Troubleshooting electric cooling fan performance

Electric cooling fans became popular with the introduction of front-wheel-drive and the relentless goal of improving fuel economy.


Computer-controlled fans engage according to inputs like the engine coolant sensor and vehicle speed sensor, just to name a few. This allows closer control of engine temperature, but also complicates the diagnostic process because the computer itself is now involved.

Some things to keep in mind:

• Ford uses integrated controllers on some of its models to control a number of functions, including the cooling fan. Rather than a stand-alone relay, the controller may contain a number of relays inside. For the exact layout and designation of the inputs to and outputs from the controller, consult a reliable shop manual.

• It's wise to understand the exact fan strategy designed into a given vehicle. For instance, some fans turn off automatically at a certain road speed because airflow at that speed makes fan operation no longer necessary. If you didn't know this, you could wind up trying to track down the reason a fan doesn't work at road speeds.

• More than ever, a scan tool can play a vital role when pinpointing circuit woes. By commanding the cooling fan through the powertrain control module (PCM), you can quickly determine that much of the circuit is working properly. This can eliminate some of the required testing using with jumper wires and other circuit bypass techniques.

Once you've made necessary repairs, leave nothing to chance and run the vehicle to make sure the fan operates properly in all modes. That way, you know the car and your customer will both keep their cool.

Be sure to check out more on troubleshooting electric fans in our Diagnostic Review.

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