Thread: Cooling Fans Not Turning ON

We just totally rebuilt our L67 with the addition of a mild cam and headers. I'm showing a random misfire code which I know is the result of the cam. I'm going to get the car tuned in a week or so and have that code removed. The car is running great so far after about 400 easy miles. The problem I have had since the first start on the new motor is that the cooling fans won't come on unless you turn on the AC. My friend changed the PCM to have low speed fans come on at 186 and high speed at 190. The inside gauge is showing 210 and the fans don't come on. I turn the AC on and the fan comes on and the motor cools down. I replaced the coolant temp sensor with the build and thought maybe it was bad. I just replaced it with a new AC Delco one and am having the same issue.... The guy at AutoZone mentioned it may be a relay. Any similar experience with anybody? Thanks for experienced advise

I just read a post from a few years ago on here http://www.grandprixforums.net/my-97...ved-38893.html This is exactly my symptoms. I unplugged the sensor wiring harness and the fans run in high speed. Is it possible that the second Duralast sensor is bad also??? The harness seems to be clean and intact on both ends... The fans worked perfectly before I pulled the engine but like I said I replaced the sensor with a new one. If your wondering why its because I bumped it with a wrench and broke it

the more I read about this I think its another bad sensor. I'm going to try another brand tomorrow.

Have you swapped relay's around to see if that makes any difference?

Actually they both are Duralast sensors from Autozone not AC Delco.... don't know why I wrote that??? I haven't tried switching the relays yet but both fans will work. if I unplug the sensor both fans spin on high speed. If I turn on AC both fans spin on low speed.

I've been going through ECTs like toilet paper too, mine are BWD though. There are actually 2 sensors in there, one for the PCM and one for the gauge itself. Mine has always had problems on the gauge side of things.

Bought a Borg Warner sensor from orileys and still having the same problem. Guess I'll have to get this thing diagnosed on a computer scanner and see wtf is going on

Try swapping relays around

Ok finally think I've got this issue figured out. The programmed cooling fan changes my buddy made didn't take the upload. It looks like the factory settings are still there and the fans do turn on at 215. I think my old temp sensor just registered a little lower in the car. The scanner showed nothing wrong with the relays and the temp reading just about the same as the gauge in the car and the fans did actually come on. I think I just didn't let it get hot enough for the factory settings to kick the fans on. Guess my old sensor just made my gauge register lower. Or maybe the modded motor runs a tad hotter? Anyway tomorrow I'll have my friend hook up his laptop again and adjust the fans to come on at 186 and 190 again. Hopefully my pcm will take the change this time....

My friend uploaded the cooling fan changes again today and this time it took. The low speed fans kick on at 186 and the high speed kicks on at 190. This change keeps the temps a lot cooler when stopped in traffic. Seems like my 180 thermostat is more like a 185 tho...??? Think I'll try another one and see if the cars stays a little cooler