when I jumper the diagnostic port as if I were going to run codes, only the driver's side fan comes on. The fan on the passenger side never comes on, even when the coolant temperature reaches 240 degrees. I want to check the relay, but I don't know it's location (there are a lot of them). Is there something else it could be (besides the fan motor)? Where can I find a wiring diagram of the twin-fan circuit? thanks!

 

Passenger side comes on only when the A/C is operated.

 

hmmm...I'm pretty sure they both used to run when I shorted the diagnostic port. could be wrong, I guess. I'll check to see if they come on when I switch on the A/C. thanks!

jb

 

On my 88 they both run with the AC, driver's side runs on diagnostic and mid temp from ECM, passenger side runs from high temp on it's dedicated sensor, passenger side head next to exhaust down pipe. Whole bank of relays just above the master cylinder.

 

Look in lower right corner of this diagram: