Thread: cooling fans on 90 G.P.

Make sure someone hasn't hard-wired the fan. Make sure there isn't a short behind the fuse panel. Get a wiring schematic for the car. ALLDATA is a great place to start.

1) Does the fan shut off when you remove the relay?

The relay receives a low current signal from some control circuit, either a sensor or the ECM, and this activates the relay coil. It's just a switch which in turn completes a high current circuit within the relay. This is the way our cars keep high current circuits in check. Low voltage signals from anywhere in the system to a centralized high current location (fuse/relay box).

2) If the fan stays running with the relay pulled then the fan is either hard-wired or there is a major short somewhere on the motor + wire.

3) If the fan does in fact shut off with the relay removed then check that the relay control signal isn't shorted to a supply somewhere in the system. To test the control wire, disconnect the battery and pull the relay. Check continuity from the relay control pin to the + battery cable. It should be open or very high resistance. If there is 0.5 ohm or less then the wire is shorted to 12V somehwere in the system; possibly behind the fuse/relay panel.

4) If it's getting the signal from the ECM then you have a real problem. That's, of course, if the OBDI is actually designed to control it. Someone may have flashed the EPROM incorrectly. You'll have to have someone reflash it or get a OBDI tuner kit. The ECM could be defective also.

How long have you had the car? A little history is always helpful.

Start here with the ECM

http://i1255.photobucket.com/albums/...ECM-Pinout.jpg

It looks like the ECM does in fact control the fans. The ECM is also interfaced with an AC control module somewhere in the car. The AC control module may be your problem with the driver's side fan. It's a dealer part and it's very expensive. Junk yard may be an option.

There is an auxillary fan controller available. It requires splicing into the AC compressor control wire to turn on the fans. It comes with the neccesary wiring and a thermostat that mounts on the radiator or on the engine block.

NOTE: This wouldn't explain why the passenger fan stays on; unless there are separate relays for the fans that you are unaware of. Keep looking for a short in the motor + wire if you're sure the fan stays running without the relay.

Question: Are there two relays; one for each fan?

first of all,thank you for the ECM pinout! the 90 grand prix LE 3.1 has 3 relays in eng. compartment passenger side inner fender,one relay for each fan and a relay for the A/C cluch, i've changed all 3 relays.I'm trying to find out now if there ain't another switch that controll's the fan's.I've read on one post that there was one on the back head on driver side with one green wire comming from it BUT it was on a newer GP with the 3.1,I believe 93 or 95 somthing like that.I also read the ECM sends the signal to the relays witch in turn controlls the operation of the fans.I was thinking of replacing the EMC with one from the bone yard!! If i do replade the ECM would i need to have it reprogramed? What if i can get one from the same yr.and eng.size, would IT need reprogramed?

If you have definately pulled the relay that controls that particular fan then I believe the fan should turn off. I doubt that there is another high current circuit for the fan. The fans may be turned on at different times for different reasons, all of which are via the relay. You say that the ECM controls the fans via the relay. Why is it still running without the relay? There is probably a short somewhere on the + motor wire as mentioned previously. We cannot determine wether or not the ECM is faulty at this time. So do not possibly waste your money on another ECM.

Don't worry about the temperature sensor that is somewhere on the motor. It's just a generic switch that tells the ECM if the engine temperature is above a certain value like 225 degrees. This leads us back to the same problem; even if the temperature is above the pre-determined value we can't tell if the ECM is actually sending a signal to the relay because the fan is hard-wired or shorted.

I'll get some more schematics that might shed some light on the fan circuits and how they interact with the rest of the system. The fan relays may actually be grounding switches. This means that there may always be power to the + motor wires and the relay completes the ground circuit. A good test would be to remove the connector from the fan that is working and see if there's 12 volts on the + motor wire when the car is off and key in the "on" position. This will tell us if the fans are controlled by the relay as a ground return.

In the mean time trace the wires for the fan and make sure there's nothing shorted.

OK here is the exact ECM pinout for the 3.1L V6 (though it was a I4)

Here is the body wiring diagram for a 1991 Grand Prix...should be the same for 1990.

I know that the body diagram is difficult to understand but you have find out which VIN your car is and follow the schematic.

There are four possible VIN's:
1) VIN L
2) VIN T
3) VIN 4
4) VIN X

Well i did find someone had the fan wired direct to a hot wire.I rewired the passenger fan back the way it's supposed to be [black wire to black wire and orange with black stripe to orange with black stripe]on both driverside and passengerside. Now the passenger fan no longer stay's on, but it don't come on at all and the one on the driver side is acting like the auxilliary fan[passenger side]fan. It comes on at 225deg. and goes off around 180deg.shouldn't that be the A/C fan[auxilliary]passenger side? They seem to be in the reverse order!!! Oh they can't be pluged in backward on the ECM, they can only plug in to matching outlet.This realy is a puzzle.The A/C cluch don't kick on either [probably no freon] but i wouldn't think that would cause the reverse fan order.Any idea's? CORRECTION the wire's going to the fan might be red with black stripe, and not orange with black stripe.

I kind of thought the fan was hard-wired.

Your PCM senses that the AC is not working (AC pressure sensor). Fix the AC and the fan will turn on. Who cares which fan is coming on, as long as the fans come on. Without the AC on, one should come on at 225 and the other should come on at 235 or something. The engine may not be hot enough to turn both fans on yet.

Look on the back of the fuse/relay panel and see what ECM AC control wires are going to which fan relay.

Dark Green/White = Fan 1 relay
Dark Blue/White = Fan 2 relay

I don't know which fan is 1 or 2, driver's side or passenger side.

Come back and see us again.

Do you have DTC codes P045X or P044X?

What to do:

Get rid of vented cap
Make sure solenoids are working (purge and vent)
Temporarily bypass the canister
Make sure vacuum lines aren't clogged and purge lines are good

Run it and see what happens.

There should be no difference in AC control between defrost and cabin cooling. The AC system is designed reach a certain system pressure and/or head pressure and that's it. Cooling is controlled by redirecting air, hot and cold, within the cabin.

Some of the newer compressors have a built in bypass that prevents excess head pressure. They did this to prevent premature clutch wear. I don't know about the dinosaur that you are working with.

I would bite the bullet and just change the pressure sensor. You're almost there. Don't muck it up over a sensor. If the system is cycled on/off via pressure sensor input then not changing it may damage the compressor or cause leaks. Peace of mind is worth it's weight in gold, no?

1989 T/A 3.8L Turbo - Component location