7/15/15

Hello,
I finally took the plunge and bought a 2012 LR 4 with 50K miles.
Overall it's a great truck. My only complaint so far is the sound of the engine; it doesn't have anywhere near the "V8 grunt" sound as my Mercedes ML 500 truck but the engine feels strong.
So, among the first things I did was install a trailer hitch and wiring harness. Very straightforward and no complications.
Next, I replaced all brake pads (EBC greenstuff) and rotors (EBC). The original pads had about 50% left but one or more of the rotors must have been warped because the truck would slightly vibrate during hard braking (now it no longer does it).
So here's my dilemma: I could not reinstall the original brake pad wear sensors (already ordered new ones and will replace them soon) so I left them disconnected. The rear sensor was not secured properly and after a few days it got damaged and the "worn brake pads" message appeared on the instrument cluster. Being used to the simplicity of Mercedes vehicles, I assumed the wear sensor only had one wire which is normally open and makes a ground connection (closes the circuit) when the sensor is destroyed due to brake pad wear. Well, as I later found, it's the opposite with the LR 4 (normally closed circuit and opens when brake pads wear). So while I was figuring this out, the truck kept giving me the "worn pads" message so I disconnected the brake wear sensor from it's electrical connector and got all kinds of warning messages, such as ABS malfunction, etc. When I reconnected the wire and then soldered the brake wear sensor's wires together, all went back to normal and no further messages were displayed on the instrument cluster.
Could this have RESET the computer? I'm asking because I immediately took it to the dealer to perform a state emissions inspection and they told me they can't communicate with it yet; that it has to be driven for a couple of hundred miles. This is the typical symptom when either of two things happen:
1) A check engine light appears and is RESET (or any emissions related code) using a scanner/reader or
2) The battery is disconnected (clearing the emissions information).

Well, I did neither of those things but my guess is that tinkering with the brake pad wear sensor resulted in a computer RESET and don't understand why it would happen. I guess the software code in cars these days is so complicated that anything is possible...

Any comments? Ideas?

7/28/15:

I’m at wits end with this vehicle! Even after driving the truck for over 400 miles the LR dealership can't figure out why the vehicle won't allow it to perform an emissions test. They've had it for 4 or 5 days and have worked on it countless hours. Spent time talking to LR tech support and still can't figure it out. Now they're waiting for a LR engineer to show up. In over 15 years of owning several Mercedes vehicles, I've never experienced this before. This is a vehicle which had a pristine service record for almost 50K miles (different dealership) and since taking it to our local dealership it's been nothing but problems. On top of that the airbag light also came on. Couldn't pull any codes with my AUTEL OBDII reader but they claimed it was a defective seat belt buckle. They replaced it, reset the light and now it came back on. I suspect when they replaced the back-up camera wiring harness, something got disconnected/damaged.
I advised them to reflash the ECU or disconnect the battery. They said tech support recommended they RESET the entire vehicle and start from scratch but the vehicle won't allow them to RESET it!
Hope they can resolve this because we truly love the LR4 but if this is what's to come in the future, I'll get rid of it.
Has anyone had a remotely similar problem?
Thanks

Sergio

 

Problem solved. It was a bad O2 sensor. I spoke with the service adviser and told him to have the mechanic look at the O2 sensor data (one of the short term parameters was all over the place when I hooked up my AUTEL scanner and monitored "live data.") but he kept insisting they had done that. He now told me they followed my advice and looked into it more and found the bad sensor. He said it's weird because "it wasn't triggering a check engine light" (they don't always do that anyway). Lesson learned; if you want something done right do it yourself.
The airbag light was due to a loose connector they did not plug in properly.....
Hope this can help someone else in the future...

Sergio

 

Thanks Sergio, very strange one for sure.

 

I've read a lot of posts about a lot of weird problems about a lot of different vehicles over the years, and I am astonished how often the answer ends up being "it was the O2 sensor, but we can't explain it beyond that".

Does anyone here know why a car's O2 sensor seems to be a universal and invisible gremlin ? I'd love a good scientific explanation.