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Electric Cooling Fan Troubleshooting

Engine cooling fan

Once again, as the hot weather comes, so do "summertime problems" under the hood. One of those is the engine's cooling fan, which now likely has to work far more often than it did during the winter months, displaying problems. Troubleshooting those electric cooling fan problems can be onerous if you're not familiar with how they work and what is most likely to go wrong.

How the Cooling Fan Works

Every cooling fan works the same way: it blows air into the radiator to speed up the temperature exchange between the engine coolant and the ambient air. The fins on your radiator are designed to give off heat to the surrounding air and a fan blowing air over those fins can speed up the process, making the exchange faster and more efficient.

Electric cooling fans, which are prevalent on modern vehicles now, operate independently of the engine, turning on and off at the command of the engine control model (ECM, or computer). These fans can operate whether the vehicle is moving or not and even when the engine itself is shut off. That's why you may hear your engine cooling fan(s) running even after you've parked and shut the car down.

Because engine cooling fans can come on at any time, precautions such as removing the power source (battery connections) and keeping clear of the fan blades should be taken while working in the fan's area of the engine compartment.

The electric cooling fan (or fans) on your car have their own circuit. This power circuit starts at the battery (power source) and runs through a relay, the ECM, and to the fan. Normally, the same circuit or a parallel one will run from a temperature-controlled switch to the ECM as well. This switch tracks the temperature of the radiator or coolant (or sometimes the engine block) and opens whenever the temperature reaches a certain point, usually in the 195-degree range.

In most systems, the ECM itself controls the fan's operation using the temperature switch as one of several inputs for determining fan need.

Common Problems and How to Troubleshoot

Most problems with the cooling fan will have to do with a defect in the circuit(s) or a bad fan. The surest way to determine the issue is to do a full circuit check from one end to the other.

To test whether there is a problem with the cooling fan(s) themselves, the quickest check is to turn on the engine and let it achieve operating temperature. Then turn on the air conditioning and see if the fans kick on automatically. On most vehicles, unless a separate fan for the A/C condenser is present, the cooling fans will turn on with the A/C in order to make the cooling process more efficient.

Then, allowing the engine to continue to warm, keep it running until it reaches higher temperatures (over 200F).
You may need to rev the engine at higher RPM to achieve this. If the engine coolant reaches 200 degrees and goes beyond, to about 230, without the cooling fans engaging, you likely have a problem.

To save time, though, a good mechanic will first check the fan relay and fuses, check all electrical connections for a tight fit and that they're free of corrosion, and tests the fan motor separate from the circuit (unplugging it, applying power directly). The latter test can be done with a simple direct jump to the car's battery via jumper wires.

If the fan comes on when connected directly, the problem is likely in the circuit.