Aftermarket October 2022

BY Kevin Toms T he subject this month is something I am sure we have all come across; Parts that cause more problems than they solve. The vehicle in question was a 2006 Chrysler 300C with EDC 16CP31. This car drove in to us under its own steam with a constellation of lights shining in the dash, including the battery warning light. As usual, we started with a global scan of the vehicle while on battery support. Upon completion we found several low voltage fault codes, but the one I was most interested in was U1132 Lost Communication with Generator – Active. Armed with this information I formulated a test plan: 1) Test the vehicle battery 2) Check voltage at the battery to see if it was charging at all with the engine running; The answer was yes, and we could use an amp clamp as well but I saw no need 3) Find a wiring diagram for the system so we know what should be where and connected to what, I.E Comms line 4) Find the alternator on the vehicle physically to do testing 5) Do volt drop testing on ground and B+ side as we need both of these for the alternator and comms to work correctly 6) Connect the scope so we can see what is happening on the LIN bus control wire 7) Make a decision on the fault according to outcomes. 28 AFTERMARKET OCTOBER 2022 TECHNICAL www.aftermarketonline.net BUILDING IN A FAULT A recent job involving a Chrysler 300C gave Kevin the opportunity to discuss replacement parts that cause more problems than they solve Upon testing the vehicle battery, the result was; ‘good - needs charging’. This was only to be expected, so a substitute battery was put in and the original put on charge. It is always best to start with a known good and we already had a copy of the DTCs that were present. With the multi meter installed across the battery and 12.6v shown, the car was started up and the lights turned on to load the system. The voltage was going down even when picking the revs up. This proved why the battery light was on in the dash and why we had the alternator LIN bus malfunction DTC. Next, I found the alternator, which was on the driver's side under the engine. To get at it, I had to go through the suspension and subframe. As I had the scope at the ready, I first checked between battery ground and the alternator casing. This showed less than 100mV, so good. The next check was between battery positive and the B+ terminal at the rear of the alternator. Again, the same result here, less than a 100mV. This was good, both passed. For the next test, I connected the scope using a back probe in to the Lin bus connector. I found a good signal, 12 volts to about 0.5 of a volt, so it passed that test. Please refer to Fig.1. Wiring and response integrity At this point we knew the LIN bus signal came from the engine control unit ECU, so we didn’t need to test there as the signal was good. It was looking like the alternator is