P0691
UniversalFan 1 Control Circuit Low. This code indicates that the Powertrain Control Module (PCM) has detected a low voltage condition in the control circuit for the primary cooling fan.
Medium SeverityThis code signifies a low voltage problem within the circuit that controls your vehicle's cooling fan. This issue can prevent the fan from operating correctly, potentially leading to engine overheating, especially in slow traffic or hot weather.
⚠️ Before You Begin (Safety First)
Always ensure the engine is cool before working on the cooling system. Disconnect the battery before checking any electrical components or wiring to prevent accidental fan activation or electrical shorts. The cooling fan can activate unexpectedly.
Common Symptoms
- Check Engine Light illuminated
- Engine overheating (especially at idle or low speeds)
- Cooling fan not running
- Reduced air conditioning performance
- Engine temperature gauge reading high
Common Causes
- Faulty cooling fan control relay
- Open or short in the cooling fan control circuit wiring
- Defective cooling fan motor
- Corrosion or poor connection at electrical connectors
- Faulty Powertrain Control Module (PCM)
Frequently reported on: General/Universal, Ford F-150 (2004-2014), Honda Civic (2006-2011), Chevrolet Silverado (2007-2013)
Diagnostic Steps
- Inspect fuses related to the cooling fan in both the under-hood and cabin fuse boxes for continuity.
- Locate and test the cooling fan relay; you can often swap it with a known good relay of the same type (e.g., horn relay) to see if the fan operates.
- Visually inspect the wiring harness for the cooling fan for any signs of damage, fraying, or loose connections from the PCM to the fan and relay.
- Check the electrical connector at the cooling fan motor for corrosion, bent pins, or damage.
- With the engine off and cool, manually spin the fan to check for any binding or resistance, ensuring it moves freely.
👨🔧 When to Call a Professional
If after checking basic components like fuses and relays, the issue persists, or if you suspect a complex wiring harness problem or a faulty Powertrain Control Module (PCM), it's best to consult a professional automotive technician. Complex electrical diagnostics require specialized tools and expertise.
Commonly Asked Questions
Can I drive with a P0691 code?
It's not recommended to drive for extended periods if your engine is overheating. Short trips might be acceptable if you monitor the temperature closely, but repair should be done promptly to prevent engine damage.
Is it safe to replace the cooling fan relay myself?
Yes, replacing a relay is typically straightforward and safe, provided you follow proper safety precautions like disconnecting the battery before handling electrical components.
Could a bad cooling fan motor cause P0691?
Yes, if the fan motor has an internal short, excessive resistance, or draws an incorrect amount of current, it can cause the PCM to detect a low voltage condition in the control circuit and trigger this code.
What's the difference between Fan 1 and Fan 2?
Many vehicles use two cooling fans or a multi-speed fan system. Fan 1 typically refers to the primary or low-speed cooling fan, while Fan 2 might be a secondary or high-speed fan, or specifically for the AC condenser cooling.
How do I test the cooling fan motor directly?
You can often test the fan motor by disconnecting it from the vehicle's harness and carefully applying direct battery voltage to its terminals. Ensure you identify the correct polarity to avoid damage before performing this test.