OBD-II code · Powertrain (generic)
P0686 ECM/PCM Power Relay Control Circuit Open
The control circuit for the ECM main power relay is open. Without this relay, the controller cannot maintain its keep-alive supply.
Is it safe to drive with P0686?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyMain relay defective
- PossibleRelay control wire open
- Less likelyPin pushed back out of connector body
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, Relay Wiring
Related codes
- P0687ECM/PCM Power Relay Sense Circuit Open
- P0688ECM/PCM Power Relay Sense Circuit High
- P0683Glow Plug Control Module 1 to PCM Communication Circuit
- P0684Glow Plug Control Module 1 to PCM Communication Range or Performance
- P0685ECM or PCM Power Relay Control Circuit Open
- P0689ECM or PCM Power Relay Sense Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.