Cooling fan will not come on (PLEASE HELP !!)

[RAR]

Hello,

I just bought a 95 3.4L 5-speed firebird, and the thing is overheating because the fan will not come on.

I haved looked at it this weekend and have found:

1. The fan will work if power is applied directly to the two terminals.

2. The relays function as expected (per the procedures in the Hanes manual)

3. Swapping relays with the AC compressor (same part number) also, does not resolve the probelem

4. The thermastat is working properly - opens about 195 or so - check by reading the temp at the radiator

5. Replaced and checked the coolent sensor on the intake manafold - near the thermostat - tested good (read about 2200 ohms at room temp, and 250 ohms at 180 or so - this is what the Hanes manual said it is should be).

6. Checked the power to the coolent sensor - read 5.0 volts

7. One side of the relay (one of the switch sides) reads 12V always - when I short this to the other switch terminal the fan will turn on.

8. Traced the wire back to the computer and it makes good contact - checked continunity while moving the different wires - to check for intermitant problems.

With all of this the Hanes manual is out of suggestions - could it be a blown circit on the ECM - this is OBD I, but it does not show any codes.

On a related note: if I have to replace the ECM, about how much are they going for and what is a good place to get them. Also does the manual / AT have the same ECM? What about different cars with a 3.4L (FWD/RWD?) or Camaro / Firebird / S10 ?

Thanks in advance

Richard

[John_D.]

I believe there are two temperature sensors. One for the gauge and one for the ECM. I'm not sure which one you tested...

Also if the coolant level is low, the temp sensor will not report the correct temp back to the ecm.

Will the fan come on when you turn the a/c on?

[RAR]

Thanks,

I checked the one used by the ECM. I did not check the gauge one (it only has one wire and sits behind the spark module) because gauge apears to be correct (somwhat verified by reading the temp of the water in the radiator).

I did not know about the fan comming on when you have the AC on until now. I will give that a try tonight. - so basicly if the AC is on the fan will come on regardless of the temp?

Again thanks

[ August 04, 2003: Message edited by: RAR ]</p>

[John_D.]

You're welcome.

You did a great job with all that diagnostic work, and writing up what you did. That makes it a lot easier to help, plus it shows you know what you're doing... [img]smile.gif[/img]

Before I put a fan switch on my car, I would kick the a/c on for a minute to get the fans to come on. There are probably some parameters on it, like coolant temp above 100 degrees, or outside air above 30, or something like that. With it being summer, and with the engine warm, the fan should come on right away.

[ August 04, 2003: Message edited by: John_D. ]</p>

[RAR]

Does anyone know anything about ECM? I will try the AC trick, but if that does not work it looks like it may be the ECM - does the AT swap with the manual trans?

Also does anyone know what ECM will swap with which? and where is a good place to find one cheep - I have not tried local yards yet, but...

RAR II

[John D.]

Computer swap will have to be apples to apples. If you have auto you will need an auto PCM. Also you can't use one from a FWD vehicle, they are different.

BTW - I'm not the same John D. as above. I was here first that's why he had to put that silly underscore in his name. :D [img]tongue.gif[/img]

Edit again - I notice your from the Cincy area, where exactly? Check out the RedlineVSix board in the Regional forum.

[ August 04, 2003: Message edited by: John D. ]

[ August 04, 2003: Message edited by: John D. ]</p>

[RAR]

John - I am in Blue Ash

Does any one think it could be a blown circit on the ECM? - given what I have looked at above

Does not look like I will get a chance to try the AC trick tonight (have to work late). We will see what the result of that test are...

Again thanks to all,
RAR

[John D.]

Blue Ash isn't too far from me. I live in the Beechmont area.

To answer your question;

It could very well be the PCM that is causing the fans not to come on. You checked all the relays and they worked and you hooked up a direct power line to the fans they worked. I don't know of too many other things that would effect that.
Could it be a faulty temp sensor?

For a temporary solution you could hook up a manual fan switch like the one in the link below. I know it's not the most desirable way but it will keep you driveable and keep your car from overheating.fan switch

[RAR]

Well thanks to all that responded....

It apears to be a mis understanding on my part about these new cars....

Yes the fan will come on if you turn the AC on - even if you just start the car - they should put this test in the Hanes manual !

So here is what happened:
Basicly everything is working as expected, but to me is apears quite odd that the fan does not kick on until about 235 deg. I never let it get this hot when I was looking at it (I do NOT want to have to replace the head gaskets on this car - looks like quite a job...). So when the car got up to about 230 deg or so I shut it down thinking the fan will never come on (I was just sitting idling - so there was no air flow at all).

So basicly everything is working as expected except it apears quite odd to me that the fan does not come on until 235 deg...

In my opinion it does not apear a good idea to have the engine cycling 40 deg (from 195 to 235) before the engine will start to cool - sounds to me like this would cause a lot of thermal stress, etc... that could cause major problems in sealing

So in short does anyone know the stock fan temps on a 95 3.4L firebird? And can anything be doen about the stock setups (other then a manual switch)...

Again thanks to all,
Richard

[John D.]

Are you going by the stock gauge for the temps that you have posted?

If so, the stock gauges can be waaaaayyyyy off.

[camaro_speedemon]

Do you have a dual fan setup? If so, one is a high fan and one is a low fan. The low fan comes on with the AC and also at about 210* and I think the high fan comes on about 230* I'm not 100% sure about those temps, but I'm sure they are fairly close.

If you like to keep your car cool, do the manual fan switch that someone linked to earlier. I have the same setup and I love it. I can turn the fan on at a flick of a switch. Also the LEDs show me when the PCM turns the fans on as well.

[RAR]

Again thanks,

John - Yes I have been using the dash gages, along with a mech oil pressure gauge teed off the factory one, and a temp gauge in the radiator. The gauge in the radator (after the thermostat opens) is about the same temp as the one in the car, so I beleve it to be somewhat correct.

Also - my car only has one fan and I beleve only one speed (also it only has one relay for the fan).

I might have to consider the manual fan switch....

Thanks
RAR II