Chrysler Repair: fan turning on at start up, then turn off, coolant temp, roland roland

Question
93 intrepid, car starts, and fans kick in to high as it seems, they stay on for a while then, they shut off. I put my fingers on the fan relays high and low, to see if they click, and they do, is this a problem with the fan motor going into low? also once they stop, they wont go back on, but will start up everytime the car is started, codes i got were 12 and 35

Answer
Hi Carlos,
The 35 code basically agrees that there is a problem with the fan relay control circuit(s). It could be the coolant temp sensor is faulty, or the wires from it to the PCM are damaged, or the wires from the PCM to the relays are faulty, or possibly the relays are sticking closed. Check the resistance across the pins of the coolant temp sensor after removing its plug. When the engine is cold it should read 7-14,000 ohms and when the engine is hot it should read 700-1,000 ohms. It is located near the thermostat housing on the top front of the engine, where the top radiator hose is attached. Its wire colors are black/light blue and tan/black.
You could try switching the relays; and also testing whether the contacts are closed when they are not installed (measure across from pin B to pin D), and you should find them to have no connection. Other than that it is a matter of checking the wiring from the relays to the engine controller. It could be the controller itself but that would be the last choice after eliminating all other explanations. Let me know if you want more detailed tests to do with a volt-ohmmeter.
The 12 code means the battery supply to the controller was disconnected sometime in the past 50-100 key cycles. If that is not the case then check the battery clamp/post interfaces and the wires to the controller.
You might try shaking the harnesses when you first start the car to see if you can induce the fans to stop. Of course, recall that the fans will always come on when you have asked for A/C.
Roland
Roland