Chasing Ghosts

Not so sure how this might ever apply to anyone else, or another coach, but I have been chasing a ghost, which has finally disappeared! We spent 3 months “work camping” at a national wildlife refuge, which is a whole other story about that, but we’ll save that for another time. Mostly due to not being able to easily drive in or out of the camp site, we didn’t move the RV for almost 3 months, just before we were going to leave.

When I fired the machine up, I immediately got warnings from the transmission and both the ABS and Traction Control warning lights came on. We were already committed to a camping trip (ironic term when you live full time in an RV) with family and didn’t have a lot of time to trouble shoot this. I confirmed that the transmission would still work as would the brakes. The warnings came from a failure of the main computer data bus that sends data around between the engine, the brakes, the transmission and maybe some other things as well. The tranny will not give optimum performance since it can’t talk to the engine and the ABS system won’t be active but the normal brakes still work. So we continued on for the camping trip.

Soon after that, we moved to a conventional campground and I did some basic trouble shooting but couldn’t find anything of note. Then I had a 1000 mile trip from Texas to Indiana and things changed a bit. Usually the transmission was OK with the data but the ABS system usually wasn’t, although the light would flicker off occasionally. Once in Indiana, I did some checking with a data analyzer that was supposed to read the data bus, but didn’t show anything useful. IN fact, it generally couldn’t read anything on the bus.

Next, I looked at the data lines with an oscilloscope and probed around some more. The data lines were definitely not looking right, but I couldn’t identify any specific causes. After sitting a couple of weeks, we pulled the coach out to have some work done. We had to drive it about 10 miles, and there were now serious warning bells going off constantly. Nothing like that had happened on the 1000 mile drive, but you could barely stand to be in the cab with all of the noise. The dogs who were with us were not happy with the racket. It turned out that the repair facility wasn’t prepared to do the work (even though it had been a confirmed appointment with them), so we brought it back and parked it again.

Now I had to get something done, so I probed the data bus through a connector right beside the engine that I had been working on before the trip with all of the racket. That time I noted that it was not properly constrained by any kind of mounting but just left to flop around on the end of about 9 inches of wire. I had temporarily secured it with a tie wrap then. I was convinced that this wasn’t a coincidence so I thought that there had to be a problem caused by the poor installation that I had made worse by moving it around.

I tried to find a repair shop that new more about diesel power systems data than I did, but didn’t have much luck here in Indianapolis. The local Freightliner dealer (by reputation one of the better shops for this kind of problem) wouldn’t even look at it since a) it wasn’t a Freightliner chassis and b) it was over 7 years old. The closest place I could find to take it was Columbus OH, which wasn’t appealing. The local Cummins dealer offered to run their diagnostic equipment on the data and give my any results they got, but would only work on it if it were an engine fault code. They would do this at no charge, which I really appreciated.

I went back to that connector again and did some more testing on the bus to see if I could find anything, removing the cable tie I had added and generally probing the cable and connector, but didn’t find anything. We drove the vehicle to Cummins (about 10 miles) with nary a peep or warning light coming on. A MIRACLE. They found one error code which the technician told me he had seen 2 or 3 times recently, but it wasn’t a Cummins code and their factory guys had no idea what it was, but it looked like a proprietary code instead of one of the SAE standard codes. We drove back without any additional fault lights coming on so it was definitely better. Maybe even fixed somehow.

Now I was convinced that crazy connector and its cable had to be the culprit! Next, I took the insulation (a piece of heat shrink tubing) off at the connector. Since the cable was basically very close to the engine, the heat shrink had been pretty well sealed to the insulation on the individual wires; it had been too hot for too long. I found that one pin on the connector that had corroded away but that was simply a battery connection to provide power to a test instrument connected to the cable. I examined the wire and everything I could reach on that cable but couldn’t find anything visibly wrong.

I ordered a new connector and pins and replaced the connector shell and missing pin. The other pins I simply removed from the old connector (extraction tools are wonderful), cleaned them up, and put them in the new connector shell. I replaced the heat shrink with linerless 3M tape. I then secured it with a new tie wrap well away form the engine and where the connector is held so it can no longer flail away with the bumps of the road.

At this point, I was now able to read the engine and ABS data appearing on the data bus, for the first time, with my code analyzer. I still never found a real problem, but my guess is there was a short caused by the combination of the excessive heat by being too near the engine, combined with the weight of that large connector hanging on the end of a cable instead of being properly mounted. But I never actually saw a wire problem to know what I might have fixed.

Since then we have done a round trip back to Texas (about 2100 miles in total) with no indications of a problem. Maybe after another few tens of thousands of miles I will consider it fixed. Or maybe it will fail the next time we fire it up. Stay tuned to see what happens. In the meantime, the ghost has been banished.

Indianapolis, Indiana