P0685 code meaning
ECM/PCM Power Relay Control Circuit/Open
Powertrain system Generic code P06xx codes Check engine light
What P0685 means
The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. P0685 means the relay control circuit is open: GM measures with the driver off and flags 200 kΩ or more to ground. GM checks with run/crank voltage above 11 V and sets the code after 8 of 10 samples at 250 ms, with the lamp after two trips. GM Europe's 2.0 L turbo compares commanded and actual state for 2 s, Ford's 2023 diesel checks continuously within 0.5 s. A real open keeps the relay from pulling in – no start; on Saab's V6 there is then no communication with the engine module and the MIL flashes. GM notes P0686 may set alongside.
P0685 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0685
- Check engine light
- Engine does not start or stalls
- No communication with the engine module (Saab)
- MIL flashes rapidly, other relays click (Saab)
Common causes of P0685
- Most likelyOpen or corroded control wire between relay coil and module or connector
- Most likelyRelay coil open or relay badly seated
- PossibleRelay coil supply missing (fuse, battery positive)
- Less likelyWeak battery or voltage dip
- Less likelyModule driver faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
ECM power relayRelay control circuitEngine control module
What each part of P0685 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6 | Area: computer (engine control module) and output circuits. |
| 85 | The exact fault in that area. |
What to do next
- Note P0685 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0685
What does P0685 mean?
P0685 means "ECM/PCM Power Relay Control Circuit/Open". The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. It is a generic code, so it means the same on every make.
Is it safe to drive with P0685?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0685 fail an emissions test?
Yes, it can. P0685 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0685 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0685 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.