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Discussion Starter #1
So this post is mostly for people who DIY their maintenance and repairs and MB mechanics in the group. And it is a long post!

I have been building, racing and working on cars my entire life and can rebuild/repair most anything, but this MB....

Here are my problems listed with questions below each one:

1. 4 matic rear differential - went out at about 38-40k miles, just after warranty went out. It still works, just makes a terrible clunking sound. Disconnected the control wire to shut it up at about 70k.
I refuse to pay 5-6k for a new unit that may not last any longer or 2-3k for a used one that may be on the verge of going out.
Q. Has MB upgraded/updated this unit on the newer ones?
If so, will the upgraded/newer units fit a 2014?
Has MB started releasing parts to repair/rebuild these units yet?

2. I’m getting certain messages on the display such as: “pre-safe functions not available see owners manual”. When this comes on, the power steering goes out and it is difficult to drive.
Q. Is this pertaining to ABS sensors? That is what our local stealership told me a year or so back when this happened the first time. They changed the sensors for free because it started just after they had done maintenance(like on the way home). They told us if it happened again we’d be responsible for the cost.

3. Code C0034 Engine code - Right front wheel speed sensor
Q. Is this what is causing the problems in 2. above?

4. Code U140A Engine code - Unknown Issue
Q. Any help with this would be greatly appreciated.

5. Code P061B - Engine code - Control Module
Q. We have changed the main battery in the car a year or so, but not the secondary battery. I’ve read the stories on this forum about issues caused by this battery, could this be causing this issue? Or is it something else?

6. Code P0792 - Engine code - Inner shaft speed sensor. From the research I have done this is a problem in the transmission. We started having issues with the trans and that is why we parked the car. It started with a message on the display while we were traveling at highway speeds that said, “no reversing”. The next time my wife drove the car the car would not shift and stopped moving in all selector positions. I trailered the car home. When I got home I unloaded the car under its own power. I have moved it around a few times since. Fluid is full and has had factory maintenance.
Q. Any info on this problem would be helpful.


I don’t really have a good system to diagnose issues from the OBDII port. I can read them only, and can’t clear them.
Q. What is a good (reasonably priced) DIY system that will allow me to diagnose/and reset the system?

I know I have spewed some hate on this forum for these cars, but the truth of the matter is, I really love the car! It’s my inability to reliably repair it that frustrates the crap out of me!

Please, any help would be appreciated. If you feel the need to belittle or post hateful comments, I’d appreciate you going elsewhere.

TIA!


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Knew you would come around pal
Thats A LOT to work out though a couple of those might be related
Forget about the diff for now looks like the TCU and/or gearbox needs help
Can you check gearbox oil condition? How old is the current fill and how many miles?
 

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@tritron
Long shot here ... have you peeked at the gearbox and powertakeoff unit yet in your trek?
 

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Discussion Starter #4
Knew you would come around pal
Thats A LOT to work out though a couple of those might be related
Forget about the diff for now looks like the TCU and/or gearbox needs help
Can you check gearbox oil condition? How old is the current fill and how many miles?
Yes, I expect that at least 2 are related.

The rear diff is last priority.

I am not around the car at the moment. Went get back to it in a couple of weeks I will check my service records and check the fluid.


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tritron has been tearing into the engine for a rebuild ... so hopefully also has some comments on the gearbox (hence my long shot hope)
 

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I am working on fixing my car engine. It seems that part from 2018 are interchangeable with 2014. Well looks like your issues are caused by abs sensors For example code U140A - The right front wheel rpm signal sent from the traction system via the CAN bus is implausible. I would get rear deff used from 2018 car in front colision.
 

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Is your transmission software up to date ? It could be issue shifting into 7th gear
Transmission intermittently fails to shift, vehicle jolts in higher gears. FC 92177 or FC 92100 is stored.
Topic number LI27.60-P-058317
Version 2
Design group 27.60 Gearshift, control
Date 03-10-2014
Validity Vehicles of model series 246, 176, 117 with automatic
transmission 7G-DCT
Reason for change Dual clutch transmission software update with
subsequent normalization and adaptation

Complaint:
Transmission intermittently fails to shift, vehicle jolts in higher gears.

