Ok I know its not a classic but it is an Oldsmobile. Any ways my cooling fans aren't coming on, I've had this problem before less then a month ago. I replace all 3 relays and the coolant temp switch, it worked fine once I replaced the switch. Well now my temp gauge(which runs off of a different sensor) says my car is over heating and if I pop my hood, my fans are not on. I know the fans are good, and I highly doubt that my switch is bad in less than a month. Has anybody ever had a similar problem? Thank you for your help in advance.

 

I'd start troubleshooting connectors and then components. Possibly a loose connection.

 

If I jump the relay it works so the wiring is intact. So either my gauge or sensor is lying to me or there is something wrong with my ECM or the wiring going from the temp switch to computer or from the computer to the relays. The computer grounds the relays and that is how it activates the fans which I thought was weird. I didn't imagine it using the ground to activate the relay to engage the fan.

 

Seems odd the fan operates via the computer, my '87 Olds Royale doesn't.
If you run an ignition live to the fan switch and have the relays running direct from the battery you will bypass the ecm.

I had to chastise the editor of the UK publication "Classic American" for describing H bodies as "nasty", he had the grace to publish my letter though. As I said in my letter perhaps H bodies aren't classics..... yet.

Roger.