SPDEMON

Ok so, my buddy just picked up a 96 Z28 about a week ago and we cannot get the damn fans to turn on.

So far, we have replaced all 3 relays, as well as the sensor that goes in the front of the block that supposedly communicates with the Computer to transmit engine temps.

The only way we have been able to drive it was to rig up a switch that grounds the fan to turn it on. We did this by running a wire up to one of the relays, and inserting it into a female end which turns the fan on. However, it only turns the passenger side fan on.

I know that in 96' with the intro of OBD2 computers GM went from just utilizing primary and secondary fans at diff. temps to high and low speeds on both fans, thus the extra relay.

I also know that if the SES light comes on for any purpose that the fans are supposed to turn on at full speed (which they don't, we triggered the SES light on purpose to find out). As far as I know they are also supposed to come on if the A/C is turned on (which they don't).

So, unless I am mistaken, the only other thing to do is hook up the Tech II scanner and see if the computer is communicating with the temp sensor/ and fans.

I feel like I have covered most of the bases with this thing and am stumped. My buddy really doesn't want to take it to the GM dealer in fear of getting bent over - you guys know how dealers are. We are also in Hawaii and have limited resources over here. I do know a little shop that has a tech 2 that would prob. help us out, so we could prob. arrange that.

Did I miss anything? Anyone have anything to add? Is my understanding of ECM - fan function correct?

Thanks in advance, I am sure many of you have encountered this issue before.

-Matt

Zralou

iTrader: (3)

The fans don't operate on my Formy either. After checking everything like you did, I hooked up a scanner and found out the PCM was seeing 180 degrees at the point the car was boiling over.
So the PCM wasn't kicking in the fans when needed because it didn't know the car was overheating. Now the PCM won't communicate with any of the scanning software, so I have another PCM waiting to be installed.
Jumping terminal A+B on the ALDL port would turn on the fans, so I knew all the relays, wiring, fuses, etc were good.

I've just wired up a manual switch using the diagram on shbox.com, it works on a 3 way switch (center off, up high speed, down low speed). I can sit idling the car for hours now using the switch.

Sara Lou

letsrun97z

iTrader: (7)

same think here kinda just installed my slp switch and my car used to get up to 245ish sitting in traffic and the high fans never came on put the swith in and now i have high speed oh and the high never turned on with the a/c on blast seems like i done need to put the be cool thermo in now

SPDEMON

Well, I'll have my buddy try to jump terminals A+B on the ALDL and see if that turns them on.

So basically, if they turn on doing that, he is in need of a new PCM. Right?

LTSpeed

I had the same problem as the original poster and took it to a local auto electrical wiz. He found an undocumented in-line fuse blown. He also found the underside of the main board in the fuse box burned and cleaned that up. Works great now!

litch2004

iTrader: (1)

I have a 93 and mine would not work either. And you said that after 96 is when they changed to the high a low speed on the fans. Mine has a high and a low speed. iI put the same slp designed fan swith so now i can turn my fans on high or low. I can keep my temp at 160 now. Runs good. I still cant really figure out why they wont cut on like they are ment to. I did the same thing that you did, new relays and the sensor on the water pump.