Rear Power Control Module

March 2019 25,000 Miles

There’s a LOT going on in this writeup, and I’m still getting my head around some of it. And, it may or may not apply to your coach per se, but a lot of it will. I know, cryptic…. read on.

It all started when we parked in a campground for a one nighter. Everything worked. The next morning I started it up and had no tail or rear marker lights on the coach and no tail lights on the trailer. All STOP/TURN and everything in the front worked.  Since it was daylight and we were legal we pressed on. When we got on the road we didn’t have dash AC.

We stopped for fuel and when we restarted…..everything worked. It is of course not a coincidence that these three items (the coach and trailer tail lights are separate circuits) broke at the same time and fixed themselves at the same time.

Fuses don’t fix themselves so that was not the issue with the lights. Plus, there are no fuses. There’s a chassis multiplex system with a large smart fuse which covers all the lights in the rear. It’s on the rear Power Control Module. So is the power to the AC clutch which didn’t come on before. After all, since it fixed itself and worked again we didn’t bleed out refrigerant or crater the compressor. It was an electrical issue.

So a lot of researching ensued and it turns out that there was a recall in the making for the tail lights and turn signal, due to failure of the PCM. On social media I read a variety of stories regarding failures along these lines, including the tail light/dash AC problem.

So parked for a few days in a campground in Mississippi I checked again, and had no tail lights. called Freightliner. They agreed that it was the PCM and wanted me to go to a dealer. This would mess up my vacation so after some nudging I got them to send me the PCM to swap out myself.

At 9am !!! a nice campground person knocked on my door and handed me the part. I couldn’t ask for better service…… 24 hours from phone call to part in hand without making ONE step.

Here’s what it looks like….

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Note the large 150A fuse top right. There’s a spot for another below it, and in fact there was one installed on mine…. black which FL tells me is a body builder fuse. That was the ONLY thing I had to transfer over. Every other relay and fuse came installed.

So time to pull the old one out….. here’s what it looks like, right above the recently upgraded pure sine inverter:

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Install is straight forward. Kill the CHASSIS battery switch. I then verified with a multi meter that all was dead. Didn’t want any impromptu welding back there. One VERY interesting point here…. It took a good 30 seconds for the voltage to trickle down to zero on the connections. So, somewhere something is buffering 12V DC. This means that if you want to try and reset the module by de-powering, you need to wait….. I would wait a full five minutes which was at least the time we had it shut down at the gas station in the symptoms story above.

Removed cables and 6 plugs. There’s two types. The white and grey one you see in the picture has a small red tab. It slides sideways and then you push on the lever below and pull the plug. The other type is the black one on the far left which is similar except the red tab pulls down. There’s three more similar plugs on the far side of the box.

Four small nuts and she’s out. Reverse the process with the new box and we have lights!

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Now since this is the old box, ie pre recall I suspect the recall will still apply. Since I also have one on the LBCU and there’s some squeaking in the Belt Pulley System I’ll have to make a date with a FL shop….. at my convenience. This problem got fixed without missing a beat on our trip. I’ll take it.