Cooling fans not coming on: '01 t&c

Last Edited By Krjb Donovan
Last Updated: Mar 11, 2014 07:47 PM GMT

Question

QUESTION: Hi there wondering if you can help. I have a 2001 Chrysler T&C the rad fans are not coming on. I found the fan relay jumped the wires and the fans work but no matter what I do they do not come on. I only have power on pin 1 all the rest are to ground, can you please tell me what should be happening at each wire when the motor gets to temp or how to check to see that the pcm has not shorted to ground on the input to the relay.

Thank You Steph

ANSWER: Hi Steph, Pin 1 has the 12v from fuse 27 that would power the fans if the relay closed and that would be seen on pin 2 (dark blue/dark green) when the relay closes. The pin 3 black/dark green is the ground wire for the relay activation coil. The relay is activated when/if the pcm puts 12v on pin 4 dark blue/violet wire and that should happen when the pcm gets a signal from the coolant temp sensor that is has reached about 200F. The first thing to do would be to check the coolant temp sensor to see if its resistance drops from 4,000 ohms down to under 1,000 ohms when the cooland goes from cold to near/about 200F. It is located next to the thermostat housing (violet/orange, dark blue/dark green wires). It may be that sensor is faulty. Then if that looks ok see if 12v appears on the pin 4 wire(put a straight pin through the insulation to make contact with the internal conductor) when the temp gauge is moving toward 3/4 scale. If it does, then the relay is bad, if it doesn't then we have to check that the signal wire from the sensor to the pcm is patent and that the wire from the pcm to the relay is patent. The other thing to do would be to get a fault code readout using the ignition switch:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window to see the mileage reading replaced by a 4-digit number which is a code that might tell us exaxtly where the fans circuit is failing. Let me know and we'll go from there. I suspect the relay has gone bad, but let us see what you learn before replacing that. Roland PS Please 'rate' my answer. Thanks

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QUESTION: Sorry that was 0.32v at pin 4 on relay harness at all times no change

ANSWER: Hi Steph, Check it with the plug pulled and when the gauge shows 3/4 scale. If the relay is bad it could 'pull down' the reading on the wire when it is attached. If it still shows only 0.32v then verify the connection between the pin 4 and pin 73 of the pcm. Also if the connection is good, try reading the voltage at pin 18 of the Natural shell/Red internal pin socket of the integrated power module as that is where the wire from pin 73 of the pcm connects to, and from there exits the ipm on pin 1 of the Green shell/Blue interior plug of the ipm to go on to the relay pin 4. That is the full circuit to actuate the relay. Roland

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QUESTION: relay removed still 0.32v pcm pin 73: .91v when motor running- 12v not running but key on...don't think this is the correct pin pin 4 and pin 73 of the pcm: 0.55v-ohms not getting reading voltage at Natural shell/Red pin 18: 0.31v Green shell/Blue interior plug pin 1: 12v

Answer

Hi Steph, The voltage readings that I gave are based upon the engine being hot enough that it is asking for the fans to be 'ON' (3/4 scale on the temp gauge if that is accurate). So that might explain why your readings are sometimes low, sometime high if the temp was at the edge of the point where the fans are supposed to on or off. Pin 73 is the fan relay control pin and has a brown/violet wire on the plug of the pcm Where you say "pin 4 and pin 73 of the pcm: 0.55v-ohms not getting reading": do you mean 0 ohms or infinite ohms? It should be 0 ohms which shows they are connected. The readings at the ipm are not important (and will be confusing unless taken with the plugs inserted and the wires probed with a pin) if you have shown there to be 0 ohms between pin 73 of pcm plug and pin 4 at relay plug (i.e. that they are connected together). The voltage that has to be present for the fans to run is 12V at pin 4 of the relay plug and it should be there when the temp is high enough that the fans are needed. If you have that and you don't get fans, then the relay is bad. If you don't get 12V on pin 4 wire then you have a wiring/pcm problem. AGAIN: This assumes the engine is HOT. Any chance you might rate my answers? Roland

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