Radiator cooling fan does not work. How do I check for good wiring so I can fix the problem right the first time?

Radiator Fan Doesn't Run

Radiator fan failure is one of the leading causes of engines overheating, often resulting in warped aluminum heads, blown head gaskets, and damaged valves.

1. Check all under hood and under dash fuses with a test light or multi-meter:

a. Multimeter. Set multimeter to DCV, turn ignition switch to ON (Position II), touch the black test lead to ground, and touch the red test lead, in turn, to each test point on the fuse. The meter should record 12+ volts. Voltage must be recorded at each test point on a fuse; otherwise, the fuse is bad.

An alternative method, which is very fast, is to set your multimeter to audible ohms, DISCONNECT THE NEGATIVE BATTERY TERMINAL (or you could blow the fuse in the multi-meter), and touch the red and black test leads to the test points on each fuse. When you hear the meter buzz, you know the fuse is good. If your meter doesn't have audible ohms, but it does have ohms, you can still use this method--just read the meter instead. The alternative methods perform a continuity test on the fuse. Just remember to de-energize the circuits, by disconnecting the negative battery terminal, and record any radio activation codes first.

b. Test Light. Turn ignition switch to ON (Position II), connect alligator clip to vehicle ground, and touch the probe to each test point on the fuse. The test light must come on at each test point on a fuse; otherwise, the fuse is bad.

These methods allow you to accurately and quickly check all under hood and under dash fuses in several minutes, even in dark, cramped locations. They eliminate the possibility of removing and replacing the fuse in the wrong slot. Should a fuse test bad, use the fuse puller, provided in the under dash fuse/relay box, to remove it.

The radiator fan fuse is usually located in the under hood fuse/relay box.

2. Jump the radiator fan motor and ensure it runs. Disconnect the radiator fan motor connector and attach jump leads to the battery. Better yet, use a Power Probe II--it's safer, since it is fused.

3. Check/replace the Engine Coolant Temperature (ECT) Switch, not the ECT Sensor. To test the ECT Switch, remove the electrical connector. Using a multi-meter, set to ohms, check for continuity across the terminals of the switch with the engine cold. The switch should not have continuity, while the coolant is below 189 degrees F. Start the engine and allow it to reach normal operating temperature. Stop the engine and check for continuity again. The ECT Switch should show continuity, when the coolant temperature reaches 196 to 203 degrees F, and above. If the switch fails to show continuity above this temperature, replace it.

If the radiator fan runs all the time, the ECT Switch will likely show continuity below 189 degrees F. This situation will, also, require replacing the switch.


4. Check/replace the radiator fan relay, which is usually located in the under hood fuse/relay box. It's easiest to use a Power Probe II, in conjunction with a multi-meter. Power Probe II will power up the relay, while the multi-meter will test for continuity (ohms).

Cooling System Description and Operation
Cooling Fan Control
The engine cooling fan system consists of one cooling fan and one relay. The relay is powered by the battery positive voltage circuit and controlled by a switched ground from the Engine Control Module (ECM) .
During operation, the ECM supplies the ground path for the cooling fan relay through the cooling fan relay control circuit. This energizes the cooling fan relay coil, closes the relay contacts, and supplies battery positive voltage from the cooling fan fuse through the cooling fan motor supply voltage circuit to the cooling fan. The cooling fan motor is grounded through its own ground circuit.
The ECM commands the fan on under the following conditions:


Engine coolant temperature exceeds approximately 106°C (223°F) .
A/C refrigerant pressure exceeds 1310 kPa (190 psi) .
A/C is requested and vehicle speed is below 100 km/h (62 mph) with A/C pressure above 1413 kPa (205 psi) .
AF23-5 Transmission fluid temperature exceeds 130°C (266°F) .
VT25-E Transmission fluid temperature exceeds 140°C (284°F) .
When the engine coolant temperature exceeds 100°C (212°F) at key off, the fan will run for up to 108 seconds. The ECM commands the fan off under the following conditions:
Engine coolant temperature drops below approximately 100°C (212°F) .
Throttle position is greater than 95%.
Vehicle speed exceeds 113 km/h (70 mph)

Clear as mud?
Make certain the Cooling Fan fuse is good and that you have power to the Cooling Fan Relay. You should show battery voltage at the cooling fan motor when the relay is closed or jumped.