Hey all, we just finished a 6000 KM trek with our LR4, which it handled beautifully. About half way we randomly got thrown into LIMP mode, where we checked fluid levels and noticed that we were a touch low (oil was a quart low). Topped it off and everything worked great besides the fuel sensor (which randomly went to full on breaking to empty) and the special programs were offline, which I chalked up to be unresolved codes that had to be cleared.

We completed the trip with no other issues. A few days after arriving at our destination, we got an ABS fault followed by all lights coming on and dropping into LIMP mode once again. The symtoms are:

• Transmission not shifting
• Gearbox Fault
• ODO Meter randomly dies and comes back online
• ABS warnings disappearing and re-appearing
• Suspension lowering and raising
• Seats unable to move for longer than a second at a time (only if the ODO Meter is not working)
• Doors not locking/mirrors not folding
• Last error that usually appears is charging system fault

This is what we have checked:

• Battery and alternator are good
• We unplugged all USB devices incase they were causing low amps at start
• Good battery connections
• Breaks and fluids were fully serviced before we left, and they are looking good
• Suspension is working great
• Gas cap of course
• Rotors are looking a little worn which did concern me

As a small note, when we got tires last it appears that they did not install the pressure sensor correctly on one tire, which throws errors randomly. I don't believe this to be relevant but I am aware of how fickle these machines are.

Our last step was buying a diagnostic tool and seeing what we get. Here are the results!
Before clearing we got a lot of codes, but the few that stand out are:

• P0500 Speed Sensor A
• P057B Break Pedal Position Sensor
• U0402 Invalid Data Received From Transmission Control Module

I believe the communication codes are being thrown because of the Speed Sensor, which I have seen posted about a few times, but the others also make me weary that we are going the right direction.

After clearing the codes, we are still not getting fuel gauge and no special programs, and we are seeing these five codes (until we drive for 20 or so minutes where the codes are once again thrown):

• U0128-00 Lost communication with parking brake control module (PCM and TCM)
• U0138-00 Lost communication with all terrain control module (PCM and TCM)
• U0151-87 Lost communication with restraints control module (PCM)

I can't seem to find anything on the these codes which would be conclusive, but I would assume that the parking break control module could be the root of my issues. I am a rather new DIY with rovers and most of my DIY hobby mechanic knowledge is around old box engines in my 83 Westfalia, so I just want to make sure that I am on the right track.


TLDR:
Would a speed sensor throw the car into limp mode, could worn rotors cause this issue, or would parking brake control module be the culprit?

Thanks in advance!

 

Back up a sec… quantitatively define “battery and alternator are good”.

 

I have checked voltage with a multimeter following these steps:
First checked battery on its own, and then after starting, and validated with high revs and having fans/lights all on.

And then I also checked with my diagnostic tool which also gave me a green light.
I am happy to do more testing if suggested!

 

Sorry to bother you with this @moogs. I just like to rule out the easy things first: Could you please take a reading following a rest of 6 hours on your battery (no charging or running the engine, etc.)

 

Don't be sorry at all, I last started about 5 hours ago so in an hour I will give it one more go.

 

@guy Waited the six hours (last started around 9AM EST, tested at 4PM EST, no charging or anything) and we got a reading of 12.3 which should be good?

I really hope it is something easy, as we did have -50 weather during the drive down in Canada which could have affected the battery.

 

I’m afraid you stand corrected. A lead-acid battery should read 12.6v. An AGM from 12.6 - 13.1.
Your battery contains less than 50% of capacity. And this could be the source of your communications between modules woes.
In order to rule it out it must be corrected.

Think of it like this, the electronic systems of vehicles of today are managed by modules. These modules have high electric voltage (and current) requirements. With a significantly degraded battery source, there is not enough “electric fuel” to power these demanding components. Even in the workshop manuals it is emphasized to rule out the electric source, first.

FYI, you’re not alone. Many are unaware of this fact. Me, I replace the battery if when fully charged only reads 12.4v.
Also, be aware, rarely is a newly purchased battery fully charged. I would fully charge a new battery before installing in the vehicle.

Truly.

 

Holy thank you I will get one first thing tomorrow! I ruled it out as we just replaced it last year, and everything I read said between 12-13v. I will install tomorrow and post the results!

 

Confirm what I say. Check this out: https://www.testingautos.com/car_car...r-battery.html
or the interstate battery website. There are a few good sources.

And while the battery is disconnected, touch the + and - leads together. This will cause a reset of non-persistent failure codes.
Then connect the battery.
Be sure all accessories are turned off.
Then start the vehicle this way: with foot off brake press and release start button.
Wait for all dings, chimes whirs to stop.
Depress brake and press start button again.
Go for a drive. rpms up and down, speeds up and down for 30 mins. This allows the ecm and tcm to relearn your driving habits and adjust management settings accordingly.

 

So I think that solved the main limp mode issues that we were seeing which is fantastic! No ABS lights and all of the engine lights as before.
However, the fuel gauge and Terrain Special Programs are still offline with the same codes.