'05 town and country: multiple electrical gremlin

QuestionEdit

QUESTION: Roland, I'm asking for feedback on an electrical problem I consulted you on in January. I have the 05 T/C with the radio, wipers, both blowers, power windows, headlights and horn not functioning and the seatbelt alarm won't go off when belt is on. I took the van to a dealership today and they said that half of the TIPM doesn't power up, and that when they jumpered power to it everything worked. I am skeptical of this because Rob, the other person with the same problem, stated that he had changed it in his and it didn't help. I brought the van home without letting them change it and I checked the voltage at all the fuses and they all checked out ok. Could they be right or are they trying the make money ($500.00) off me? I asked the service tech how he was able to jumper the TIPM to get it to power up and all he said was "don't try it" and offered no further information. Sounds a little fishy to me.

ANSWER: Hi Pappy, That does sound fishy. I would not buy into a new IPM. It appears to me that all the failed circuits that you listed rely upon their getting activated via the front control module (FCM) which is the small electronic computer part at the very front end of the IPM and which has a 49-pin plug that plugs in directly to the IPM box. The failed circuits each have their own 'driver' pin of the FCM that activate it. However, the FCM itself does need 12V to power it that arrives on pins 1,2,9,and 38 directly from the battery via the IPM. Also the FCM needs to get digital messages via pin 22 of the 49-pin plug. I would release and rotate the IPM to give you access to the FCM. Then remove the two screws that hold it to the IPM. Then pull the FCM straight out of the IPM and verify that you show 12V on those 4 pins of its socket. Let me know what you find. My suspicion, if the FCM is getting that power, would be that the FCM is bad. You might also try a spray can electical contact cleaner to clean the 49-pin socket and pins I listed of the FCM that go into it. Roland

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QUESTION: Roland, Pin #38 of the fcm receptical is dead. Also pin #1 in the receptical has a resistance value of 35 when I ohm it out with the positive power plug witch is much higher than pin #9 (3 ohms). Pins 2 and 38 won't ohm out with the 10 plugs removed but 2 ohms out a 3 ohms with the plugs in and 38 won't ohm out at all. Is there a way to open the IPM to possibly repair or resoder the bad connection?

ANSWER: Hi Pappy, Let me revise my previous answer. The pins 1,2, and 9 of the 'fcm receptical' (by that you mean the socket on the front of the box, correct?) should show 12v. Is that correct that they do? What is "positive power plug" or do you mean "socket" (where is it located, what color wire, where does it come from?)? I can't make any sense of the ohm readings WITHOUT a better understanding of what you are measuring. Maybe you mean that a large red wire from the battery goes to a 4-pin black plug on the back of the IPM and that is supposed to provide the power that you should find on 1,2,9 of the FCM socket. Does it? Pin 38 is also supposed to show 12v "when the 4-pin plug is not engaged", does it? I am not clear how that comes about but that is what the diagram says. So rather than worry about the resistance values, tell me about the voltages. I am not certain there is anything wrong inside the ipm, yet. Roland

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QUESTION: Roland, Pins 1,2, and 9 of the fcm receptical on the front of the box all have 12 volts with all plugs engaged. I cant get any voltage in pin 38 with the 4-pin plug from the battery not engaged, nor when it is engaged. You are correct, I was checking continuity between the 4-pin positive receptical that the plug from the batery plugs into and the pins in the receptical for the fcm. Thanks for yor time and effort. Pappy

AnswerEdit

Hi Pappy, It may be that socket pin 38 is not like 1,2, and 9 in being dependent upon the 4-pin battery input line but rather when the battery input is disconnected that somehow it gets 12v from one of the other circuits that are connected when the FCM is plugged into the IPM. I am not certain why this is set up that way but that is what the diagrams say, cryptically. Maybe you can sneak a wire wrapped around pin 38, then plug the FCM in so that you can actually read whether 38 shows 12V when it is plugged in (measure both with and without the main 4-pin battery plugged in to the IPM). Because you do show 1,2, and 9 to be powered up, that does hint at the problem residing inside the FCM. In theory there could be 12v brought to the pin 38 situation even with battery plug removed because there is another battery wire beginning at the battery clamp that goes to pin 9 of the blue plug on the back side of the IPM. By the way, that wire is involved in the hazard flashing light circuit and because it is a fine wire it may have been corroded and 'opened' at the clamp. So examine for that possibility which I note that has happened to other minivan owners. You might want to verify that FCM pin sockets 8 and 43 show 0 ohms to ground as those are for the purpose of grounding what is going on in the FCM. My inclination is that no matter what you learn about pin 38 it is likely not the cause of your non-functioning circuits. Rather I would suspect the FCM itself as the cause because exactly the things that aren't working are the responsibility of the FCM. How much does it cost? I wonder about the dealer mechanic saying that half the TIPM was missing. Do you see any sign of that? Where did the they jump to? There are some fuses that get 12V all the time, and some that only show 12v in the 'run' position, and some when in the run position and when you have asked for that circuit, so we'd have to sort that out. But it would be interesting to know where they "jumped" 12V to. Maybe they just circumvented the FCM with their jumper, which of course could explain how they got 'everything' to work. But maybe not. So do see if you can talk to the same person again on that subject. Roland PS Thanks for the rating and nomination. By the way, you are entitled to rate and nominate with each new answer I give, if you are so-inclined. Thanks for the second rating.

PPS: Here is what the FCM controls: accessory relay, brake transmission shift interlock, rear window defogger, front and rear blower motor relays, fog lamp relay, windshield washer, windshield wipers, headlamp power and voltage, horn relay, radio speaker relay, park lamp relaly. This certainly seems to be many of the items you notice aren't working.

PPPS: You would also do well to verify that the wire that carries the digital data to the FCM is patent. It runs from pin 22 at the FCM socket to pin 9 at the diagnostic data link socket under the dash by the steering column (where you plug in a code reader). If that were 'open' that would explain the non-function as well.