What it means
Cooling Fan 1 Control Circuit Low: the control-circuit voltage is below the expected range. Reduced cooling-fan control can let the engine or A/C condenser overheat.
At a glance
- Usually lights the check-engine light
How it works
The engine controller monitors the low-side control circuit for Cooling Fan 1, which operates the primary engine or condenser cooling fan on vehicles using this circuit. P0691 sets when the monitored control voltage is below its expected range, often because the control wire is grounded or the fan relay circuit has a fault.
Common causes
Most likely first.
- Fan relay defective
- Wiring shorted to ground
- Connector pins corroded - high contact resistance
Symptoms
- Cooling fan may not operate as commanded
- Engine or A/C condenser may overheat
How to diagnose it
- Record freeze-frame data and check coolant temperature, A/C request, and Fan 1 command data to learn whether the controller was requesting the fan.
- With the engine cool, inspect Fan 1 wiring, connectors, relay socket, and ground-side control wire for corrosion, loose pins, or contact with ground.
- Use scan-tool output controls, if available, to command Fan 1 and observe whether it runs and whether the circuit fault returns.
- Test the Fan 1 relay and its control circuit according to the manufacturer's wiring diagram and procedure.
- Check for an unintended short to ground in the Fan 1 control wire and verify the controller output only as directed by the manufacturer.
Common fixes
- Clean and secure corroded Fan 1 connector or relay-socket terminals.
- Repair a Fan 1 control wire shorted to ground.
- Repair damaged or chafed wiring in the Fan 1 circuit.
- Replace the Fan 1 relay if it fails the specified test.
Can I keep driving?
Avoid driving if the temperature gauge rises, the engine overheats, or A/C operation causes temperatures to climb; switch off the A/C and stop safely if overheating begins. Continued overheating can damage the engine.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.