GM Cooling Fans That Won't Shut Off

Written by richard rowe
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GM Cooling Fans That Won't Shut Off
GM cooling fans may fail to shut off for a few reasons. (Scott Olson/Getty Images News/Getty Images)

Cooling fans are basically just direct current electric motors with blades attached to the output shaft. The motor receives current from the power box or thermostat, the fan activates and spins to draw air in through the radiator. Diagnosing a failure to stop is actually a bit easier than diagnosing a failure to run, primarily since so few things can cause it to happen. GM products are just like any other when it comes to cooling fan issues, so the basics of troubleshooting a malfunction will apply to most any vehicle with an electric cooling fan.

Skill level:
Moderately Challenging

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Things you need

  • Basic hand tools
  • New fan relay

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  1. 1

    Locate the cooling fan's relay or fuse and remove it. Turn the ignition on or start the car. The fan should shut off; if it doesn't then you have a crossed wire somewhere between the fan's power supply and the fan itself. Track the red or white wire powering the fan and locate the source of the crossover.

  2. 2

    Plug the new relay into your power box. You could test the relay with a digital multimeter, but it's not worth the trouble. Relays do wear out and stick open or closed, so the odds are good that this is the source of your failure. Even if your old relay still works, taking this opportunity to replace it is just good preventive maintenance.

  3. 3

    Check the connections between your coolant temperature sensor and the wiring harness. Over time, the terminals can work loose and corrode, causing the computer to think that the engine is running hotter or colder than it should. A loose connection or corroded terminals will likely cause your temperature gauge to read higher than it should, so consider this a symptom. If you find a loose connection then unplug the harness, clean the terminals with a wire brush and plug it back in.

  4. 4

    Replace the coolant temperature sensor or thermostatic fan switch. If the fault isn't in the wiring or the connection, then this is the only other possible cause for undesired power delivery. A bad coolant sensor or thermostatic fan switch will exhibit the same symptoms as a bad connection, so keep an eye out for improper gauge function or a check engine light. The fault could theoretically be in your engine control computer, but the odds are that a failure of this sort will have manifested in more serious ways.

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