Im getting the P1491 error code, however when i put the relay in, the fan runs constantly (even with the ignition off) how do i solve this problem? is it just the relay or is there something else that is causing it to run constantly?

 

i would try replacing the relay first, it could very well have failed closed. That code typically means the fan is not triggering properly when then PCM tells it to, that could mean on or off so start simple, replace the relay and go from there.

 

I've already replaced the relay, same issue, the fan is on when the key is turned to off, and the fan turns off when the key is turned to the on/run position

 

did you use a new relay? or a matching one from your PDC?

if its a known good one (works properly in a different spot) then its time to get out the multimeter and start looking for the short in the system, sounds to me like a short to ground


another question which this brings up, is the fan running forward or backward when the key is off? this will give more guidance on where to be looking for the short.

 

It's a brand new one. the fan is running forward.

 

P1491 'says open or short in the fan circuit'. Did you really think you would get lucky and have it simply be the relay? It's a 15+ year old vehicle. Get your meter out and the wiring diagrams out and start measuring things.