Car is a 92 RS with the 305 tbi. It has the single fan setup. The fan does not turn on when it is in diagnostic modee checking for codes. The fan does work while the AC is engaged. What could the problem be?

 

Are you getting power to the fan?

 

I believe I am getting power to the fan since it turns on when I turn the ac on.

 

Check to see if it's sending power to the fan when it's supposed to be on.

 

My wiring diagrams for the 92RS with TBI do not show the fan being PCM controlled. Therefore, don't expect the fan to come on when in diagnostic mode. The fan is controlled by the fan relay which is activated 3 differen ways.

First the relay is activated by the HVAC control switch. The fact that your fan runs when AC is on tells us that the relay and fan are okay. Second, it is activated by a temperature switch located in the pass side cyl head, below and between 6&8 spark plugs. There is a green and white wire going to it. Grounding this wire with the key on should turn on the fan. If not, check and repair the wire. If the fan comes on with this wire grounded but does not come on when the engine is hot, replace the temp switch.

Third, the relay is activated by the AC pressure switch(on 1991 or early production 92). This would be redundant to the AC control switch and not important since the fan runs whenever AC is on.