Fan Overspeed

Possible causes

• CommonFailed fan motor
• CommonFailed fan relay or control module
• CommonBlown fuse on the fan circuit
• CommonCorroded connector or damaged wiring
• PossibleDebris jamming the fan
• PossibleCorroded earth at the fan
• RareFailed control module driver
• CommonFan control circuit failed to full output
• CommonFan speed feedback signal lost

What you might notice

• Cooling fan running at full speed constantly
• Very noisy at idle
• Fan running after the ignition is switched off
• Battery draining
• Check engine light on

What to check, in order

1. Check whether the fan is genuinely running flat out, or whether the module has simply lost its speed feedback.
2. If the fan runs after switch-off and will not stop, pull its relay or fuse rather than leaving the car standing - it will flatten the battery.
3. Check the fan control module and its wiring.
4. Watch the temperature gauge in slow traffic and stop if it climbs. A fan fault shows itself when the car is stationary and clears at speed, because airflow through the radiator does the fan's job - that pattern is the clearest evidence available and costs nothing to observe.
5. Check whether the fan runs at all when the engine is hot or the air conditioning is on.
6. Check the fuse and swap the relay with an identical one from elsewhere in the box.
7. Inspect the connector and the fan earth for corrosion.
8. Check for debris in the fan and that it spins freely with the engine off and cool.