Background:
My daughter decided to do a little "mudding" after cheer practice. Parked to take pictures and the truck wouldn't start (dead battery), so she called. Drove over with cables and some simple tools. We could jump the truck and as long as the cables were on the battery it would run, but if I took the cables off, it would die. Left the truck overnight and grabbed a spare battery from home. Took the battery back, installed it, and it started right up. Started driving it home and suspension fault started. It would deflate to the stops but would still drive. If I turn the truck off, it will air back up to normal and you can drive it but once you hit the magical 30mph, it deflates to the stops again. Hooked up SDD (V130) and I'm met with:



Issue:
The truck will air up to normal height but I get a wonky level. The left side is about 20mm lower than the right. I tried to do a height calibration a couple of times and I could get through some of it but would get programming errors randomly. The CAN_HS wasn't always full of "X" and used to be all green. Found that when I replaced the alternator, the battery cable wasn't attached well and I had pinched the rubber boot between the alternator. Reattached and it seems to charge so getting the alternator wet probably caused the no-start issue originally. When the interface bus was working, it showed wildy varying output from the level sensors. Normal is 0-5V but at normal height, they showed from 0.7V-2.75V.

Request:
It seems as if the CAN_HS is intermittent. I'm good with the mechanical part but I've never played with the CAN interface. I've looked for diagnostic trees for the interface but can't really find one. The real question, where to start? Most of the modules are buried so it's hard to even figure out which one is giving a problem.
1. Is the CAN_HS bus all internal to the cabin? Or are there pathways in the engine bay?
2. The bus is serial (passthru) so if one module fails they all fail? Or is there a way to bypass one to make the rest of the bus work?
3. Shall I just push it into the driveway and start a small fire? (Kidding. Love it and I've done tons to it).

Vehicle:
2005 LR3 HSE, 4.4L, 186k miles. Replaced/repaired (over last 3 years): Transfer case seals, full transmission rebuild, front air shock rebuild, front control arms, Lucky8 suspension blocks, Proud Rhino 2.5" rods, AMK compressor, 18" wheels, Toyo 265/75R18 tires,

 

Before you even mentioned alternator, that was my guess. Although I have had mine submerged and all was fine after.

Have you tried a hard reset? I know you swapped battery, but now that the alt is maybe back to normal try another reset. Brownouts really mess up some computers.

1 - Not sure, but there are ECUs behind the battery that are likely on the bus.
2 - One bad module can corrupt the bus traffic and cause all sorts of issues. So a faulty module will not kill the bus, but will make it behave badly. Really the only way to find a bad module is to try to communicate with each one and find one that returns odd data or will not communicate. Other option is to disconnect the bus at each module. You could maybe map out the fuse locations for the modules and pull fuses too, fuses are often shared but maybe that could at least narrow things down. Maybe even go the full assault method and pull ALL fuses except critical for starting, operation. Then install fuses one by one. Rambling a bit now...

 

After lots of random troubleshooting, I found the "Integrated Transfer Case" module behind the battery to be the problem. I checked the OBDII port pin 3 to pin 11 for resistance, which SDD says should be ~150 Ohms. I got an open on that and started tracking modules. The one behind the battery was bone dry but the connector showed corrosion. Cleaned up the connectors, reattached, and all the modules showed up. The pin 3-11 resistance still shows open but the network integrity test passes (not sure what that's about). Plus, the level sensors now show relatively normal voltages.

I'm missing the cover for the battery compartment so I might try and find one to try and avert issues in the future.