A call came in last week on a 2001 Dodge Durango with a 4.7L engine and a 44RE transmission. The only information given by the technician stated that the indicator light was flashing from right to left. My first thought was -- why would a technician call ATSG for a turn signal problem when we are automatic transmission specialists?

I returned the call and found out that the problem was in the shift indicator. The tech also stated that the scanner showed a “Code P1698 - Loss of TCM to PCM communication.” My first thought was to have the tech check and see if the correct VIN number was programmed in both the Power Control Module (PCM) and the Transmission Control Module (TCM). After verifying that the VIN was correct, I suggested that the tech start checking communication wires between those two modules. I emailed the wiring diagram and the connector views for the communication lines because, as many of us know and have been there before, a communication code is not always the easiest thing to find and fix. The location of the modules can be difficult to find and even to see the connections clearly once they are located. So after the tech checked the communication wiring between the TCM and the PCM, he called back and let me know that he had no connection from the PCM pin 30 to the TCM pin 43. So, now what should we do for the next step? We could send the whole job down the road to the electrical shop and lose the revenue that it could bring in, or we could take a closer look at what the possible cause could be.

In looking at the wiring diagram (Fig. 1), you can see that the violet/yellow (vio/yel) wires are not connected directly to the PCM and the TCM. Rather, there is a diagnostic port junction in between the two modules that also feeds all the modules. Once it was determined that the vio/yel wire from the PCM pin 30 to the TCM pin 43 was where the problem was, I had the tech apply 12v to pin 2 in the ALDL connector (note do this only with the TCM and PCM disconnected to protect the components) and then load test the circuit with a headlight at both the PCM pin 30 and TCM pin 43. What he found was that the headlight lit up brightly on the PCM pin 30 but did not light up on the TCM pin 43 at all. What was our next step?  

COMPUTER DATA LINES (Fig. 1)

ATSG COMPUTER DATA LINES (Fig. 1)

 

 

It was time to locate the diagnostic junction port hidden under the left side of the dash. I explained that this diagnostic junction port is also called a shorting bar in some vehicles and is most likely a white connector with all the wires coming and going being vio/yel in color. After some time the tech called back and stated that he had found the problem!  He had found (as usual in our line of work) someone else had been there before him. He found that two of the wires had been pulled out!  We know that one of them went to the TCM. Most likely the second wire went to the instrument cluster. After reattaching the wires, the problem was immediately solved. No more P1698 Code and the malfunctioning shift indicatorlight that was flashing from right to left turned into a properly‑operating shift indicator light that settled on the actual gear you selected.


TRANSMISSION WIRING (PART 1)

ATSG TRANSMISSION WIRING (PART 1)


 TRANSMISSION WIRING (PART 2)

ATSG TRANSMISSION WIRING (PART 2)

 

I know that when a communication problem arises, panic sets in. We don’t know where to turn but, armed with a few wiring diagrams and some test equipment, we have the road map to tell us not only where to go but how to get there.

This article write up was provided by one of our knowledgeable techs, Rick Sons. 

If you found this article to be helpful, let us know below. If you need technical help from one of our tech experts, give us a call at 1-800-245-7722 and we will be more than happy to assist in getting that job done and the customer out the door!

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