This article will document the U0100 code – Lost Communication with ECM/PCM; a code that involves a no-communication issue with the powertrain control module. In the world of automotive module-to-module communication, it can mimic a good guy/bad guy situation. The good guy has made an attempt to communicate with the bad guy and the bad guy does not respond. The good guy will then report to whoever will listen via a U-code that the bad guy is not talking. So keep in mind that the module storing the U-code is, in many cases, the good guy.
Our diagnostic journey begins with a 2010 Dodge Caravan. The vehicle has been taken in for an emissions test and has failed to communicate with the state’s equipment. This failure-to-communicate issue is not by any means unique. What is unique is this vehicle has a signature to it in terms of what it does when it attempts to communicate: the wipers will sweep once across the windshield and the headlamps will illuminate once and then turn off. (This is the situation that was reported in a previous article on the art of talking, August/September 2014.)
This vehicle was scanned by several generic scan tools as well as the manufacturer’s scan tool. We were able to obtain scan data with both types of tools, but you must keep in mind that in order to pass the emissions test, you must pass on the state’s equipment. I will attempt with the following pictorials to outline the series of events as they unfolded.
The first pictorial (Figure 1) shows a breakout box being used to scope the communication lines.
The vehicle was scanned first with a Chrysler scan tool and the following activity was noted: the wipers performed a sweep across the windshield. The next pictorial (Figure 2) shows that with the Chrysler scan tool we were able to obtain good information concerning the health of the vehicle. The vehicle was able to communicate and we could see that all monitors had ran and passed.
The communication architecture of this vehicle is quite interesting. There is a central gateway called the TIPM (totally integrated power module). The scan tool must first go through the TIPM in order to speak to the PCM as well as other modules (ABS, ORC, WCM, etc.), which reside on what is called CAN C. A series of other modules (CCN, HVAC, radio etc.) are also on what is called the CAN IHS line. The topology screen above (Figure 3) shows a layout of the modules for this vehicle. A generic scan tool was used to take a second look at this vehicle. Figure 3 also shows the information on this vehicle, which now shows codes are present.
The codes were then reviewed and the system showed we had a series of U-codes in the system. The diagram above (Figure 4) denotes these codes.
It appears that the WCM (wireless control module) is the one setting the codes that we have the most interest in. The two codes are U0100 (ECM Not Talking) and U0001 (CAN C Issue). This information implies that there may be a communication issue with the CAN C line causing us not to be able to communicate with the PCM.
It is now time to use our Pico Scope to determine where the fault may be hiding. The following pictorials (Figures 5 and 6) show what was witnessed on this vehicle. The CAN C and CAN IHS lines appear to be fine.
It is interesting to note that the DLC should be checked from time to time. It has become important over the years to verify that the DLC has the proper wires in their terminals. There have been a few cases where the wiring diagram did not match what was shown in the schematic. Figure 7 shows what was shown per manufacturer information vs. aftermarket.
The manufacturer’s information shows that per the DLC, there are five wires. When I looked at the actual number of wires at the DLC on the vehicle, there were 10 wires noted. A review of the aftermarket wiring diagram showed that 10 wires should be at the DLC, see Figure 8.
This 10-wire DLC has two wires that were in the wrong terminals, I simply opened the DLC connector, backed out the two wires and placed them in the proper terminals. The vehicle then passed the emission test with no issue. It was an issue of the DLC not being properly wired. In closing, keep in mind that there is a five-wire design as well. The only vehicles that exhibit this strange behavior are ones with the 10-wire DLC.
This Pulling Codes case is now solved.
