Radiator Fan Turn-On Switches
After performing all necessary checks, you've determined that the radiator
fan turn-on switch on a late model GM car is not functioning properly. With
the replacement fan switch in hand, you study the engine compartment in
an attempt to locate the faulty part. You spot a switch that looks like the replacement. Pulling the connector
off, the electrical contacts look just like those on the new switch. Within
seconds, the new fan switch is installed, but the wire connector doesn't
fit into the switch! What went wrong? You replaced the wrong switch. The GM car you are working on has a radiator
turn-on fan switch that looks almost identical to the coolant temperature
sensor. But if you compare the sensor you just removed to the new fan switch,
you'll notice three important differences.
First, the radiator fan turn-on switch has a larger hex-head than the coolant temperature sensor.
Second, the coolant temperature sensor has two electrical connections, while the fan switch only has one. The inside of the plastic sleeve of the coolant temperature sensor is lined with metal and is actually a second electrical connector.
Finally, the wiring harness connector to the coolant temperature sensor has two wires, the wire harness connector to the fan switch only has one (see illustration below).
Radiator Fan Turn-on Switch Assembly
How can I tell the switches apart if I can barely see the switches under all that electrical wiring?
Easy! Just plug your scan tool into the ALDL connector and turn on the key. Punch in the coolant temperature sensor reading and disconnect the switch you believe is the radiator fan turn-on switch.
If the temperature reading for the CTS stays the same when you disconnect the switch, you've indeed found the fan switch. If the CTS reading falls to -40°F, you've disconnected the wrong switch.
If you do not have a scan tool, keep looking until you find the switch that has only one wire.