Jim Grant's Tech Tips

‘90 Pontiac Sunbird Turbo 2L., Inoperative Cooling Fan
Q: The radiator cooling fan will not come on when the motor heats up on my ‘90 Pontiac Sunbird Turbo with a 2L engine. I replaced the heat sensor, but still had the same trouble. I found the fan relay was not operating, yet the relay will operate if I apply a ground. Any ideas?..... Bob

A: The relay for the cooling fan is controlled by the vehicle’s computer. For the computer to activate the cooling fan it looks for information (inputs) that it interprets as a need to turn the cooling fan on or off. It’s all part of that "if this, then that" programming stuff. The coolant temperature sensor is one input that is often confused with the coolant temperature sender and wrongly replaced. The sender is for the gauge and the sensor is for the computer, big difference. Also the computer will turn the cooling fan on if it sees that the A/C has been turned on. If you were to come into our shop this is how the diagnosis would go. The first thing would be to turn the A/C on to see if the cooling fan comes on. If not then, the cooling fan relay would be identified and then by-passed. If the fan worked then the relay, wiring, computer or computer inputs would be of concern. If the fan did not work, the wiring power supply (fused link) and ground, and fan motor would be checked. A word of caution, when probing the wiring at the relay contacting the wrong wire at the right time "will" let the magic out (ruin the computer) of the vehicle’s computer and add $100 to $200 more dollars to your cooling fan problem.