Chrysler Repair: 97 Concorde - cooling fans dont come on, coolant temp, variable resistance

Question
My engine is overheating at idle because the cooling fans don't come on. On the road at a decent speed temp stays OK even using a/c, so water pump and thermostat seem OK. The odd part is that when I start the car COLD and turn the a/c on the fans come on with the compressor as I understand they should. However, after the engine reaches operating temp the fans don't come on, either with or without the a/c on. I've bled the cooling system, swapped high and low fan relays in the PCM, and checked fuses. I have the factory manual, but have run out of options...or have I?

Answer
Hi Ted,
It appears to me that the coolant temp signal is not getting through to the computer or the sensor is inaccurate. It is located next to the thermostat housing and has a tan/black wire and a black/light blue wire. The former is attached to pin 2 of the pcm and the latter is attached to pin 4. The sensor should read a variable resistance across those two contact when you remove the plug and measure it. When cold it should read 7,000 to 13,000 ohms and when the engine is warmed up it should read 700 to 1,000 ohms. So check that and also the continuity of the wires from the plug to the pcm pins.
You also could try a fault code readout using the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains on, to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to be sure of getting an accurate set of flash counts. Group the counts in pairs in the order of appearance to determing fault codes. The last code should be 55 which means end of readout. A 17 code says the computer sees the situation that it appears the coolant is too slow in warming up, and the 22 code says there is a voltage signal that is outside the expected range  and would suggest a problem with the signal wire being shorted to ground or shorted to a voltage carrying wire. '97 was a transition year so if you don't get flashing at all you will need to get a readout via a plug-in reader using the socket under the dash by the steering column. Autozone parts stores will often give a reading for free.
Let me know what you find.
Roland
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