Powertrain Control Module (PCM) and radiator fans
Problematic1963
05-07-2007, 09:26 PM
I have a Caravan 1997, 3.0, with a 3 speed transmission, 121K miles. A few day ago, I turned on the AC and noticed that it was blowing warm air. Looking in the engine compartment I noticed that the compressor was extremely hot and realized that the radiator fans were not working. I took a water hose and hosed down the radiator and immediately cold air started to come out of the vents, indicating that the compressor is still ok.
I checked the cooling fan fuse and it was ok. I disconnected one of the 2 fans and jumpered it to battery and the fan ran normally. Searching this forum I found numerous posts about defective electronic relays and went to Autozone and bought a replacement. It didn't help. Finally, armed with my Chilton Repair Manual, I looked at the electrical schematic to try to further diagnose the problem. I disconnected the battery and then disconnected both 40 pin connectors going to the Powertrain Control Module. The cooling fan relay control output on the PCM of this car is on pin #73. So I reconnected the battery, with the PCM completely disconnected and shorted pin#73 on the connector (not on the PCM itself!) to ground. The fans immediately started running. Disconnecting ground from pin#73 would immediately turn-off the fan. It confirmed that the fan and relay are ok. Just for the sake of it, I reinstalled the old relay and it didn't work confirming that the old relay was broken. But, from this, it appears that something may be wrong with the PCM. I figured that the PCM gets the proper information that the AC is turned on, as it still properly controls the A/C compressor clutch. It looks like the cooling fan relay output of the PCM is dead. :banghead:
Where do I go from here? Could the PCM have a diagnostic code preventing the proper operation of the cooling fan (I don't have access to a code reader) Any idea for other things I could do or try?
Thanks!
I checked the cooling fan fuse and it was ok. I disconnected one of the 2 fans and jumpered it to battery and the fan ran normally. Searching this forum I found numerous posts about defective electronic relays and went to Autozone and bought a replacement. It didn't help. Finally, armed with my Chilton Repair Manual, I looked at the electrical schematic to try to further diagnose the problem. I disconnected the battery and then disconnected both 40 pin connectors going to the Powertrain Control Module. The cooling fan relay control output on the PCM of this car is on pin #73. So I reconnected the battery, with the PCM completely disconnected and shorted pin#73 on the connector (not on the PCM itself!) to ground. The fans immediately started running. Disconnecting ground from pin#73 would immediately turn-off the fan. It confirmed that the fan and relay are ok. Just for the sake of it, I reinstalled the old relay and it didn't work confirming that the old relay was broken. But, from this, it appears that something may be wrong with the PCM. I figured that the PCM gets the proper information that the AC is turned on, as it still properly controls the A/C compressor clutch. It looks like the cooling fan relay output of the PCM is dead. :banghead:
Where do I go from here? Could the PCM have a diagnostic code preventing the proper operation of the cooling fan (I don't have access to a code reader) Any idea for other things I could do or try?
Thanks!
Problematic1963
05-09-2007, 08:51 PM
I brought the car to the local Dodge dealership for diagnostics and explained what I had done. They called me later telling that everything is working fine but they didn't find any problem. Their explanation is that this was probably caused by a bad contact and was fixed after they cleaned them.
I hope this is true and that it does not quit again in a couple of days
I hope this is true and that it does not quit again in a couple of days
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