Stop/Start Issue and Fuel Economy 7.5 PP DSG

[Jordinary]

Hi all,

I recently bought a 2020 GTI Performance DSG after trading in my 2015 GTI PP Manual, mainly because I wanted to switch to an auto and have a slight tech upgrade whilst doing so.

Not long after buying the car I noticed that the start/stop function wasn't working and a message in the car menu said 'vehicle power consumption too high'. I initially put this down to low battery as the car had been sat at the dealership for a month. I mainly do short journeys but took the car out on a 100 mile round trip down the M6 after a week. The next morning stop/start worked at two sets of lights before the same message returned. A week later I did another 60 mile round trip (Mostly M6 again) hoping it would further charge the battery but no luck this time and the message didn't go away. I took the car to a nearby KwikFit for a battery health check and they said the battery was in good health but only 46% charged, but no issues with the battery itself in their opinion.

I bought a Ring smart charger and left it plugged in for about 5 hours this morning before heading out on a short trip to the shops. After this the stop/start actually engaged twice again but then the dreaded power consumption too high message returned.

At this point I am at a loss where to turn. I was starting to think a previous owner had coded the start stop out but the fact that it does sometimes engage makes me thing that isn't the case.

My other issue is that the car seems to do incredibly poorly when it comes to fuel consumption when compared with my Mk7. On the 60 mile round trip to my brothers my 7 would return around an average of 38-40mpg. On the way there in the 7.5 I got 33mpg for essentially a trip down the M6 with a bit of urban driving at each end. I will add that in the 7 I would floor it down slip roads etc and in the 7.5 I am driving much more conservatively as its new to me. On the way back I reset the trip calculator once I got onto the motorway and returned 45mpg.

The economy itself doesn't particularly bother me otherwise I wouldn't have bought a GTI, but the stark difference between this and my 7 has me worried something isn't right.

[Watts]

Hi Jordinary. It sounds highly likely that your gpf needs a regen. This would explain both symptoms. If you do a search you'll find an explanation for how to do it. Just a long run won't always be enough. Good luck, it'll be fine.

[SRGTD]

@Jordinary, welcome to the forum.

As @Watts has said, your poor fuel consumption could be gasoline (petrol) particulate filter (GPF) related. Assuming this is the case, then you might find the discussion topic at the link below helpful;

https://www.golfgtiforum.co.uk/index.php?topic=290349.msg2665390#msg2665390

My post (reply #6) in that discussion topic includes a list of tell-tale signs that may be present when the GPF is going through a forced regeneration to neutralise accumulated particulate matter in the GPF (note; not all of these tell-tale signs may be present during a regeneration).

With cars that are used predominantly on longer journeys, the exhaust system will be hot enough to passively neutralise particulate matter in the GPF and you’re unlikely to be aware when a regeneration is happening. By contrast, with cars used mainly on short journeys such as yours, the engine and exhaust may not reach the optimum operating temperature for accumulated particulate matter to be neutralised passively - if so then GPF regenerations will be forced (a.k.a active) when additional fuel will be used to raise the temperature of the exhaust to neutralise the particulate matter, and this extra fuel usage will adversely affect fuel consumption for the duration of the regeneration process. Assuming your car is attempting a forced GPF regeneration, that probably explains your higher than expected fuel consumption. It might also explain the instance(s) of stop start being inactive as the car’s engine needs to keep running for the duration of a forced GPF regeneration, although there are a number of criteria that affect the operation - or non-operation - of stop start not related to GPF regenerations (from memory, these are listed in the owner’s manual).

Be aware that if a forced GPF regeneration is still in progress at the end of a journey when the car’s engine is switched off, it’ll recommence during the next (and subsequent) ignition cycle(s) until it has been successfully completed.

In the post at the link I’ve posted above, I’ve also provided details in my reply #6 of the process to help keep your car’s GPF clear that you might like to try.

[Jordinary]

@Watts @SRGTD thanks for the replies guys. I've just had a read through the linked post about GPF regens. I do sometimes notice a 'hot' smell that is also present under the bonnet if I open it after a drive.

My only question would be that would the GPF not have undergone a regen on the 100 mile round trip? Edit: Just been reading a bit more about regens on google which says to keep the revs above 2000 rpm. The DSG shifts to 7th on the motorway and sits at 1800rpm. This possibly explains the normal consumption on the motorway and terrible consumption everywhere else. Think I'll put it in sport mode tomorrow and see how I get on.

