GLC 250 - AUTOMATIC TRANSMISSION CONTROL UNIT

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Roberto1975

New Member
Joined
Mar 28, 2024
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1
Location
Kent
Car
GLC 250
Hello MB Club members,

Hope all is well. I am new to this forum so please bear with me if this not correctly posted in the correct area of the forum.

I own a Mercedes GLC 250, 68 Plate, now with 55,000miles on it. Purchased from Merc Dartford, Ex Demo, 800 miles on it, 3months old. I also purchased a 67 plate A200D for my wife, which had about 12,000miles on it, mow 62k, purchased around Jan 2019. Apart from servicing (both under Merc Service plans) relatively hassle free motoring.........until now. Both cars are now out of warranty, from September last year, I have had a multitude of problems mainly with my GLC. But my wife's A class required a new inlet manifold and throttle valve assembly in December, extremely fouled, and the inlet flat and throttle valve where not operating correctly, springing up a number of error codes, not to mention extremely poor fuel economy and power loss. I now use MB of Medway, Rochester, Kent, who are both ex Merc technicians and extremely reputable and good at their jobs. They replaced the above but I am now having to have the exhaust flap actuator replaced as it is corroded and not functioning as it should, or rather as an interim measure, lubricated it to allow it to function. However, decided prevention is better than cure and I am getting that done soon, cost of £575. The inlet manifold and throttle kit cost about £1500 to supply and fit. Not what I would expect at that mileage. I will attach some photos so you can see how bad it was for yourself.

Anyway, back to my GLC, from September I have had 2 new lower suspension arm ball joints, 2 rear shock absorbers/mounts, 2 front shock absorbers/mounts replaced. I hasten to add not through poor driving or hitting potholes but lord knows how it needed all that done to it. The rear shocks were shot one of the mechanics noticed a knocking when he test drove it after replacing the front lower suspension arms. When I was shown the old rear shocks they could be pressed down but would not return to their original position. Also noticed some slight chatter coming from the front OSF suspension, so decided to get those done as well. Apart from being advised that this shock absorber had no shim, it was like driving a completely new car again. I can only put the shim not being put back or replaced when Merc Dartford replaced the steering knuckles under warranty back in 2021. Relieved of about just under £3k for all this to be done.

Now onto the recent faults (as in last week), drove to Dartford for an appointment, pulled into the car park, put the car in reverse and then into drive to move into the parking space, car would not go into drive and engage 1st gear and flicked into neutral, tried it again same problem, tried it again and it then clunked into 3rd. Drove to MB of Medway in a panic and a real sinking feeling in my stomach (car would only engage 3rd, 4th and 5th), had a diagnostic done (can't remember the fault code), but it said something along the lines of reverse gear selector unit. They tried a software up-date and after about an hour, they took it for a test drive and it was fine. I drove it back home was fine and then went out, no problem, drove the car again about 5hours later, was fine, then pulled into a shops car park and the same issue arose. Phoned MB of Medway again and had the diagnostic done again and was told the fault was still there, was informed it was not mechanical, but the Automatic Transmission Control Unit, that has probably developed an intermittent fault. ATF was changed at correct interval, no leaks and was checked by MB of Medway and was fine. When they did the Xentry diagnostic 2nd time round, I noticed something on the pad, asked what that was. Advised it was in the background, but not causing the Engine Light to come up yet and that was the Crankcase Vent Valve. So had no other choice but to get both repairs done, at a cost of £2,260 (£1800 for the Automatic Tranmission Control Unit and £460 for the PCV). I understand the Crankcase Vent Valve is a common problem across Mercs using this M274 engine. Both are fairly big jobs. The gearbox issue requires the transmission casing to removed, oil drained, control unit replaced, new oil and re-programmed with appropriate software and up-dates.

To be fair MB of Medway have been extremely good and absolutely know their stuff. I'm no car mechanic by any stretch, apart from doing my own servicing when I was younger (too old for that now), leave it to the experts. But even they said a car of this age and mileage shouldn't have this amount of problems. I have emailed and phone Mercedes UK customer service, who were about as helpful as a chocolate fireguard, but said they could do a goodwill contribution if I took it to an Approved Merc Repairier for diagnostic and they submit a claim to their warranty team under goodwill, but there is zero obligation or guarantee for them to do anything. Apart from that I explained I've had the diagnostic done so why would I pay more to have it done again to be told the same thing. I am sure that the above bill would be double that if I had the work done by a Merc Dealership, not that I would anyway, more so after putting 2 and 2 together that the missing shim from the front shock was very likely down to them anyway. I have phoned the Motor Ombudsman who really coudn't offer any help, apart from making a claim against Merc Dartford under who sold me the car, but then I would have to prove the fault was there at the time, so nigh on impossible.

I appreciate these are the joys of motoring, but after moving away from Japanese car OEMs (who at the time didn't want to know when I asked if they wanted to do a deal on 2 cars) they clearly didn't want my money. I decided to go with Mercedes as my father and brother both own one (C Class and CLA respectively), both of them have not had any issues and their cars are 9 and 8 years old, apart from I think a lamda sensor having to be replaced.

Has anyone else had this amount of problems, have I got a lemon, is this indicative of Mercedes build, design and component quality after warranty? Is it worth getting a Merc Extended Warranty on both my cars, but that does mean having to take it to a Merc Dealership for the repairs. I'm sure most on here don't have the extended warranty and perhaps just put money into a rainy day fund for these types of eventualities, however, mine has now practically run dry.

I'm am extremely disappointed with Mercedes on what I thought was a quality car and brand, built to be reliable. Apologies for the lengthy post, but a lot to advise, welcome any comments/thoughts on the matter(s).

Attached are the photo's of my wife's A200d inlet manifold/throttle valve repair, absolutely baffling, never seen so much fouling and build up. Wouldn't let me post the video of the inlet manifold control unit, but basicially it shows the old one being manually opened but not closing and getting stuck. Btw I don't use supermarket fuel only branded, haven't done since I had 3 fuel injectors replaced on my old RAV 4 diesel down to supermarket fuel.

Many thanks,

Rob
 

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Mercedes are prone to problems like any car manufacturer unfortunately, the idea that they are some premium brand no longer holds true.

Most Mercedes, BMW, Audi etc are sold as business or personal lease vehicles and after the 3 year warranty a lot of people /businesses then trade them for new

To pick out one comment from your post.

There is no such thing as "Supermarket" fuel. There are around 7 refineries in the UK and all fuel is made to the same British Standards.

Some retailers (including Supermarkets) add their own mix of cleaning agents etc post refining but the base fuel is the same regardless.

You say you only use "branded fuel" yet you still have problems with foiuling etc?
 
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Fuel additives are introduced while the road tanker is under the loading gantry, the data is pre entered into the loading manifest. As stated all road fuels are to a BS spec, poor fuel quality is normally a result of poor underground tankage being contaminated.
 

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