"Service Shifter" Msg (CAN C Bus errors) - Fixes and parts changed

[Tank the Jeep]

Do you have any pictures, please. I’m really just a one step above a gorilla using a purple crayon.

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[jmccorm]

I realize that some (not all) people reading this might need some appropriate expectations to be set here, so I'd like to offer the following --

The error "Service Shifter Soon" is a "soft" error message (an error where the vehicle can continue operating normally) that is shown when the shifter's error rate exceeds a certain threshold. These errors can be caused by a problem anywhere in the vehicle where the CAN bus exists. (A fault in a major wiring harness is the same as a fault in a tiny connector.)

The only ones I've followed at (that weren't mentioned in this thread) were said to be in a major wiring harness and caused by a chafed wire occasionally rubbing against a ground. One of them also mentioned a problem being somewhere (unspecified) in the ABS system.

Generally, a good dealership will be able to isolate what major segment of the network is having the error. (An occasional intermittent problem will be harder to trace than a more severe problem.) If you (or they) do not have the proper tools, you may find it difficult to unlikely to track down on your own.

A more advanced owner (working without the assistance of a dealer) might isolate all the CAN-C network segments (by unplugging them ALL from a hub like the one behind the glovebox) and measuring each leg, one at a time, and hoping they catch the issue.

Even without a multimeter, if you can say, "everything works fine when my CAN-C hub is fully populated except this one connector", then you can look up that connector's color code in the vehicle's wiring diagram to further learn more about it's function and what harness it's a part of.

Here is some aid for someone who might be trying to use a multimeter to diagnose this (but it may not end up being necessary):

If you are working with a dealer on this issue, and they have spent sufficient time analyzing your vehicle, they should be able to answer these questions:

1. Were you able to verify a CAN-C communications issue?
2. What type of issue was it? (CAN High short to Ground, CAN Low short to Ground, CAN High short to Power, CAN Low short to Power, CAN High missing, CAN Low Missing, CAN High shorted to CAN Low)
3. What segment of the CAN-C network is having the error? (Verifying that they know at least what harness they intend to replace or to spend further time diagnosing. If they can't determine IN A VERY BROAD SENSE where their efforts should be focused, then you might not be in the right hands.)

It is possible that item #2 may not be present when the issue is more sporadic because the ECU would have seen increased CAN-C errors but not yet have been able to attribute it to a particular type of fault. But the responses you hear to question #2 may tell you that your dealer can read and comprehend simple faults as recorded by your vehicle's module(s).

Again, after spending significant time working with your vehicle, if they can't answer these questions, you may have the wrong dealer. You might want to politely move things over to another dealer for a second opinion. (Under warranty, you typically have that right.)

What other symptoms might you see when there's a CAN-C issue besides the Shifter message? You may see a message letting you know that Power Steering has gone offline (making it tougher to steer). You may notice that the TIP Start/Shutoff button isn't working. You may suddenly hear your radiator fan go full-speed without reason (that is it's failsafe mode). You could also see 4x4 or traction control Disabled/Offline messages (although that can overlap with more common faults, such as a wheel speed sensor that's been damaged). And, of course, you may see your dash go crazy and stay crazy. If you're at that point, you might want to disconnect the battery.

If you are told that "there were 24 different fault codes on your vehicle", you might ask for them to summarize which ones they felt were the most significant or of the most importance. If they can do that, it's a good sign that they have a handle on the situation. Having a ton of faults when there's a simple CAN-C bus issue is not uncommon at all.

IMPORTANT POINT: If you have a Tazer, do *not* try to unmarry it while you are having CAN bus faults. That can lead to CORRUPTION of your vehicle's configuration settings. In this circumstance, it is going to be better to physically REMOVE your Tazer than to risk more damage by "safely" unmarrying it first.

Finally, I applaud the effort I see here to find items which are more commonly replaced as part of a repair effort, and I'm certainly going to keep tabs with this thread to learn what more you're able to figure out between yourselves. Hope this information is helpful, and please let me know if I made a mistake somewhere in this small novel I just typed.

 

[gato]

I have updated the status of my issue on another thread, I think. But for completeness, posting here.

