Hello

Hoping someone can help with an issue I've got as the dealership want to wash their hands.

I bought a new GLA 220d in the middle of May and a week later my wife noticed a very strong burning smell coming from the engine compartment after the school run (a 32 mile round trip on mainly fast-flowing A roads). Emailed the dealer, got told to keep our eye on it.

A week later I noticed the same thing, a really strong burning smell and excessive heat radiation from the engine. 45 minutes after arriving home the bonnet was still hot to touch.
Should mention that we normally average around 56-60mpg on the school run but on both those days the average was around 40-42mpg. When I got to school it was 61mpg so the return trip I got only 23mpg!

I called the dealer and he told me to bring it in for a diagnostics. This showed that a DPF regen was attempted on both those days but failed to complete because the ignition was switched off (first time after 18 minutes, second time after 23 minutes). When I bought the car no mention was made of a DPF filer or that it needed regular cleaning.
However, I did a bit of research and it seems the process should normally take between 5-10 minutes to complete.
Begs the question why mine failed twice and resulted in such reduced fuel economy.

There were other issues, dashboard vibration, steering wheel 'clicking', failure to engage 'glide' mode so the garage took it in and held onto it for almost two weeks.
Got it back two days ago and the 'glide' is now working but all the other issues remain and now there is more vibration and excessive play on the steering wheel.

I met with the General Manager and a technician and he gave me a Mercedes technical document on the DPF and explained that even though the process hadn't completed it most likely had blown out most of the soot. That put my mind at rest, sort of. I asked the technical guy how long a regen process should take, he said 20-30 minutes. Seemed excessive, but I left it at that. However, when I got home I read the technical document that states "The regeneration process takes a few minutes and depends on..."
A few minutes, not 20-30 minutes. Alarm bells ringing now so I email the technician and ask why he said 20-30 when Mercedes say "a few".

He got back to me and said there is no set limit for a regen process and sent me a document explaining the short distance trips process. Pointless really because my trips are over 30 miles on mainly A-roads at speeds of 55-65mph so the info he sent is not applicable to my circumstances.

Surely a 32 mile round trip on A-roads in summer should be enough to complete a DPF regen cycle? I have a gut feeling that there is a fault in the system somewhere but they are denying it because there are no diagnostic errors pointing to a problem. They say it is functioning as intended, which I dispute.

I think the process is perhaps completing in a "few" minutes but the system doesn't recognise this and so continues to inject fuel into the exhaust system when it really shouldn't, causing over-heating and the atrocious burning smell on arrival back home, combined with the extremely low fuel aconomy experienced during the regen attempt. The dealership are discounting this possibility, even though the regen process continued for 23 minutes.

I did some calculations too. I was interested to find out how much fuel was injected into the exhaust system to heat it up sufficiently to burn off the accumulated soot.
It turn out that the trip to school (16 miles) used 1.2 litres of fuel and the trip back used 3.2 litres... so the DPF regen process used 2 litres of diesel (£2.50), took 23 minutes and still didn't complete! It doesn't add up to me, but I'm no expert. If this regen process happens roughtly every 300 miles as Mercedes say, then over 3 litres of every 43-litre tankful (7.5% of the tank) is being 'wasted' - basically to heat up the exhaust system.

I think these figures prove that there is a fault and I'm within my rights to reject this car (still within 30 days as the garage had it for 2 weeks).

I spoke to my brother who has had a diesel Skoda Yeti from new (2015) and has never experienced issues with the DPF regen, no burning, no noticeable reduction in fuel economy etc. I'm assuming this is how it should work and I've been unlucky to get a lemon.

I would be grateful for any opinions or insights. Does this seem totally unreasonable? Should I even notice the burning, is it over-heating, why the excessive use of fuel? So many questions the dealership seem incapable of answering.

Obviously I'm very unhappy with my GLA ownership and really want to reject it. We chose Mercedes because our previous car (a 2012 A-Class) provided 9 years of trouble-free motoring and we never noticed any DPF issues. It just worked and I expected the GLA to do likewise.

Thanks for reading and thanks for your help.

RoryG