The dual clutch transmission (DKG) control unit contains the stored FC 92177 or FC 92100 ("The shift valve of the internal shaft has a malfunction. The commanded position cannot be reached").
In the extended fault freeze frame data it can be seen that this fault was set in 7th gear - see Figure 1 in attachment.
 

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Discussion Starter #10
I am working on fixing my car engine. It seems that part from 2018 are interchangeable with 2014. Well looks like your issues are caused by abs sensors For example code U140A - The right front wheel rpm signal sent from the traction system via the CAN bus is implausible. I would get rear deff used from 2018 car in front colision.
Ok, so I need to replace the right front wheel speed sensor. Should I replace the left as well(the dealership stated this when they changed them before)? Does this require being taken to the dealership for reflash/programming?

So the 2018 rear diff works on the 2014, thanks. Does this require reprogramming?


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Discussion Starter #11
I’m not too well up to date on the newer transmissions and controls. I’ll probably have to study this manual for a while.

I’m not sure about sensors needed changing, I assume by the codes there is a speed sensor in the transmission that is failing.


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Is your transmission software up to date ? It could be issue shifting into 7th gear
Transmission intermittently fails to shift, vehicle jolts in higher gears. FC 92177 or FC 92100 is stored.
Topic number LI27.60-P-058317
Version 2
Design group 27.60 Gearshift, control
Date 03-10-2014
Validity Vehicles of model series 246, 176, 117 with automatic
transmission 7G-DCT
Reason for change Dual clutch transmission software update with
subsequent normalization and adaptation

Complaint:
Transmission intermittently fails to shift, vehicle jolts in higher gears.

The dual clutch transmission (DKG) control unit contains the stored FC 92177 or FC 92100 ("The shift valve of the internal shaft has a malfunction. The commanded position cannot be reached").
In the extended fault freeze frame data it can be seen that this fault was set in 7th gear - see Figure 1 in attachment.
I do not know about the trans software. It was last at the dealer in May of 2019.

I’ve never noticed it having any problems shifting until the day it failed and we parked it.

You kind of lost me on the rest of that.

What attachment? I don’t see one on your post.


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see? told ya tritron is the new wise guy :p

oh @tritron if you want the more recent workshop books try emanualonline ... that was the first thing i did back in 2014
 

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Discussion Starter #14
Ok, finally got back home where I can start trying to figure this car out.

So, before I left I put the car on my battery maintainer along with my Mustang. I went out to my shop last weekend and lowered it down and started it up. All check engine lights are now off and the car is driving fine! The battery is fairly new, so I’m thinking it has nothing to do with that. But, what about the accessory battery.
I probably need to change it anyway since it’s the original and is 6 years and 102k miles old. What is a good battery to replace it with?


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Oh good! Sounds like a “good start”

I always can find cheaper main alternatives but that little 12v12ah never comes cheap

But amortize it over the last 6yrs thats maybe $30 a year so ...

Typical replacement is the Fiamm oem unit
 

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I’m not exactly sure what you are asking/saying here.


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I was trying to say to check the unit in trunk that controls rear differential. You said you disconnected electronic and it stopped. I read that unit goes bad and causes issues. I wonder if rear differential in your car is same as qx30 gla250 the part is cheap arround $500 used on ebay.
 

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Discussion Starter #18
I was trying to say to check the unit in trunk that controls rear differential. You said you disconnected electronic and it stopped. I read that unit goes bad and causes issues. I wonder if rear differential in your car is same as qx30 gla250 the part is cheap arround $500 used on ebay.
I will do this. How do I check it?


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Oh good! Sounds like a “good start”

I always can find cheaper main alternatives but that little 12v12ah never comes cheap

But amortize it over the last 6yrs thats maybe $30 a year so ...

Typical replacement is the Fiamm oem unit
I’ve found MB replacement for about $139.


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