Mercedes 7G tiptronic Gearbox
I'm the proud owner of a 2013 Mercedes E250 CDI, (W212), have owned this car for almost 10 years now. Sitting at 205000km, I was expecting more years of reliable service and great comfort.
Unfortunately for me, 1 hour into my trip to Durban last year, the car broke down at the De Hoek Plaza outside Heidelberg. Luckily for me it wasn't further out, together with my insurance company I managed to pay R2000 for towing the car on a flatbed back to Johannesburg.
Beware
This is the chance you take when buying an old car. Depending how you drive it, you may be in for some nasty surprises (I do drive the car hard when I feel like using all 500Nm of torque).
Below is the story of what happened. I still haven't resolved it yet.
Symptoms
So when I came to a stop at the toll gate, the engine just started shuddering and switched off. It felt like when I had my old Ford Escort and the one spark plug got loose from its seat. It was quite a loud and scary noise. It actually got worse when I put it in Park but I'm not sure what caused that.
Initial Diagnosis
My reliable mechanic came to check the car that evening. He said I should take it somewhere that could read the codes. There was no check engine light which I found strange. The computer readout indicated some flap didn't wasn't closing properly in the engine. My mechanic decided to check the diesel injectors. He found that one was clogged and sent it for servicing. He got it back and it still behaved the same, so he sent the rest but when it got back, didn't make a difference.
2nd diagnosis
His second diagnosis said that it was actually something to do with the gear-box. He opened it up and had a look at the torque convertor. He sent it to a company that reconditions them, and when they opened it up that found that it was badly damaged. R12k was the cost of reconditioning it, which they did. Took about 5 days to do that. Load shedding didn't help with the speed at which it was being delivered either.
3rd diagnosis
The mechanic fitted the torque convertor, and the engine was running smoothly except the gears where not selecting properly. He had his colleague who had the computer do an "adaptation" on the car. This did not help the situation much. He took it to a dealership and they discovered that something was wrong with the Transmission Control Unit (TCU). He used another supplier of reconditioned TCU's to find a replacement. Total cost of this one was R14k (!!).
The TCU was fitted and since the car had now been away 2 months I was eager to get it back. I said I'll take it back and the gearbox can learn to shift while I drove it.
Gears not working
So driving the car around, the gears started hunting. I'd drive at 2000rpm, and the gears would start hunting. It would rev lower, say 1500rpm then go to 2000rpm, then 1600rpm then 2000rpm. I thought this was part of the learning process, however it kept doing it. At one point I was doing 120km/h on the freeway and the car would suddenly rev and then go into a neutral state. I'd have to pull off to the side and start driving the car again from standstill.
Calling in the expert
My mechanic told me to take it to Mercedes Gearbox experts in Alberton. They used a computer and the readout said that the TCU was faulty, as well as all the gears where slipping. The second issue is normally due to incorrect fluid levels, however my mechanic assured me that he had done it correctly, citing the many that he'd done before and the knows the special way to check the oil level. they said that the hunting could be due to a faulty torque converter, so holding thumbs that this isn't the case.
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