C Class Mystery Fault

C Class Mystery Fault

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Discussion

MustangGT

Original Poster:

11,641 posts

281 months

Monday 1st April
quotequote all
Hopefully somebody can assist. I have late 2019 C300d 4matic estate. At random times and for no apparent reason it suddenly massively increases fuel consumption and when I stop the car there is a smell of burning friction material from the rear of the car. My local Mercedes garage keeps telling me duff information, presumably because they have no idea. The latest is that it is the knock sensors causing the increase in fuel. Changing from 50mpg to 20mpg is not that..... Nor is it the DPF regenerating, I only do long runs in the car, usually 200+ miles at a time. DPF regen does not smell like burning friction material either. There first attempt at a fix was to reflash the ECU.

I know of one other C Class diesel that had this problem back in 2015 or so. That was a new car and was rejected back to the supplying dealer. According to the owner it is a known fault that Mercedes are keeping quiet.

Any ideas?

Many thanks.

Scrump

22,064 posts

159 months

Monday 1st April
quotequote all
Sounds (and smells) like sticking rear brake caliper. I can’t see what else would give a friction material burning smell from the rear.

MustangGT

Original Poster:

11,641 posts

281 months

Monday 1st April
quotequote all
That's my view too. I am going to reject the car, I bought it less than 6 months ago from this dealer. Worse than useless. They told my wife her A35 AMG could not have Apple CarPlay or Android Auto unless a module was changed in the dash. Wrong again, we downloaded it from Mercedes Me.

MustangGT

Original Poster:

11,641 posts

281 months

Tuesday 2nd April
quotequote all
Dealer has agreed to take the car back, now to look for something else.

donkmeister

8,199 posts

101 months

Thursday 11th April
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Glad to hear it.

Sticking calipers are nothing new, but the problem is that when someone gets one they invariably pick the cheap option of "just unstick it please", which means a swizz with a nylon brush, a few squirts of brake cleaner, possibly some penetrating spray and squashing the piston back with a vice or similar. Next owner inherits a caliper that will almost certainly seize again quickly.

It's a false economy to end up needing to redo the job, including replacing pads and discs when they should have had much more life left, when you can get calipers fully remanufactured for about £200 a pair (albeit without use of the car for a week or two). I found a place that did exchange rebuilt calipers years back, if you can find one of them then it's no downtime assuming you don't mind driving it with a sticking one until it's delivered.

MustangGT

Original Poster:

11,641 posts

281 months

Friday 12th April
quotequote all
Ended up with no arguments with the dealer, although they still claimed to have no idea about it. Agreed a sensible use 'fee' and I ended up with more than I would have got selling it, since the prices dropped during the last 6 months.

Just bought a GLE 250 diesel AMG Line trim. Red with contrast interior, cream and grey/black. Really like it so far. Needed the large boot for my 94-year old Mother's electric buggy etc.