My sons car is a 1991 Z28, 5.7 Auto. I bought the car a few months ago and it has an electrical short, when you connect the coolant temperature sensor (the sensor is located below the throttle body and is on the intake) the fan/s will not turn on. Disconnect it and the fan starts to work. The car is pretty clean and all stock. Any idea as to why?

 

Bump

 

Someone has to have an idea,,,,,, bumpidy,,,,

 

When / at what engine temp ?

When you disconnect it there is no engine temp signal to the ECM so it goes into limp home mode which puts the fan on

Have you pulled the codes to see if anything showing ?

 

As soon as I disconnect it fans work, temperature doesn't matter. The engine light doesn't turn on, but I'll try pulling codes anyway,,,,,, see what happens. Thanks

 

As I said above; is in limp home mode

You said above the fans don't run with it connected ;
at what temp DON'T they run ?

 

I'll let you know as soon as I put the car back together. I've been trying to install a set of edelbrock headers, dipstick is in the way and put a hole in the oil pan. Thanks for the help, I'll post as soon as I get it running again.

 

Sounds like the thermastatic switch (pass hd) is stuck on (grounded).
Disconnecting the temp sensor (or any sensor) should cause the CEL to come on & record the trouble code as well.Maybe the bulb is out or someone pulled it......to hide the fault!

 

Thanks for the feedback, I hope to get it running by next weekend. Also, when the temp sensor is connected, no engine light. When disconnected, the engine light comes on.