When an electric radiator fan does not turn on, the cause is usually a blown fuse, a failed relay, a worn fan motor, a bad coolant temperature sensor or a wiring fault. On trucks with a belt-driven fan, a worn fan clutch does the same thing. The usual result is overheating in traffic or at idle while the engine stays cool at highway speed, because moving air through the radiator does the fan’s job at speed.
Common causes
- Fuse or relay: check the fan fuse and swap the fan relay with an identical one from the fuse box.
- Fan motor: worn brushes or a seized motor; it may run if tapped, which confirms the motor is failing.
- Coolant temperature sensor or switch: the computer never sees the temperature that should turn the fan on.
- Wiring and connectors: corrosion or a broken wire at the fan connector.
- Fan clutch (mechanical fans): a clutch that slips no longer pulls enough air at idle.
Quick checks
- With the engine warm, turn on the air conditioning; on many vehicles the fan should come on with it.
- Check the fan fuse and relay.
- Inspect the connector at the fan and the wiring for damage.
- Read codes for coolant temperature sensor or fan control faults.
Keep your hands clear of the fan; electric fans can start without warning even with the engine off on some vehicles.
Electric fans vs fan clutches
Most cars use electric fans switched by the engine computer or a temperature switch. Many trucks use a belt-driven fan with a viscous fan clutch that locks up as the air behind the radiator gets hot. A clutch that spins freely by hand with the engine off and cold, or one that leaks fluid, is usually worn.
Fan runs all the time?
A stuck relay, a faulty temperature sensor or the air conditioning being on can keep an electric fan running; some fans also run briefly after shutdown by design.
Why it matters
A fan that does not run lets the engine overheat in traffic, and repeated overheating damages head gaskets and cylinder heads; see engine overheating. If the fan runs but the engine still overheats, check the coolant level, thermostat and water pump; see bad water pump and thermostat symptoms.
Fans and radiators for the Corvette
For the C5, C6 and C7 Corvette we carry DeWitts radiators and radiator-and-fan combos, plus a SPAL fan listed for the C7 with a 70mm DeWitts radiator. See the DeWitts page and Corvette parts.
More guides: car overheating when idling · bad radiator symptoms.
Trouble codes: P0691 Fan 1 Control Circuit Low · P0692 Fan 1 Control Circuit High · P0693 Fan 2 Control Circuit Low · P0694 Fan 2 Control Circuit High · P0480 Cooling Fan 1 Control Circuit · P0481 Cooling Fan 2 Control Circuit · all OBD2 codes.
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