P0687
ECM/PCM Power Relay Control Circuit High
Onboard computer / power supply
Generic OBD-II
High
What it means
P0687 means the engine computer sees the control circuit for its own main power relay reading high — voltage present when it shouldn't be, or the relay not switching as commanded. Because this relay supplies power to the ECM/PCM and related systems, the fault can cause hard starting, stalling, or the module failing to power down correctly.
High
Can I keep driving? Risky — the main power relay feeds the engine computer, so a no-start or sudden stall is possible; get it fixed before relying on the car.
Common symptoms
What you'll notice
- Check-engine light on
- Hard starting, intermittent no-start, or unexpected stalling
- Battery drain from the module or relay not powering down
- Multiple unrelated codes set when the module loses power
Common causes
Most likely first
- Faulty ECM/PCM power relayLikely
- Short to voltage in the relay control circuitCommon
- Corroded or loose connections at the relay or moduleCommon
- Failed ECM/PCM driverLess often
How to diagnose & fix
Work through it in order
- Scan and note whether the code is current or intermittent.
- Test the power relay and its socket; swap in a known-good identical relay if available.
- Check the relay control wiring for a short to battery voltage and verify grounds.
- If the relay and wiring are good, the module driver may be at fault — confirm before replacing. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0687?+
Not reliably — if the main power relay circuit acts up the car can stall or fail to start. Treat it as something to fix promptly.
Can I just clear P0687?+
It may clear briefly, but a bad relay or control-circuit short will bring it back and can leave you stranded.
Related codes
Often seen with P0687
Read & clear P0687 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX