1992 Pontiac Bonneville cooling fan issue

[scottch]

Ok, just want to make sure I understand correctly how my cooling fans are supposed to engage. From digging around on this forum, from what I gather, the temp sensor located on the back of the manifold sends the coolant temperature to the ECM. Once the temp reaches 200 degrees the ECM sends a signal through the low speed fan relay switch to turn the fan/fans on at low speed. Once the temp reaches 225 degrees the ECM sends a signal through the high speed fan relay switch to turn the fans on at high speed. My fans weren't coming on at all other than when I turned on the air conditioner. I replaced the temp sensor on the back of the manifold and now the fans will kick on at 225 degrees, but they don't turn on at 200. I tried switching the relays and I still see the same thing. Would this lead me to believe that there is an issue with the wiring path of the low speed relay switch? Thanks in advance for any help.


Scott

[rustler85]

i would say shoot the wires from high speed and low speed cause if i remember correctly those two are related when it comes to certain wires from both .. do a continuity test on them with a multi meter... doing that your only looking for a tone...

[96 SSEi]

hi, the coolant temp sender is located directly below the thermostat housing where the upper rad hose meets the block - on my 96, it was 3 wire. this is on the front of the block and not on the manifold as you stated in your post. If high speed works but not low, and you have checked fuses and relays properly, I would suspect the PCM is not commanding low cool at the specified temp - I had this issue on my 96 which led me to install a thermostatic resister to trigger the fans at 90c. my 96 had over 300,000 and didnt want to swap pcms

is it possible for you to swap a known working pcm to diagnose the issue?

[RJolly87]

Low speed fans come on around 215*. You are correct however, they should switch to high at 225*. I would scan live data to confirm temp readings and whether or not the computer is commanding fans on.