What P0689 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
P0689 means the sense voltage is too low although the relay is commanded on – the contact does not close or has high resistance, the sense line is open or grounded, or a fuse in the load circuit has blown. GM sets it at 5 V or less with more than 9 V supply in 5 of 6 samples at 1 s, lamp after two trips; GM Europe's V6 below 6 V for 1 s and the 2.0 L turbo below 5 V, both without the lamp. GM includes an open sense line here. Starting problems or stalling follow, and on Saab the throttle control, which uses this voltage, may go into limp mode.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light (depending on the maker)
- Starting problems or no start
- Engine stalls or stumbles
- Possibly electronic throttle limp mode
Common causes
- Relay contact burnt or not closing, relay faulty Most likely
- Fuse in the relay load or sense path blown Possible
- High resistance or corrosion in relay carrier, connector or wire Possible
- Weak battery Less likely
How to diagnose P0689
- 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
- 89
- Specific fault
Questions drivers ask
Can I drive with code P0689?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0689?
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 P0689 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 P0689 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.