P0691 — Fan 1 Control Circuit Low
Moderate severityWhat it means
P0691 is stored when the engine control unit sees a fault involving the engine cooling fan control circuit. The control unit switches the cooling fan on to keep the engine and air-conditioning condenser from overheating; a control-circuit fault can leave the fan off when it is needed. A “low” reading means the signal is stuck near the bottom of its range, which usually points to a short to ground or an internally failed sensor.
Common symptoms
- The live reading sits abnormally low or at zero
- Engine running hot or overheating in traffic
- Weak air conditioning at idle
- Fan running constantly or not at all
Likely causes
- Signal wire shorted to ground
- Internally failed sensor pulling the signal low
- A failed fan motor or fan relay/control module
- A wiring, connector or fuse fault
What to check first
- Compare the live signal against a known-good range and check for a short to ground
- Confirm the fan runs when commanded with a scan tool
- Check the fan fuse, relay and wiring
Can you keep driving?
Risky in traffic — if the fan does not run the engine can overheat. Avoid stop-and-go driving until it is fixed.
Frequently asked questions
What is the most common cause of P0691?
The most likely cause is: Signal wire shorted to ground. Several other faults can set P0691 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0691 and keep driving?
Clearing P0691 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0691?
P0691 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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