2015 LR4 having a meltdown at random times. Related to High Speed CAN BUS. Need help!

Tom Garrett

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I recently had my windshield broken on a cross country trip. When I got home, I had the windshield replaced at the Land Rover dealer with factory glass. Within a day or two of having that done, the dashboard would light up with all sorts of messages and warnings. Very often the car will go into a limp mode, lower the suspension, and limit speed. I tried to post a video of the dashboard when this happens, but this site won't seem to allow it. I took the car to a reputable indy and they recommended a battery and alternator replacement based on the fact that the battery was over 4 years old and there was an error message for the generator(error report attached). I have now had the car at two independent Land Rover shops and no one can find the issue. The errors are all related to the high speed CAN BUS. After the alternator was replaced, the message related to the generator has gone away but the car still freaks out at least once a week. If I disconnect the battery leads and connect a wire between the leads for a few seconds, reattach the leads to the battery and wait for a bit, it usually clears the dash with the exception of the check engine light. The check engine light will usually clear after a couple times of starting and stopping the car. It happens at completely random times. Sometimes it is shortly after starting and sometimes it happens after driving 100 or more miles.

Based on the fact that this started almost immediately after the windshield was replaced, I was wondering if anyone knew if there was any wiring in the A pillars, under the lower windshield cowling, or where the mirror connects to the windshield that could be causing a problem with the High Speed CAN BUS. I am hesitant to go back to the dealer until I know more as I'm sure they will try to deny any responsibility.

Any information/guidance would be greatly appreciated. I love the car but if I can't get this figured out, I think I'll need to trade it in...

It is a 2015 LR4 HSE and has approximately 68000 miles. After the windshield replacement at the dealer, I had the following maintenance items performed
Front and Rear Crossover pipes
Thermostat
Water Pump
Battery/Alternator
 

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jlglr4

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That is one hellava long list of codes. I don’t know of any wiring that would have been compromised by the windshield install (although I see a code that indicates your windshield mist sensor (auto wipers) might not be working properly, but that shouldn’t cause these problems).

I generally look for “P” and “B” codes and get those sorted first as those generally relate to hardware problems that can give rise to the comm codes (“U” codes). For instance, I see a parking brake module related code P1707. The parking brake module interacts with the transmission control module somehow (I don’t know the details) and can cascade other codes. In fact, a malfunction parking brake can cause strange noise when starting the car or putting it into and out of gear (even if not using the parking brake at all). Might check your parking brake to make sure that’s working correctly, and recall if you are hearing any strange screeching noises at any time (regardless of whether you are using the p-brake).

There also is a code relating to a vehicle speed sensor. I don’t see that particular code in the manual, but it could relate to a wheel speed sensor (one at each wheel, part of the ABS system) or the crank position sensor. But I don’t know how to take that diagnosis any further.

There is a steering angle sensor code, and I’ve heard of this sensor creating these kinds of issues. I don’t see any code from the brake pedal sensor, but that also is a notorious cause of problems at least on the older cars.

Finally, water ingress into the passenger side dash or floor area has been known to cause all sorts of these strange electrical problems. Typically, this is the result of a clogged sunroof drain, but could also be from a water coming through a badly cracked windshield (not sure if that is relevant here or not).

Since you have a record of the past codes, you might try clearing the codes and see what comes up first the next time the problem arises. Not sure if you have a code reader that will let you do this.
 

Tom Garrett

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I did have a water intrusion issue on the passenger side due to a broken sunroof drain tube. I had the mechanic inspect all of the wiring that runs along the passenger floor. He indicated that I resolved the problem quickly because there were no signs of any water issues. He even wiggled the wiring while the car was running to see if he could get it to act up but no luck. I had them pull the junction control box from under/behind the glove box because I thought corrosion might be an issue if that got wet. All looked good and no sign of water damage. I will check the parking brake and see if it is functional and to see if it causes the issue but I don't typically use the parking brake. I had the oil changed yesterday after they spent time reviewing it. I have driven over 150 miles and the problem has not occurred again but I'm sure it will. The mechanic cleared the codes and I bought a code reader so the next time it happens I'll report back. Thanks for your input.
 

Michael Gain

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It's been awhile since I've been in the LR4 engine bay, but here is my advice.

Check the driver-side battery box. The TCM is there; and the abs and transfer case have electrical connections there. Also, that is where the main wiring harness from the engine compartment enters the cabin on its way to the BCM.

The dealership most certainly had the opportunity to mess up the cross engine wiring loom, from the passenger (PCM) to driver side battery boxes, when pulling the lower windshield cowl. The auto sense wiper sensor is also attached to the windshield. Either they broke it upon re-install, or forgot to reconnect the electrical connector.

If I were you, I would take it back to the dealership that did the windshield replacement. If they are shady, they will charge you for the diagnostic and repair. If they are honest, they will own the mistake and repair it for you at no charge. Regardless, it will be repaired and you can enjoy your truck
 

Tom Garrett

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Thanks so much Michael. That seems very plausible and I'll follow your advice. Do you know if any of those modules are on the high speed CAN BUS as this seems to be where the problem is located. Also, do you happen to know where the auto sense wiper connects to the windshield? Is it at the bottom or up near the mirror? I really appreciate it. You give me hope!
 

Michael Gain

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Not a problem at all. Yes. All of the car's modules communicate along the high or low speed canbus--between each other, receiving input from various sensors, and to the various system outputs available to the driver. The auto sense sensor should be on the driver side of the mirror. The passenger side cover houses the humidity sensor if I remember right.
 

ltg123

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This may be a long shot, but the lr3's would do something similar because of the brske switch shorting internally. It's a Ford fusion part like 23 bucks and super easy to change. And the codes would have nothing to do with anything in the brake circuit. Suspension would drop, linp mode, etc. If it's still the same part, I would change it.
 

Tom Garrett

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FOLLOW UP...
I took the car to a trusted mechanic in Bozeman to try and diagnose the problem. He spent a couple of hours with the car and cleaned a lot of electrical contacts. I didn't get an exact list of what he cleaned, but the car is now behaving properly.

Thanks to everyone who took the time to reply as I really appreciate your counsel!
 

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