Fan 2 Control Circuit Low

What it means

The engine computer (ECU) controls cooling fan 2, which on many vehicles is the second fan or the higher fan speed, through a relay or control module. The computer detected lower than expected voltage on its control circuit, so the vehicle may lose part of its cooling capacity when it is needed.

Related codes: P0694P0691P0480P0481P0645

Symptoms4

• Engine temperature rising in traffic or with the A/C on in hot weather.
• Weak A/C cooling while stopped.
• Second fan running constantly on some vehicles.
• Check engine light on.

Possible causes5

• Fan 2 control circuit wire shorted to the body or ground.
• Internally damaged fan 2 relay coil.
• Faulty fan control module on vehicles that have one.
• Moisture or corrosion in fan or relay connectors.
• Faulty control circuit inside the engine computer (rare).

How to diagnose5

1. Turn on the A/C, let the engine warm up and check whether the second fan or high speed engages.
2. Use the scan tool to command fan 2 on if the function is available.
3. Identify the fan 2 relay from the manufacturer wiring diagram and swap in an identical known-good relay.
4. Test the control wire's isolation from ground with both ends disconnected.
5. Inspect connectors for melting or corrosion.

How to fix5

1. Replace the fan 2 relay if its coil is damaged.
2. Repair the wire shorted to ground and re-insulate and secure it.
3. Clean or replace corroded connectors.
4. Replace the fan control module or fan motor if proven faulty.
5. Clear the codes and confirm both fans run when needed and the code does not return.

The cost is low for a relay or wire repair, and rises if a fan control module or new fan motor is needed.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions