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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.
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