P0687ECM/PCM Power Relay Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. P0687 means the control line is shorted to voltage: when the driver switches on and should pull it to ground, it stays high (0.5 Ω or less to positive) or the driver goes into overcurrent protection, so the relay does not pull in – no supply to the loads, no start or stalling. GM checks with run/crank voltage above 11 V and sets the code after 8 of 10 samples at 250 ms, with the lamp after two trips. The former obdex title (a sense-circuit wording) was a shifted entry; P0687 is the 'high' code of the control circuit. A high voltage on the sense line is P0690.
- What you may notice
- Check engine light
- Engine does not start or stalls
- Relay does not click
- Likely causes
- LikelyControl wire shorted to positive (harness, external voltage)
- PossibleRelay coil shorted (very low resistance)
- RareModule driver faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.