P0686 code meaning
ECM/PCM Power Relay Control Circuit Low
Powertrain system Generic code P06xx codes Check engine light
What P0686 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. P0686 means the control line is shorted to ground: with the driver off it should carry battery voltage through the coil, but it sits at ground (0.5 Ω or less). The relay then stays energised and the module can no longer switch it off – after-run and shutdown are disturbed and the battery can drain. 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. The former obdex title (the wording of P0685) was a shifted entry; P0686 is the 'low' code.
P0686 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0686
- Check engine light
- Relay stays on after ignition off, battery drains
- Possibly P068B as well
Common causes of P0686
- Most likelyControl wire between relay and module chafed to ground
- PossibleRelay shorted internally or water in the relay carrier
- Less likelyModule driver shorted internally
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 P0686 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. |
| 86 | The exact fault in that area. |
What to do next
- Note P0686 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 P0686
What does P0686 mean?
P0686 means "ECM/PCM Power Relay Control Circuit Low". 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 P0686?
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 P0686 fail an emissions test?
Yes, it can. P0686 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 P0686 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0686 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.