How to Fix a GMC Cooling Fan That's Not Working
Your engine cooling fan kicks in when the engine gets hot enough (or when the AC is running) to pull additional air through the radiator, and a fan that won't turn on can lead to overheating, especially at idle or in slow traffic where airflow from driving isn't available. This is worth addressing quickly rather than deferring.
Jump to a section: Fan relay · Blown fuse · Coolant temperature sensor · Failed fan motor · Quick reference table · FAQ
Fan Relay
The cooling fan relay switches the higher current needed to run the fan motor, and a failed relay is one of the most common and inexpensive causes of a fan that won't engage at all. Swapping it with an identical relay from elsewhere in the fuse box (temporarily, for testing) is a quick way to confirm this as the cause.
Blown Fuse
A blown fuse specific to the cooling fan circuit will prevent it from running entirely, and checking this fuse is a fast, free diagnostic step before assuming a more expensive component has failed.
Coolant Temperature Sensor
The engine computer relies on the coolant temperature sensor to know when to trigger the fan, and a failed or inaccurate sensor can prevent the fan from ever receiving the signal to turn on, even though the fan motor itself is perfectly healthy. A scan tool can compare the sensor's reported temperature against expected values to check this.
Failed Fan Motor
If the relay, fuse, and sensor all check out but the fan still won't spin, the fan motor itself has likely failed. This is generally the least common of the four causes but does happen, particularly on higher-mileage vehicles.
Quick Reference Table
| Step | What To Check |
|---|---|
| 1 | Check the cooling fan fuse |
| 2 | Test/swap the cooling fan relay |
| 3 | Check coolant temperature sensor readings |
| 4 | Test the fan motor directly if all else checks out |
Frequently Asked Questions
Is it safe to drive if my cooling fan isn't working?
Highway driving may be okay short-term since airflow from motion helps cool the radiator, but idling or slow traffic risks overheating quickly without a working fan, so it's best to get it diagnosed and fixed promptly rather than continue driving normally.
How do I know if it's the relay or the fan motor?
Swapping in a known-good relay (temporarily, from an identical spot in the fuse box) is a quick test; if the fan works with the swapped relay, the original relay was the problem rather than the motor.
Can a bad temperature sensor really stop the fan from running?
Yes — if the sensor reports a temperature lower than the engine actually is, the computer never receives the signal to trigger the fan, even though every other component is functioning correctly.
Will my AC still work if the cooling fan is broken?
Not properly — many vehicles also rely on the cooling fan running when the AC compressor is active, so a failed fan can affect AC performance as well as engine cooling.
Shop the Parts Mentioned
- Summit Racing Fuses — for replacing a blown cooling fan fuse.
- Engine Coolant Thermostat — worth checking alongside cooling fan issues during overheating diagnosis.
- Bidirectional Scanner — checks coolant temperature sensor readings and can command the fan for testing.
- Wireless Scanner — checks for related engine cooling and temperature codes.
- 95-Piece Mechanics Tool Set (Metric & SAE) — for fan relay, fuse, and motor access.