Questions and Answers
Sundance Cooling Fan - Revisited
Q. Vincent, I recently requested your help on my 1994 Sundance, 2.5, A/C, P/S, approximately 133,000 miles. The cooling fan will not turn on at the appropriate time. The entire cooling system is new. After performing the techniques you suggested, I determined that the engine control computer was at fault.
I replaced the computer with an A-1 Cardone rebuilt unit and now the fan does come on, but only when the temperature is almost at the danger zone, 260 degrees! I suspect the computer is defective.
I think the circuit board has resistance which is way too high because the resistance of the coolant temperature sensor reads 500 ohms when the fan finally goes on. According to the specification, the coolant temperature sensor should read 700 to 900 ohms when it activates the computer which in turn grounds pin 31. The only item I have not replaced is the relay. But I don't think a defective relay would function when pin 31, (blue, pink) is grounded and I don't think its coil resistance is related to the temperature sensor circuit.
I have checked the resistance of all wiring going from the coolant temperature sensor to the computer and they are all zero ohms. How can I test the resistance of the fan circuit of the computer to determine if the computer is defective? I am being driven mad by a lousy Chrysler product.
Please help!!!!
FrankA. There are no specifications for the PCM as far as the internal workings go so we can't tell if the PCM is god or not. The fact that it does turn the fan on shows that it is working. There is a 5 volt reference voltage that goes to the sensor. I would make sure that reference voltage is there and is indeed 5 volts.
To keep sensor readings accurate at all times, the PCM routes the reference voltage through either a 10,000 ohm resistor (cold operation), or a 909 ohm resistor (warm operation). The resistance circuits are inside the PCM and I don't know how you would check them.
Maybe if you put a 250 ohm resistor in the circuit and see if the fan kicks on at the right temperature...
Additional Information provided courtesy of ALLDATA