My issue was a wiring harness that was rubbing/slightly melting near the transmission bell housing. There was an obvious very sharp metal rubbing point. Because the harness was backordered and hard to replace (almost need to disassemble the vehicle), the tech and I agreed to repairing the harness. He did and all has been well for 5,000 miles, including submerging that area a few times while off-roading. I have put extra tape around other sharp points on the Jeep's harnesses, specially near the radiator/sway bar disconnect area up front.

 

[Bob Burd]

Any chance you could provide a picture of the harness?

 

[gato]

Any chance you could provide a picture of the harness?

I'll try, as it is up there in the bell housing - but to be clear, where mine was rubbing will not necessarily be where yours is.

There are multiple rub/connection points for the CAN Bus C wiring harnesses. These things go to every important/hi-speed module in your vehicle (engine computer, transmission computer, traction control sensors, ABS, shifter control, sway bar disconnect controller, everywhere). It is a like an Ethernet network - noise injection in one place can disrupt multiple systems.

 

[Bob Burd]

Understood. I've crawled under looking before (someone had a connector near the FAD) but didn't spot anything. I suspect there are 2-3 most common places where wear is happening. Would be nice to target those first. So far i haven't seen any pics though.

 

[gato]

Understood. I've crawled under looking before (someone had a connector near the FAD) but didn't spot anything. I suspect there are 2-3 most common places where wear is happening. Would be nice to target those first. So far i haven't seen any pics though.

Said it a better way. Either way it seems like a failing battery is causing enough disruption to the voltage to cause faults while the vehicle is being driven - seems like a system that is not engineered correctly.

Given the fact that the original dual battery system caused Jeeps with perfectly good main batteries not not start (if the aux was bad), and given the location of the aux battery requires removing fenders and breaking clips to service, I have complete lack of confidence that the Jeep's electrical system was well designed. Good engineers simply don't make glaring mistakes like that.

 

[Jeepin' w/ Dogs]

My Can Bus C issues appear to have stemmed from a loose connection on the star bus bar behind the glove box. Wish I would have checked that before I drove half way across the country to get back from Moab after my power steering cut out in Colorado. The technician referenced this star case number https://static.nhtsa.gov/odi/tsbs/2021/MC-10212468-9999.pdf

Very easy connections to check, it takes 10 seconds to pop the glove box out

 

[gato]

My Can Bus C issues appear to have stemmed from a loose connection on the star bus bar behind the glove box. Wish I would have checked that before I drove half way across the country to get back from Moab after my power steering cut out in Colorado. The technician referenced this star case number https://static.nhtsa.gov/odi/tsbs/2021/MC-10212468-9999.pdf

Very easy connections to check, it takes 10 seconds to pop the glove box out

Thanks for posting the STAR.

Yes. That and there is another one like that under the passenger front seat (this one can actually be damaged if you store or push things under the seat.

I checked those two first. But in my case it was an external harness near the transmission tunnel that was chafing.

 

[Buckmaw]

I found my problem.
2021 Jeep Wrangler JLU
Ecodiesel
Stock

Symptoms:
1. "Service Shifter Soon"
2. Random warning lights
3. Loss of power steering

I noticed that even the slightest bump would trigger the malfunction after ten minutes or so.

The fix:
Insulate the wiring harness next to the exhaust pipe at the entrance to the transmission tunnel.
This is on the passenger side of the tunnel. The loom wrapping of the harness showed very minor signs of rubbing, but no exposed conductors were visible.

Wrapped the loom in heat-reflective insulation and secured with stainless steel zip ties.

It's been five days now with ZERO incidents, and I'm calling it fixed.

Good Luck.

 

[grandsrus]

I found my problem.
2021 Jeep Wrangler JLU
Ecodiesel
Stock

Symptoms:
1. "Service Shifter Soon"
2. Random warning lights
3. Loss of power steering

I noticed that even the slightest bump would trigger the malfunction after ten minutes or so.

The fix:
Insulate the wiring harness next to the exhaust pipe at the entrance to the transmission tunnel.
This is on the passenger side of the tunnel. The loom wrapping of the harness showed very minor signs of rubbing, but no exposed conductors were visible.

Wrapped the loom in heat-reflective insulation and secured with stainless steel zip ties.

It's been five days now with ZERO incidents, and I'm calling it fixed.

Good Luck.

Picture of affected area pretty please!!!!

 

[Buckmaw]

Picture of affected area pretty please!!!!

 

[chilsonjay]

Are your error issues still resolved?

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