What P0690 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.
How the engine computer detects it
P0690 means the sense voltage is too high: voltage is present although the relay has been off for 2 s – a welded or sticking contact, or external voltage fed in through a short – or, on some systems, overvoltage above 18 V with the relay on. GM sets it at 4 V or more with the relay off, in 50 of 63 samples at 100 ms, lamp after two trips; GM Europe's 2.0 L turbo above 2 V with the relay off or above 18 V with it on, for 2 s, and advises fixing other short-to-voltage codes first. Modules, fans or pumps may keep running after switch-off and the battery drains overnight.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light
- Module, fan or pumps keep running after ignition off
- Battery drains overnight
Common causes
- Relay contact sticking or welded Most likely
- Short to voltage on the sense or load line (external feed from another component) Possible
- Control wire shorted to ground (relay permanently on) Possible
- Overvoltage from the alternator regulator (where the 18 V limit applies) Less likely
How to diagnose P0690
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: ecm power relay, relay control circuit, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 6
- Computer and output circuits
- 90
- Specific fault
Questions drivers ask
Can I drive with code P0690?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0690?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0690 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0690 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.