P0687 code meaning
ECM/PCM Power Relay Control Circuit High
Powertrain system Generic code P06xx codes Check engine light
What P0687 means
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.
P0687 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0687
- Check engine light
- Engine does not start or stalls
- Relay does not click
Common causes of P0687
- Most likelyControl wire shorted to positive (harness, external voltage)
- PossibleRelay coil shorted (very low resistance)
- Less likelyModule driver faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
ECM power relayRelay control circuitEngine control module
What each part of P0687 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 87 | The exact fault in that area. |
What to do next
- Note P0687 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0687
What does P0687 mean?
P0687 means "ECM/PCM Power Relay Control Circuit High". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0687?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0687 fail an emissions test?
Yes, it can. P0687 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0687 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0687 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.