2013 Panamera spurious gear change issue

[JGaudoin]

I'm a new owner of a 2013 Panamera 3l V6 diesel.

Intermittently the when driving on a relatively flat road at around 65 to 75 MPH, just cruising the car will suddenly change down from 8th to 7th gear. If I use the manual selection to place the car back into 8th gear, it will change to 8th but then after a few seconds it will go from manual gear selection back to automatic and return to 7th gear. The car remains like this for about 10 to 15 miles and then returns to 8th gear and no more issues. Using the sport and sport plus modes make no difference, once back in normal driving selection the issue remains for a while.

This gear change issue has occurred around 6 times in 4 months, over approximately 3,000 miles. I've taken it to Porsche Bristol, they say there are no fault codes and are unable to replicate the issue. I've sent them a video of the dashbord while to car is operating this way, but they seem to have no idea of what the problem might be.

If anyone has an idea or has experienced this type of issue and a cure, please let me know.

Thanks

Jim

 

[Stringbag]

DPF regeneration I should think, and completely normal.
The engine in your car is fitted to lots of Cars in the VW stable so i‘d spend a little time researching the issue.
My XC60 did the same thing - basically when it senses the DPF getting full it injects extra fuel into the exhaust and bumps the revs up a bit to burn the soot off. A bit like an Italian tune up without the noise!
https://www.rac.co.uk/drive/advice/emissions/diesel-particulate-filters/

 

[JGaudoin]

Thanks, now you've mentioned it, I had an Audi A5 3L that went into limp mode because of the DPF. I've let Porsche Bristol know to check this and clean the DPF if needed while they have it.

Cheers

 

[JGaudoin]

Just to let y'all know, Porsche Bristol have had the car and checked the DPF which was clean, but cleaned anyway, no error messages seen before or after.

Guess what? The car still does the drop in gear selection even on a long motorway drive at 70'ish for over 100 miles, it suddenly shifts down from 8 to 7 then corrects itself after about 15 miles. If manual gear selection is used to change up from 7 to 8, it self-selects automatic and changes down to 7. The car even does this in the 50mph average speed areas on motorways, down shifting from 6 to 5 then self-correcting after a few miles.

It is so intermittent, maybe once in a 1000 miles, it can't be reproduced and Porsche don't know what the issue could be.

Anyway, if anyone has an idea what could be going on please let me know. The car is under a warranty, so I'd like to get it sorted out before this runs out if possible.

Cheers

 

[MistleyMike]

Smart alternator?

 

[JGaudoin]

Hi Mike

Thanks for your reply.

What do you mean by Smart Alternator? I don't understand how the alternator affects the gear selection.

Have you come across this before, are you a Porsche tech? Your help is appreciated, so I can convey information to the service center, thanks.

Cheers

 

[MistleyMike]

Hello Jim
My completely unscientific answer.........

A smart alternator controls the output voltage based on vehicle operating conditions to reduce electrical load and in turn mechanical load on the engine by the alternator.

If you are travelling for a while at a steady cruise with little electrical load then the alternator can, effectively, switch off. Then when the battery voltage drops to a preset level it will switch on placing an electrical load and thus a mechanical load on the engine. The ECU detects this request for more power and, if necessary, changes gear (to 7th in your instance) to accommodate this. Then when the battery is "topped up" the smart alternator switches off, the ECU detects the requirement for less power and allows the auto box to return to 8th gear.

Much the same as will happen when travelling up hill with cruise control trying to keep the speed at a set level. As the engine "bogs down” the auto box will change gear to accommodate the request for more power.

Mike

 

[JGaudoin]

Hello Mike

Thank you for your reply, which makes sense but how would I find out if my Panamera has a SMART alternator.

It does seem a bit strange that the knowledge base of Porsche Bristol did not suggest this could be a reason for what I am experiencing with the car from time-to-time.

Thanks again for helping with this, it's appreciated.

Regards

Jim

 

[go928s4]

Hi Jim,

I'm no techie so I have no idea whether Mike's suggestion makes sense or not. However, you shouldn't be too surprised by the lack of ideas from your Porsche centre. Most of their mechanics are now taught mainly to read diagnostics and change parts. They learn about other faults by experience and only work on a very narrow range of cars. The fact that nobody on this forum has come back with "Yes, I've had that problem" suggests its a rare one. Once these mechaanics build up some experience they tend to move on and set up as a specialist. It might sound cynical but you are more likely to get an answer from a more experienced mechanic who has worked on a range of cars.

A recent example. I use a local specialist where possible but my car was booked into Porsche for the air-con recall when the car started going into limp-home mode with a series of other warnings so I asked them to have a look at it. They kept the car for two and a half days, diagnosed a coil failure and replaced it (£100 for diagnostics and £140 parts and labour). When the same pattern emerged in January I phoned the specialist who said it sounded like a coil but he would like to check diagnostics before giving a definitive answer. Took car in, 5 minutes to do diagnostics (no charge). 2nd coil failure in 2 months and it seems that once one goes the rest often follow so I decided to do all 7. Once he had parts he changed them while I waited (under an hour), all for under £550.

Looking at the two suggestions to date, it may be worth asking the Porsche Centre (when they reopen!) whether your symptoms accurately reflect either scenario. If they reflect the Alternator suggestion, there is no problem. If they reflect the DPF problem, it may suggest a failed sensor. The sensor detects soot, when there isn't any so automatically goes into regeneration mode. The computer reads this as a normal process so no fault code is generated. Just an idea.

Good luck.

Graham
2012 Panamera Turbo

 

[JGaudoin]

Hi Graham

Thanks for your reply, it's helpful.

I did have Porsche Bristol, check the DPF, sensors and all the diagnostics, no failure indicators were recorded. They have no idea what the fault is, to the point of disbelieving me until I sent a video of the cars behaviour. Anyway, they had no suggestions as to the reason for the spurious changes.

At least now I have your input with Mike's I have something to go on.

The car is great, it runs very well, it's been looked after and performs as expected when needed. The gear change issue is not a problem that urgently needs to be resolved but you know when something keeps nagging at the back of your mind it's nice to get it cleared away.

As you say, I'll have a word with my local Porsche specialists and local Audi dealer to see if they too have any ideas. However, as the gear changing is so rare I can't demonstrate or repeat the issue.

Thanks again and stay safe in these trying times.

Regards

Jim

 

[ScotDoc]

I have the same model as you and my car does exactly the same thing. I suspect it’s DPF regeneration and the car is keeping the revs above 2000 rpm. IIRC the handbook mentions this.

 

[JGaudoin]

Cheers ScotDoc, nice to know I'm not the only one experiencing this. Although I don't do many short journeys, most are over 25 / 40 miles on relatively open roads, it's kind of worrying the DPF is having to regenerate so often.

 

[ScotDoc]

Cheers ScotDoc, nice to know I'm not the only one experiencing this. Although I don't do many short journeys, most are over 25 / 40 miles on relatively open roads, it's kind of worrying the DPF is having to regenerate so often.

It’s pre-programmed in the DME. My fuel consumption drops a little during the process too.

 

[JGaudoin]

Cheers all for your help, I'm pretty satisfied now that the Car doesn't have a spurious gear selection problem. It just shows how valuable PCGB members are to each other, it's much appreciated.

Thanks and stay isolated and safe.