So I have a completely stock 1997 XJ with the 4.0 that was laid up since July with a bad PCM. After installing a new one that was programmed to my jeep, it starts and runs fine, but spits out a p1491 (rad fan control relay circuit) code. The fan comes on when the key is turned to the on position and runs the entire time the engine is running. I've swapped relays and checked fuses and it's still showing the code and the fan is still misbehaving. I know it's not a bad problem to have, but I can't pass inspection next month with a check engine light.
The coolant temp sensor is good and reads accurately, the air conditioning is off, so what else controls this fan?

 

The ac high pressure switch is a dual circuit switch if it senses high pressure in the freon it will open one circuit to kill the ac compressor clutch...the other half will close to turn on the fan but I don't think that throws on any codes .was your pcm "new" or used rebuilt .

 

Have you gotten any closer to solving this issue. I’m having the same problem and am at a loss for resolution

 

I would start by checking at the relay socket. If the relay is good and the correct one, then I'd suspect the wire from the relay back to the PCM is shorted to ground. Or the driver in the PCM is bad and shorted through to ground. The diagram for a 1997 is below, with that wire highlighted in red. That's connector 3, pin #2 on the PCM.