Parts
$20-200
P0685 — ECM/PCM Power Relay Control Circuit / Open
CAUTIONIs it safe to drive? Usually driveable, but get it diagnosed soon; it can worsen, hurt fuel economy, or fail emissions if ignored.
What P0685 means
A fault in the main power (ASD/ECM) relay control circuit that supplies the engine controller. Can cause stalling, no-start, or intermittent power loss.
Most likely causes (in order)
- Failed ECM/main power relay ($20-80)
- Relay socket/wiring corrosion
- Blown fuse
- PCM control driver fault
Symptoms you might notice
- check engine light
- intermittent stalling
- hard/no start
What to check first
Swap/test the ECM power relay and check its control wire and ground. Common on Chrysler (ASD relay) and others.
Repair cost & difficulty
Labor
0.5-1.5 hr
Difficulty
Moderate