I have an 88 Iroc with dual coolant fans.I have ran every test in the GM factory service manual and everything checks out but when the car is actually running the gauge is in the red and neither fan turns on.I even replaced the secondary fan switch with a 212 degree turn on temp and still no fans.Am I overlooking something very simple.Thanks for any replies.One thing I found confusing was in one part of the book it says when you ground the ALDL the fan should turn on and in another part of the book it says check ECM for diagnosis.

 

When you turn on the AC while the car is running, does one of the fans turn on? If not perhaps you have a relay or wiring/connections to them problem

 

Do the fans come on under any testing conditons?

Super quick test: There is a high pressure switch on the AC line, located near the passenger side strut tower. Pull the 2 pin connector, jump the wires with a paper clip and turn the ingition to "run".

I don't know if you want to use a 212* switch for secondary fan. The secondary fan is going to run a lot. Factory switch closes to ground at 238*.

 

I jumpered the high pressure switch(black and gray wires) and the secondary fan came on.The A/C does not work though.All the tests seemed to check out OK so it seems either the primary is not coming on because it is not getting a signal from the ECM(but if you ground A and B on the ALDL it comes on) or the fan switch is toast for the secondary fan.I replaced the coolant sensor and the sending unit to the gauge in the dash.Other than that the only thing I can think of is the gauge in the car is totally out of whack.

 

Screw the factopry setup, get a seperate fan controller that probes the radiator and is adjustable, and be done. I hate the factory setup, never works right and everyone always has problems. I installed a Flex-a-lite controller years ago, best $100 I ever spent! Uses it's own wiring, so you don't need any of the factory junk, easy 45minute install. Your ECM won't care a bit!

 

That is personal opinion.
ECM will run the primary @ 220 regardless.

 

I have this same exact problem with the 87 IROC I put together. Relays are good, gauge sender is new, fan switch is new, CTS is new, fans turn on when tested. I figure the gauge is off as well. I have a new 180 thermostadt in it and the gauge says 220 while cruising on the hwy. Need to get a good scanner and see what the CTS is telling the ECM.

 

I would say that your gauge is reading wrong. This is very common in our cars. My gauge in my iroc says about 180 cruising down the road and it will read about 240 when the fan kicks on at idle. I would test your temps with an aftermarket gauge. That way you will know if you have problems with your system.

 

That is probably what it is.I got a gauge from a wreckers removed the old one and installed the one from the wreckers and it read exactly the same.In the red and no fans.What you suggest is more than likely to give a more accurate reading.I wish I had an OBD1 scan tool so I could see what the CTS is sending the computer or an infrared thermometer.The gauge must be way out because I have a 212 degree fan switch installed and still no fans.For the time being I ran a wire from the gray wire on the A/C high pressure switch to a toggle switch in the car.When I throw the switch with the key on(engine not running)the secondary fan turns on.If the engine is running both fans turn on.

 

If you had infrared thermometer, what would you use/aim at to read temp? The thermostat housing?

 

Temp gauge is my problem. I let it get hot today and the primary fan turned on once the gauge was PAST 260. Coolant wasn't boiling. 50/50 mix

 

If I had one I would aim it as close as possible to the temp sender in the head or where the CTS screws in.It may not give an exact reading but it may give an indiction how far out of whack the gauge is.

 

I would have to agree. I run an aftermarket setup as well and don't have to screw around with the stock setup anymore. No more toggle swtiches, swapping switches, etc. It just works now. I would recommend the Dakota Digital setup as it is a cleaner install than than the probe in radiator types.

 

http://www.chevythunder.com/fuel%20i....%20pg%20C.htm