Nevertheless I'm going to take it out maybe tomorrow if I get a chance and try the engine braking method and I'll let you know how it goes!

[Adam T7]

I’ve used SRGTD’s recommended method a few times, works every time. As for Stop / Start, hate the thing, turn it off as soon as I start up, I can’t be convinced it doesn’t cause premature wear but maybe that’s me being old school.

[Johnytuono]

I've owned a 7.5 Gti DSG for 5 years so know a little bit about it.
The start/stop definitely seems like a battery issue, mine stopped working after saying about high consumption (electric usage). Failing that then it's obviously not charging up so look at the alternator. These things can be checked generally by yourself. Another thing to check regarding the battery is, if its had a new one (if it hasn't then you will probably need one soon) check that it has been coded in.

 The fuel consumption figures you quote seem reasonable to me, for one its got more bhp than your previous Gti and its a DSG box, that will definitely make a difference. If the fan is running after you switch the engine off then that is a sign it's regening. Regening is different than a diesel btw, its not driving down the motorway keeping the revs up to burn the particles off, its driving to a speed of say 60/70 and then taking your foot off the throttle to let the engine drop to say 50 and then it burns the particles off. Do this 5 or 6 times on a run rather than keeping it in cruise control. Btw if its regening then the mpg around town would be around 17/19 ish and it will obviously regen more if you do lots of very short journeys, also there's no actual warning symbol as there is in a diesel.

Hope this helps

[Jordinary]

Just an update from me.

Had to take the car out to town last night to pick up a few things. Traffic was abysmal and I averaged 15mpg over 6 miles. Had a hot/burning smell again. The stop start worked once at the first set of lights and then dis-engaged whilst I was stopped and didn't re-engage again with the usual message appearing. Left it on charge for the rest of the evening once I got home.

Decided to go out for a drive this morning and test out the tips from @SRGTD. Let the oil temperature warm up to around 90 degrees and then let it rip on a few country lanes in sport mode. Whenever I would find a straight section with no cars behind me I would floor it to 60 and then switch to manual mode and drop it into 3rd or 4th gear and let the car slow to about 30. I did this a few times before joining a dual carriageway near mine with a bunch of roundabouts on it. I had a bit of fun gunning it up to speed and then before each roundabout I'd engine brake again until I had to intervene with the actual brakes. From the first stop on this journey I had the message saying about vehicle power consumption being too high on the stop/start screen. I finished the run at a local supermarket and was surprised to see I had an mpg of 30.8 for the 26 mile journey even after driving like I stole the thing compared to usual (Bear in mind I got 33mpg on a gentle motorway run using 7th gear last week). The stop/start message was still there which concerned me but when I got back to the car half an hour later the message was gone and it hasn't returned all day.

The drive home from the supermarket I have done many times in the last few weeks and the best I could muster was around 27mpg. This time I got 35 without even trying.

A few hours later I drove to my dads. He lives literally 1 mile away and it was a cold start on the engine this time. Previously I'd be lucky to see 18mpg and I managed 27 this time. The entire time stop/start has also been working.

I have to say that so far the advice about the GPF seems to have done the trick. I will keep an eye on it all over the coming days but fingers crossed the problem is solved.

It seems mad to me that the car does not make you aware of this issue at all with any messages telling you it is trying to do an active regen and as far as I can see it isn't mentioned in the manual either. Its also crazy just how much extra fuel it is burning to do it. I've basically dumped a ton of petrol the last 2 weeks that if I had known I could have avoided. It makes me wonder how many people are just driving round on short journeys with a GPF equipped GTI all the time burning a load of fuel because they have no idea the car is trying to regen, then on long journeys sticking the car in eco mode and not hitting 2k revs or doing any engine braking. A new owner might just assume this is a normal amount of fuel use and its only due to me having the mk7 that I thought something seemed off.

A few images below showing the message I am now getting and the last journey:

[SRGTD]

@Jordinary; thanks for the update.

I’ll keep my fingers crossed for you - hopefully the issue’s resolved.

[Jordinary]

Drove in to work this morning. Definitely seeing improved mpg, its up by about 6mpg on short trip in traffic. No burning smells etc.

However, the stop/start has gone again and the power consumption too high message has returned. Not sure where to go with it now.

If a new battery was not programmed in would the stop/start never work or could it work intermittently?

[Johnytuono]

No, it would probably overcharge as it would be thinking it was an old battery, I'd put my money on you needing a new battery, mine went after about 6 years which is a good age for a battery.