Engine Control Module Power Relay Control Circuit Open
Table of contents
P0685 Possible Causes
- Weak battery Low voltage while cranking
- Faulty Engine Control Module (ECM) power relay
- ECM power relay harness is open or shorted
- ECM power relay circuit poor electrical connection
- Blown ECM fuse
- Faulty ECM
How do I fix code P0685?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Tech Notes
- Check all the Engine Control Module (ECM) fuses, if the fuses are OK, then replacing the ECM relay should take care of the problem.
Cost of diagnosing the P0685 code
The cost of diagnosing the P0685 code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0685 Description
The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The Engine Control Module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit called an Output Driver Module (ODM). The ODM output control is configured to operate as a low side driver for the powertrain relay. The ODM for the powertrain relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the powertrain relay ON, ignition 1 voltage is supplied to the ECM, and to several additional circuits.