podiatra

I identified the fan relay on my 1991 firebird 5.0L. Using the test light, i find that the thin green/white stripe wire does not light up when grounded or when i test with positive(red wire).
Is that normal? if not, what could be wrong?

The fan runs only with a/c on. It does not turn on otherwise. I checked a bunch of threads but nothing in particular with the wiring.

Mad_IROC-Z

That thin green wire privides the ground for the relay to activate. Depending on which relay for which fan, the ground will either come from the computer or the temp sender for the heavy duty dual fans.

If you add a ground to that wire for testing it should make the relay work. But since your fan comes on with the AC I would say the relay works anyway. If memory serve your AC signals the computer for the fan.

Just for driving the temp sensor (near the T-stat with a yellow wire and a black wire) sends its ssignal to the computer. Perhaps that sensor is not sending the correct temp. Normally they are pretty smart and the computer will pick up on wrong readings but not always.

podiatra

Thanks, it helps a bunch.
Also, do people refers to the temp sensor as fan switch? Is it the same?

Mad_IROC-Z

The temp sensor is for the computer. There is a seperate sender for the gauge.
The fan switch would be a seperate switch located in the rear of the right cylinder head. They are used for the secondary fan in a heavy duty dual fan system.

podiatra

great...Thanks

camaronewbie

I'm assuming your car has a single fan?

If so, the fan switch located in the pass side head between #6 & #8 spark plug should be the only thing that controls the fan (aside from A/C).

The sender for the guage will be drivers side head, between #1 & #3 plugs.

Dual fan cars - the primary fan is controlled by the ECM, which gets it's temp info from the Coolant Temp Sensor usually in the thermostat housing. Secondary fan controlled by the A/C and the fan switch.

I know - it's confusing.

Fan SWITCH - pass side head - for single fan OR secondary dual fan
Coolant Temp SENDER - driver side head - for guage
Coolant Temp SENSOR - thermostat housing - for ECM

Switch = Fan
Sensor = ECM
Sender = guage

Suffering Succotash Sounds Simple!

By now, you should have pronounced the "s" sound enough to be sick of it!

podiatra

You bet... You are correct, my car only has 1 fan.
From my original posting, do you think i should the switch first, sensor, or sender?
I used a test light at the relay to test the green/white wire and i didn't get anything.

podiatra

It sounds like the problem could be narrow to the switch.

camaronewbie

Your test light won't give you anything on the relay wire that runs to the switch - it's a ground, and is only grounded when the SWITCH is at the 'fan on' temp. Your light will only light up by making a circuit - unless the fan switch is "on", your not making a complete circuit. Make sense?

Take the connection off the switch (pass side head) and ground that - the fan should come on - if it does, then the switch is bad if the car gets to avove 230 and no fan action. If it doesn't, then there is a break between the switch an the relay in that wire, or the relay is bad (which I don't think since the A/C is making the fan run).

Watch replacing that switch - coolant will spew in your face! You'll need to refill your system afterwards - after the switch swap, take rad cap off, fill radiator, run car until it gets to temp needed to open thermostat, and continue filling rad until full, then replace cap and fill the resevoir.

podiatra

THanks a lot! I know these are dumb questions... I will keep you up to date.

podiatra

I reconnect the relay back into its place.

But...i try something that somebody else suggested. I disconnected the temp sensor(next to T-stat housing) and turn on the car, apparently to see if the fan will activate. It didn't because the engine never turned on. I reconnected the sensor...guess what... the engine did not turn on. So, did i screw up something?

mantaguy

iTrader: (5)

check the coolant sensor.
1.Disconnect the coolant sensor
2.Start engine
3.The ECM should default and cause the fan to come on
4.Did it come on,if so replace the coolant sensor,if not faulty ECM,
Hope that helps,good luck.

podiatra

I did what you suggested, but the engine did not start. Then, i reconnected the sensor, and the car engine did not start. So i wasn't not able to see if the ECM defaulted.
It gave a gasoline odor to the garage too.

mantaguy

iTrader: (5)

You probably flooded it,that's what's giving you the gas odor,the sensor wouldn't cause the car not to start.Try it again in a little while.

podiatra

Mantaguy--you were correct. It turned on, actually, better than before. But the fan didn't.
I think it may be the switch??

mantaguy

iTrader: (5)

You say turned on,what the car started or fan came on?

podiatra

the car

podiatra

the car started

mantaguy

iTrader: (5)

The shop manual says if your fan did not come on then it is your ECM.
Did the fan come on when you did the diagnostics??

podiatra

no it didn't. then it may be the ECM?

mantaguy

iTrader: (5)

Before you go and start spending a lot of money on unnecessary parts,give it another test.
1.ground the diagnostic terminals A & B they are the two on the right side top two,turn on the key but don't start the car,fan should come on,if it does remove the ground from the diagnostic terminal.
2.Start the car and turn on AC,fan should come on,if the fan comes on turn off the AC and run the car until the fan comes on or until the car is almost over heating.if the fan comes on the fan circuit is OK
3.If it over heats shut the car off and disconnect the coolant sensor.
4.start the car,the ECM should default and cause the fan to come on,if the fan comes on replace the coolant sensor,if the fan does not it's the ECM.

henryd3

iTrader: (128)

If you gave the single fan, the computer has nothing to do with it. Read Camaronewbie's post back up the page. That explains it all. If your fan comes on when you turn on the AC, then your fan and relay are fine .CTS by the thermostat also has nothing to do with your fan, let it be. Find the fan switch, disconnect the wire, turn on the key and ground the wire. Does the fan come on? If so your wiring is fine. Replace the fan SWITCH and you should now be fine

mantaguy

iTrader: (5)

The cooling fan is totally controlled by the ECM based on inputs from the coolant sensor and fan control switch.The fan should run if the coolant temperature is greater than 112 degrees C (234 degrees Fahrenheit).
Now that info is for a 86 Firebird and TA,5.0&5.7 you have a 91 things could have changed and probably did.
I know the 87-89 had two fans and the coolant switch was NOT ECM related
Now I'm going on the 1 fan theory so I'm figuring it is the same as the 86.

henryd3

iTrader: (128)

Maybe in your car but not his

podiatra

Thank you all. I will change the switch. I got it, it was only 9.99. So not a big expense. As you may know from my previous comments, i am not very savvy when it comes to electric, so the switch it is easier for me, and i already identify it in the car (b/w 6,8 spar plug). I will write back tomorrow, and tell you all how it went.

mantaguy

iTrader: (5)

podiatra! You should pick up a shop manual if you plan on keeping the car,I'm not saying that to be smart or anything,You can pick one up on Ebay pretty cheap,they really come in handy.

podiatra

Thanks for the advice! I will definetely do that. Will let you know what happen with my work.

podiatra

HI all, just close out the the thread. The fan did come on around ~220 with SW500 switch from Autozone. TEMp came down to about 190 and shut off, and continue to do so.
I have ordered a shop manual as well.
Thanks for all your help--all advices were very helpful!