Trouble code
P0685
ECM/PCM Power Relay Control Circuit Open
What P0685 means
The circuit controlling the main power relay to the engine computer is open.
Symptoms you may notice
- Intermittent no-start
- Stalling
- Multiple unrelated codes
- Check engine light
Common causes, cheapest first
- Failed main relay
- Corroded relay socket
- Wiring fault
- Poor ground connection
Before you buy anythingSwap the main relay with an identical one elsewhere in the fuse box as a free test. Relays are a common failure and easy to rule in or out.
What to do next
- Confirm the code with your own scan tool, or have it read free at a chain parts store.
- Decode your VIN so you know your exact engine and build date.
- Work down the causes above from cheapest to most expensive.
- Search NHTSA for a recall or service bulletin covering this symptom on your vehicle.
- Read the batteries buying guide before ordering.
P0685 is a generic OBD-II code, standardized across every make and model sold in the US from 1996 onward. The meaning is the same on any vehicle; the specific part and its location are not.
Parts
Parts commonly needed for P0685
These go to Amazon. We earn a commission if you buy, at no extra cost to you — see our affiliate disclosure. Which one you actually need depends on diagnosis — read the note above first.
Confirm fitment against your VIN on the listing page before ordering. A part that matches your year and model can still be wrong for your build date or engine code.