Serious Gremlin in my Powertrain

[StuartT]

My 42' Imperial is a 2006 with an ISL 400. We barely made it home yesterday afternoon from a trip across the mountains, with the coach finally dying in an intersection as I turned right just a block from my house. After disconnection the car and apologizing to several people unable to get by, I was eventually able to get restarted and limp my way up the hill and into my driveway. So here is what’s going on.

As we were coming over Stevens Pass, the ATC switch was illuminating on and off soon after I got a solid ABS fail light on the dashboard. We pulled off, shut down and looked things over, then restarted. No lights, so we continued and 20+ miles later the ATC light started flashing again, this time every two seconds, but the ABS light stayed off.

Jump 50 miles or so later. Bumps in the road were starting to make the Check Engine light flash, often but not always, concurrent with the ABS light. It became more pronounced as we traveled until one good bump not only flashed these warning lights, the transmission downshifted to a lower gear, than upshift again normally when the light went out. At one point on I-5 north of Everett we pulled off when we lost power. I soon realized we had been bumped into neutral, and when we came to a stop and the lights went out, we re-engaged the transmission and proceeded on.

I got a pretty good clue closer to home when we crossed a railroad track at a slow speed. While the front tires crossing the tracks did not result in lights or shifting issues, the rears sure did and that pretty much pointed to something being loose or making a poor contact in the back half of the coach.

Summary: The digital dash display indicated a transmission communications error. I pulled trouble code 3500 off the first register in the tranny with no other codes captured. 3500 is “Power Interruption, Real Time Write Interruption” with recommendations to check the TCM/ECU and VIM connectors, power and ground connections, etc. Essentially any connector that might be loose or failing. I found nothing but got a lot of dirt in my face crawling around under the coach.

What is really puzzling me is along with th ABS light, it is the Check Engine light, not the Check Trans light, that is illuminating. Never once did the Check Trans light up, but it did throw the code. Go figure.

So far I have not located the TCM/ECU or the VIM for the transmission, nor the engine ECU for that matter. Probably behind a carpeted ceiling panel. I thought they would be in the Forward Run Bay, but not. Any help locating them or comments on where I might have more success looking for the problem would definitely be appreciated.

I have an ISL 400 in this Imperial

[StuartT]

Problem solved. After not seeing B+ at the VIM, I started working my way back through the incoming harness. Didn't take long before I found a 10 gauge red wire broken out of a two pin connector. When I remade the connection, to my great relief all systems fire up and the coach started. The shift selector lit up and all warning lights went out. I later traced that 12V transmission supply wire to a board in the Rear Run Bay, not direct to the chassis battery as expected.

[wolfe10]

Start at the chassis batteries, making sure the connections are clean and TIGHT.

[StuartT]

Actually the solar panel is wired to the house batteries and the alternator is fed from a post on the battery switch.

You can't get a set of dedicated schematics for a 2006 Imperial but I do have a set for the 06 Dynasty and a lot of pages are notated to include the Imperial. While they include among other things the battery and Run Bay schematics, unfortunately there is nothing about the drivetrain comm wiring to the engine/transmission and their respective ECU's. So today the best I can do is try and find these boxes and check all the connectors and pins. I will also trace that 4 gauge wire on the positive post of the engine batteries and see what it feeds. I need to find the Allison 12V and gnd sources.

[jplante4]

StuartT wrote:
Jerry, I did look at the engine batteries and there were only two positive leads, a 2/0 for the starter lead and a 6 or 4 gauge whose destination is unknown. I think that large a wire would be way overkill for the transmission TCM/ECU, but I could be wrong. It is the only dedicated wire there besides the starter feed, so maybe........

Trace that 4 or 6 gauge back. It may be the charging line from an isolator (or solar panel?). Every coach is wired differently. As Mex said, you need a wiring diagram.

[StuartT]

Jerry, I did look at the engine batteries and there were only two positive leads, a 2/0 for the starter lead and a 6 or 4 gauge whose destination is unknown. I think that large a wire would be way overkill for the transmission TCM/ECU, but I could be wrong. It is the only dedicated wire there besides the starter feed, so maybe........

Jim, had the floor plate under the bed up today and no joy. Still betting on one of the cargo bay ceilings. Will need to take down the carpeted ceiling panels to find out.

[Jim]

I have a Cat 3126 with Allison 6-speed and the control boxes for them are on the forward wall within easy reach when the cover is removed from the top of the engine. In my case, under the bed, though some would be under the closet floor. I thought it was pretty convenient to locate them there because of the easy access. I hate to admit the number of times I was in there and didn't really notice them.

I have noticed that HR or Winnebago sometimes copies the others designs so maybe check there?

[jplante4]

I had a similar issue with the Allison. Found the plugs in the bottom of the ECM (shift pad) were loose and the tech that wired the Sahara for the toad left the power wire to the ECM off the lug. It would bounce up and lose contact then fall back down on the terminal. It did that for a few miles and then finally fell off. The shift pad went blank and the transmission went into 4th gear.

I would look for a break in the ECM power wire. It should be wired directly to the positive of the chassis battery.

[MEXICOWANDERER]

You're flying in pea soup
You need a chassis electrical manual from the drivetrain company