no coolant fans 97 firebird 5.7 V8 alt.autos.pontiac

Anyone out there have any experience with this?
Coolant fans will not run and engine will eventually overheat if left idling. If A/C is turned on, both fans will run at low speed.
I bought one new relay and sequentially put in place of each of the 3 original fan relays but it makes no difference. I did note that several times after removing the relays, the "check engine soon" lamp came on (the only time it ever did), and for just around 20 seconds, the fans ran at high speed.
I can jump around the relays and make the fans run and just for thoroughness, all fuses in the underhood fuse/relay box are good.
At this point, it's all I can think of that would easily fix this problem. Oh yeah, I did replace the engine coolant temp sensor mounted in the water pump -- again no difference.
So the question is, are there other easy/obvious things I'm missing, and if not, what are the "hard" things to examine? It's hard to imagine the PCM being at fault since everything else works properly and the car runs fine. I know that the PCM knows the coolant temperature because the car runs well cool or warm and the skip shift lamp comes on properly (only with a warm engine).
I figure you folks are the best hope I have at this point. Any help is appreciated.
FR
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did you try a fan switch. The switch falls into default mode with the a/c on which is why both fans usually run. If both fans are coming on at the same time somewhere above 230 degrees the switch in default and should be replaced.

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The components involved on this setup are just the PCM, the 3 relays, and the cooling fan motors. For low speed, relay #1 is turned on which puts the fans in series, causing both to run on low speed. For high speed, all 3 relays are turned on which puts the fans in parallel, for high speed. When the fan is running due to high engine coolant temperature (as opposed to A/C head pressure), low speed comes on at 226 degrees and off at 221, and high speed comes on at 234 degrees and off at 229.
A scan tool would help to determine whether the PCM is seeing the right coolant temperature..
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Robert Hancock Saskatoon, SK, Canada
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Frank have you tried to check out the vehicle's wiring?. I had just repaired such a problem in my Firebird. The wiring harness that feeds the high current junction box goes down the ps fender well around, and under the battery over to the fuse box. I had noticed in some Camaro and Firebird types that there are several "crimp" areas around, and under the battery where insulation may have been eroded, and the wires exposed to moisture, and weather. I believe that in your wiring harness coming from the PCM that there is a multi pin connector plug that carries the control signals for several items including the fan enable controls. The way that the fan selection works is that to engage the fans in "low speed" mode the 12 VDC control signal is sent to the "green" wire only, but to engage the fans into "high speed" mode the control voltage is supplied to both the green, and blue leads. The high speed relay circuits consist of two relays together which supplies 12 VDC to both fans simultaneously. However in low speed mode both fans are ran electrically in "series" mode which puts approximately 6 to 7 volts across each fans leads. If there is a electrical problem in either fan then the units will probably fail to function, or one fan will run significantly faster than the other. Dirt, water, or lack of lubrication in either fan can result in poor air circulation in low speed mode. However what may be causing your problem could be the electrical connection under the relays in your high current distribution box. I have observed many such problems in these vehicles. The bottoms of the relay sockets are not really insulated from weather conditions as they seem to be.

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