85 tran am 305tpi fan wont kick on till 240 cools to 220 thinking fan switch is bad. replaced one on pass side by 6 & 8 plugs fan still kicks on at 240. where is the other fan switch location

 

If dual fans, the ECM controls the primary fan and the switch you replaced controls secondary fan. The ECM gets info from CTS (coolant temp sensor), located on intake by thermostat housing. Has 2 wires, one yellow, one black.

 

My 88 GTA had it by the front corner with the charcoal canister

 

thx i'll look for it there, mine only has one fan

 

I'm confused - didnt think there were TPI cars until 1986?

And even then the wiring diags for a 1986 TPI car don't show a fan switch, just the coolant temp sensor. Are you sure you replaced a fan switch and not the knock sensor? Fan switch was in the head, knock sensor is in the block.

Edit ... nevermind, I see that TPI started in 1985. But I don't have wiring diags for a 1985 TPI car - I assume would be the same as a 1986 car - and those don't show any fan switch in pass side head, just the CTS in the intake, so based on that the ECM must control the fan entirely.

And I'm not sure what 85Z28NOS is trying to say - there's no coolant temp anything by the charcoal canister - coolant temp needs read where there's coolant, which is in the engine - not at the charcoal canister. Maybe someone had riged a radiator probe for a fan controller into his radiator - but factory there was never any coolant temp anything by the charcoal canister

 

the guys at napa say this car has two fan switches the one i replaced on the pass side i cut the wire and put 12 volts to it and with the key off the fan will run key in on pos it wont. so i guess its a back up if the car is to hot when shutoff but not sure. the one in that controlls the ecm is in the intake by thermastat from what im told going to replace that and hopefully that will solve problem

 

Well, the fan switch on the pass side gets a GROUND, not 12v+ If you ground the wire to it, the fan will run. Putting 12v+ to that wire might fry something!

 

if you have dual fans the ECM controls the primary via the CTS, and then fan switch on the passenger side head serves as a back up or for really hot days to turn the secondary high speed fan on. the high speed fan shouold automatically come on with A/C on as well

i was always under the assumption that 85/86 TPI cars had a single electric fan which would then only be driven by the ECM via the CTS

 

This will be a little redundant at this point, but...

1985 and 1986 TPI engines had a single fan; dual fans began in 1987. But the primary operation of the single fan works the same as the primary fan in a dual fan set-up, in that the initial on/off of the fan is controlled by the ECM based on info it receives from the Coolant Temp Sensor(in the front of the intake manifold). Then the fan switch in the cylinder head serves as a back-up in both set-ups: single fan and dual fan.

The fan switch in the head turns-on the single fan(in the same way it would the dual secondary fan) by grounding-out when the temp hits 240-ish(which should never be reached under normal operating conditions), providing back-up as it was designed to do. And that's what yours is doing, so the fan switch appears to be working properly. But since the fan isn't turning-on at all until that high temp, it's also letting you know there's a problem somewhere.

But the car doesn't actually have two "fan switches" because the CTS isn't a fan switch, per se. It sends temp data to the ECM, and the ECM processes that info to use for a variety of functions, one being the primary on/off operation of the single fan(and in a dual fan set-up, for the primary fan).

The problem could be the ECM, but I'd doubt it's that, unless you're having other operational issues besides the fan. Or it could be the fan relay(located at the side of the radiator), but since the wire for the fan switch also runs through that relay, and the switch works, then the relay is probably ok too. So most-likely, the CTS in the intake manifold is at fault, as NAPA and everyone else have suggested.