Symptoms of P0687
- Check-engine light, sometimes with several unrelated codes at once.
- Warning lights, a no-start, or intermittent electrical faults.
- Communication or module-reset problems on a scan tool.
Common causes of P0687
- Low battery voltage, poor grounds, corroded connectors, or blown fuses.
- Wiring or network (CAN bus) faults between modules.
- A module software/programming issue, or rarely a failed controller.
Useful checks before replacing parts
- Review relay command, control voltage, relay output, ignition state, battery voltage, freeze-frame data, and symptoms such as run-on or unexpected module power.
- Inspect for short-to-voltage faults, open grounds, stuck relay contacts, backfeed from aftermarket wiring, corroded relay sockets, and fuse block damage.
- Verify whether the relay control remains high when not commanded and whether PCM power feeds shut down correctly.
Related OBD-II codes
These nearby computer entries can help compare wording and pin down the fault area.