Thank you for your time and sharing your knowledge IT IS greatly appropriated!!!Tony, et. al.,
Sorry I'm so late to this conversation. While I am in no way currently associated with FCA or the automotive industry any longer, I was a Software Engineer with Chrysler helping develop their Powertrain Control systems for their 2000 through 2006 Model Year Small Car, Large Car and Jeep Truck programs.
The lure of living in Colorado pulled me away from the metro-Detroit area rat-race.
Everything electronic back then was either already Controller Area Network (CAN) connected or moving that way. So fast forward to today, I would suspect that every electronic component requiring some input or output control is indeed connected to the CAN bus.
For the uninitiated the CAN mechanism is indeed a 'bus'. That means that many 'nodes' can be physically connected together in a common link. This link is made up of generally a twisted pair of wires. One being marked plus + the other being marked minus -. This provides an electrical differentiated signal to be used as the physical link. It is the difference in voltage (rather than the voltage level) that is used to define the actual signalling.
The CAN protocol itself is rather sophisticated and was designed and used as a very reliable (short distance) communication control system. Each and every node within this two wire 'bus' has a unique CAN address that has a built-in priority scheme. Any node can communicate with any other node via a seven byte message (frame). Each frame consists of the source and destination's node address as well as the message payload itself. Any node can originate a message at any time but only the message with the highest priority address will win bus arbitration at any particular instant.
In practice, the communication strategy is typically implemented with a high-priority source control module that manages lower-priority peripheral components. Each controller typically has their own separate bus to talk within their own little sphere of responsible components. The door sensors are monitored by the body controller, the volume knob is monitored by the radio, the O2 sensors are monitored by the engine controller etc. Then the top level controllers are then connected to each other by yet another separate bus.
However, in practice there are many factors trying to thrift away cost. Each and every little piece of anything costs money to be installed. So there is always great pressure to eliminate stuff like 'wires'. Well it doesn't seem like much, every penny saved on volume production generates potentially millions, or more, in savings.
A common practice is to replace the minus (-) wire with the common vehicle frame (ground). Thus you now only need a single wire rather than the more common (and more expensive) twisted pair. However, in so doing the twisted pair reduces, even eliminates, cross induced noise from the electrical signaling, whereas the single wire solution will not. So like everything in nature there are tradeoffs. In this case cost vs noise immunity in regards to reliable message exchange.
Looking at the JL's CAN wiring diagram, it doesn't appear that the single wire approach has been implemented. But this is just a diagram. In practice, some sensors may certainly be. However for the backbone bus, the one connecting all the major controllers together, these should be high quality twisted pair links.
So in order to have so many component faults, this indicates a fundamental signaling failure between the top-level controllers. It very well maybe a high-impedence short that is clobbering the CAN addressing mechanism.
The only good way to troubleshoot this is by isolation. You need to remove each node one at a time, starting at the highest priority components and work your way down. If I was the engineer assigned to go puzzle this problem out, I would be removing the in-vehicle harnesses and bypassing them with an isolated counterpart. Then revaluating the condition of the overall system. Continuing to do this potentially with each and every harness throughout the entire vehicle. But this troubleshooting would be way beyond the skill of an ordinary dealership tech. Not impossible, but access to the harnesses and protocal analyzers would make it rather difficult if not outright prohibitive. Unless you found a dealership owner with very deep pockets willing to Fix an FCA problem. Isn't ever going to happen.
I would further suspect that FCA would highly value your Jeep in order to really (scientifically) understand what went wrong on this particular vehicle.
If they offer to buy it back, please let them. While every problem is solvable, some things are better solved with the bigger picture in mind. Whether this was a manufacturing flaw or a design defect it will benefit all of us to have them look at this vehicle from an engineering rather than dealership perspective. Having the NHTSA involved certainly makes your Jeep more valuable to them than to you.
If I was on the team assigned to evaluate this, my recommendation would be to give you a top-of-the-line Rubicon (or whatever it is you want) in order to do an absolutely sound failure analysis on this particular unit.
Hang in there. Jeep's are certainly more reliable than whatever happened here. I suspect a manufacturing flaw or a pinched or shorted wire to something other than a hard ground. And I suspect it's on the inter-connected controller harness which is likely the hardest to replace. Hence why no one is willing to replace it.
Again I can be all wet behind the ears. But I don't believe so.
Good luck, thank you for being so remarkably understanding and patient. Also, I'd be the first one to contribute to a Go-Fund me page if FCA doesn't own up and do the right thing.
Jeep on Tony. You are certainly one of the good guys. You have all my respect.
I spoke with the dealership late on 12/11 and they have not been able to duplicate the last issues, but they know IT happened because of the OBD information. They requested my permission to let the tech do some “extend driving” with the Jeep in hopes the issue will occur. I have given them permission with a strong warning.
The tech will begin the “test drives” on 12/14.