector pins corroded - high contact resistance low
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
Inspection / repair
- Difficulty: medium
- DIY: shop recommended
- Estimated cost: 80–400 €
- Estimated time: 0.3–2 h
- Component: ecm
- Component: main relay
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012