OBD-II Generic Automotive Error Code P0685: How to Fix It

Q: Can I drive with error code P0685?

It is not recommended. The ECM/PCM controls engine operation, and a fault in its power relay can cause stalling, poor performance, or no start. Driving may leave you stranded or cause further damage.

Q: What causes P0685?

Common causes include a faulty ECM/PCM power relay, blown fuse, corroded or loose wiring in the relay control circuit, or a defective ECM/PCM.

Q: Will replacing the ECM relay fix P0685?

Often yes, if the relay is defective. However, the underlying issue could be in the wiring or the ECM itself. Test the relay and circuit before replacing parts.

Q: How much does it cost to fix code P0685?

DIY cost is under $20 for a relay and fuse. If you need professional diagnosis, expect $75-150 for labor plus parts if the ECM needs replacement ($300-$1000).

Q: Is P0685 the same for all car makes?

Yes, P0685 is a generic OBD-II code, so the meaning is the same across all vehicles (e.g., Ford, Chevy, Toyota). However, the relay location and wiring colors may vary.

Abstract

Error code P0685 indicates a problem with the ECM/PCM power relay control circuit. The engine control module has detected an open or short in the relay circuit that powers the computer. This can cause the engine to not start or run poorly. The severity is medium, as it may leave you stranded but typically won't cause immediate catastrophic damage.