P0691: Fan 1 Control Circuit Low
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 circuit is shorted to ground or has excessive resistance. The PCM monitors the voltage on the fan control circuit; when it falls below a calibrated threshold, this code is set. Common causes include a faulty cooling fan relay, a defective fan motor, wiring issues (shorts, opens, or corrosion), or a failed PCM.
01. Most Common Causes
- Faulty cooling fan relay
- Shorted or open wiring in fan control circuit
- Defective cooling fan motor
- Corroded or loose electrical connectors
- Failed PCM (rare)
02. Symptoms You Will Notice
- Engine overheating
- Check Engine Light illuminated
- Cooling fan running continuously or not at all
- Reduced air conditioning performance
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0691 and check for related codes.
Step 2: Visually inspect the fan 1 wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the cooling fan relay and fan motor operation using a multimeter or by applying power directly.
Step 4: Check for shorts to ground or opens in the control circuit between the PCM and the relay/fan.
Step 5: If all else is okay, test the PCM output or consider PCM replacement as a last resort.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, as the cooling fan may not operate properly, leading to engine overheating and potential damage.
How much does it cost to fix?▼
The cost to fix P0691 typically ranges from $50 to $150 for parts and labor, depending on the root cause (e.g., relay, wiring repair, or fan motor replacement).