I have been trying to track down a cooling fan problem. My engine approches the 260* mark and the fans don't come on. Everything seem fine, 4.95 volts to the CTS, correct resistance from the CTS, 12.x volts to the fan switch, fuses good, new relay, ect. The fan will come on with the A/C or if I ground the fan switch. My only guess is that my dash gauge is wrong. A 10% error from it could be 20*+, or am I missing something.


Ps. What temp do the 2 other mark on the gauge indicate?

260
-- <-------------
220
-- <-------------
100

Thanks for any advice, this one has been bugging me for awhile.

 

BC,

What year is your bitchin' Camaro? Do you have a single fan, or duals?

The ECM controls the primary in a dual or the lone fan in a single setup. You can presume the ECM wiring is correct, since it is the same wiring that operates the fan relay when the AC is on. You can verify this by forcing your ECM into diagnostic mode by jumpering the terminals on the ALDL.

If that seems to be correct, and the CTS is reporting the correct resistance at a given coolant temperature, you might assume that the dash instrument is not correct. The fan should surely be on at 233°F (the third mark). The sensor for the dash gauge is located in teh left cylinder head, and should have the same resistance at temperature that all other GM temperature sensors have:

 

It is an '89 iroc, dual fans. The fan does come on when I jump the ALDL. The sender for the gauge is new, and seems to be functioning properly, but I have not checked the resistance on it.

Thanks

 

I think I see (maybe) where you've misdiagnosed it.

You have two fan relays, primary and secondary. Primary is infront of the battery, 2ndry is off to the fender side of the battery and back towards the cowl jst a bit, IIRC.

The A/C and the fanswitch in the pass side head are on the 2ndry circuit.

the ECM only controls the primary fan.

Now when you jump A and B, both fans should come on. Also, when the FS is grounded, both should come on as well.

My hunch is that the ECM is not controlling the primary fan relay, or that the primary relay is bad, or the primary fan is bad. You can swap the two relays and see if the other fan will come on.

The secondary FS should activate the cooling fan relays at 242*F (or there abouts)...since you can ground the wire and activate the fan, this might mean either the FS is bad or the temp gauge is off, since you know the wiring is intact and fine since you can ground it and make one fan work.

 

I think we may be getting closer to my problem...

When I jump the A and B, the drivers side fan comes on

Ground the fan switch and the pass side comes on

A/c and the pass side comes on


I cannot remember ever seeing both of them on. Which relay on the firewall is for the fan. (I see two of the same type up there) The one by the battery is new.

Thanks 8Mike9, between you, Vader, and the guys over at fl-thirdgen, I think I may be able to hunt the problem down. Either way, I got a bunch of stuff to check this weekend.

 

I replaced both the relays up on the firewall (I had already replaced the one by the battery.) THe fans still do the same thing, A-B makes the drivers side come on, fan switch makes the pass side come on.

It was suggested to me that maybe my 160* stat was confusing the computer, should I try and swap it out?

I haven't gotten to check the resistance on the gauge yet.

I really need some ideas here, I think I am going nuts from trying to figure this out.

Thanks,
Erik

 

I have a digital dash and the fan would not come on until it was two marks from the red.

Had the same problem. Bought a Jet 180 fan switch and 180stat. Now the right fan comes on at 200+

Put the Jet parts in and now all the worries are gone...

 

Did you check the fan switch itself? Remember there are 3 different coolant temp. sensors in the engine: one for the computer (CTS), one for the dash, and one for the fans ie fan switch (the fans don't operate off the computer's CTS). If you can ground out the wire going to the fan switch and get the fans to come on, and the CTS checks out (this doesn't control the fans anyway.......), the only thing left realistically is the fan switch sensor itself.

Just my .02

 

On my GTA the left is controled by ECM. YOu can hook a scan tool and watch it request it. The right fan is controled by the head pressure of the a/c and the fan switch between the last two plugs on the right side. I think the right one is the fail safe. Anyways if you replace the right one with a 200 on switch the right fan will come on at 200deg...