Fan 1 Control Circuit Low Voltage
The P0691 code indicates that the Powertrain Control Module (PCM) has detected a low voltage condition in the cooling fan 1 control circuit. This typically means the fan relay or wiring has a short to ground, an open circuit, or a faulty fan motor. The PCM monitors the fan control circuit for proper voltage; when it reads below the expected threshold, it sets this code. This can lead to insufficient engine cooling, especially at idle or low speeds.
1. Most Common Causes
- Faulty cooling fan relay
- Open or shorted wiring in fan control circuit
- Defective cooling fan motor
- Blown fuse or fusible link
- Failed PCM (rare)
2. Symptoms You Will Notice
- Engine overheating
- Check Engine Light illuminated
- Cooling fan not running when it should
- Air conditioning performance reduced
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the code and check for related codes.
Step 2: Inspect the cooling fan fuse and relay; test relay operation with a multimeter.
Step 3: Check for voltage at the fan connector with the engine running and A/C on; if no voltage, trace wiring for opens/shorts.
Step 4: Test fan motor by applying direct battery power and ground; if it doesn't run, replace the fan motor.
Step 5: If all components test good, check for PCM issues or software updates.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The cooling fan may not operate, leading to engine overheating, especially in stop-and-go traffic or hot weather. Overheating can cause severe engine damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor. A fan relay is cheap ($10-$30), but if the fan motor needs replacement, parts can be $50-$100 plus labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.