I have a 1988 Iroc 5.7L. When I ground the ALDL both coolant fans come on.I thought only the primary ecm controlled fan was supposed to turn on.I also installed a 212 degree fan switch for the secondary fan and my gauge is in the red zone and still neither fan is turning on.Thanks for any replies.

 

I forget what I came up with explaining this but, I have a 176 temp switch for my secondary and when it comes on the primary does as well. If the primary comes on at a higher temp via the ECM..... But my car stays cool (too cool at times).

It would be nice to have a scanner so you can watch for a coolant fan request. Not everyone has a scanner though. Your MAF and coolant temp sensor (near the T-stat, yellow wire, black wire) are part of the primary fan circuit. so there is something you can check.

Now at both your realys they should have an orange wire which should be hot at all times. The primary has a brown and secondary has a tan which should be hot in run.
At the secondary relay there is a green and white wire from the temp swicth. Check it for a ground signal when the temp gets to 212. Sometimes sealant or teflon tape on the switch can get in the way of a good ground.

 

Thanks for the info.I have a test lamp and DVM so I will check it out.I might even replace the sender to the gauge.It`s possible the sender is toast and the engine is not as hot as the gauge says.