W221 7G shifting issues

[mogul]

My 2013 W221 S350 Bluetec is on 94,000 miles.

Transmission fluid has been changed twice (at 50k miles and again last year at 90k miles).

I recently noticed stop-start never showed up and then, the shifting behaviour of the ‘box was erratic and occasionally it wouldn’t change up through all the gears…

I began to think it could be a battery issue so I replaced the main battery with a Bosch S5 and it’s a lot better.

Stop-start is back and it often shifts exactly how I would expect it to.

However, there are days when it doesn’t want to shift up through all the gears…

Is this potentially related to the aux battery!

I might try the Yuasa version BATT-NP1.2-12-YUA

Has anyone had any similar transmission issues that were resolved in this way?

Any issues with the Yuasa? There is a note to say that the terminals are reversed but otherwise, it looks as if it is the right battery for this application

 

[LostKiwi]

I believe the Aux battery is only to allow the gearbox to go into park if the main battery fails.

 

[AMGeed]

I'd check the Ah of your present Aux battery before buying that Yuasa one.
IIRC the Aux battery is around 12Ah, not 1.2Ah

 

[mogul]

Enlarge the eBay image I attached…

“ Genuine Mercedes-Benz Auxiliary 12V 1.2Ah battery N000000004039 “

And check out the Yuasa website for compatibility…

Yuasa UK - The world’s leading battery manufacturer

Find the right battery for car, motorcycle, automotive, industrial VRLA and all other standby power applications. For quality, reliability and performance choose Yuasa batteries.

www.yuasa.co.uk

We are of course talking about a facelift car with the aux battery located in the dashboard and not the original version where a larger battery was located in the rear (between the rear seats and the boot).

If my 9 yr old aux battery is not likely at fault here, what else might be behind this intermittent, strange/restricted shifting?

P.S. I have also tried the transmission reset operation which didn’t do anything but I understand that is more to do with resetting the shift behaviour between relaxed and sporty modes and less about resolving issues like mine where occasionally, it will refuse to change up beyond 4th or 5th for no obvious reason and then on the next journey, it’s all back to normal..

 

[LostKiwi]

It's cheap enough to try I guess.

 

[mogul]

So. Packing my diddy £9.99 Yuasa 1.2Ah aux battery sourced off the ‘Bay, I proceeded to remove the (RHD) driver’s side / off-side / dash-end fuse box cover and undo a few screws to move stuff out of the way and I found the metal cradle that I expected to hold the OE battery, but the cradle was empty (and there were no loose connectors)

Am I going to find it on the passenger side / near-side, or somewhere else?

My car is a very late ‘13 W221 RHD Bluetec.

 

[mogul]

 

[mogul]

So my late W221 Bluetec with Stop-Start Aux. battery is behind the rear seat and it’s pushing out 12.97V so I’m guessing that it isn’t the cause of my intermittent shifting woes.

I actually have full MBSH on this so might let them plug it in and diagnose…

 

[mioba]

How are you getting 13v out of a 12v battery. Is the engine running.

 

[00slk]

Have all stop/start functions have 2 batteries?

 

[mogul]

I got 12.97V with the engine off! Have yet to read it with it on.

 

[mogul]

…and now >14.5V with the engine running.

 

[mattkh]

....... issues like mine where occasionally, it will refuse to change up beyond 4th or 5th for no obvious reason and then on the next journey, it’s all back to normal..

Try to focus on the conditions the engine and gearbox is at when it happens.
Two journeys are never the same, there are so many differences eg engine temp, gearbox oil temp, outside temp, traffic, etc.
Next time it happens, make a note of all the variables you can think of.

 

[mogul]

200 miles driven today, up and down the M5.

Faultless over the first 100 miles and then after a 2-3hr pause I set off homeward bound and it wasn’t shifting above 4th again!

However, I knew that if I pulled over, switched it off fully for a few seconds, and restarted it, there was a good chance that it would sort itself out - and it did phew!

(43mpg avg.)

 

[LostKiwi]

Find a decent Indy (Steve@Avantgarde near Bristol springs to mind) and have the codes read. A dealer will charge around £200 to do it, Indy's are much cheaper and generally know these cars better too having worked on them for years (unlike the kids they 'train up' direct from school in the dealerships).

 

[mattkh]

after a 2-3hr pause I set off homeward bound and it wasn’t shifting above 4th again!

Was the weight in the car the same as on the outward journey..?

 

[mogul]

Just me and my son this time - but it’s often just been me.

I have heard of Avantgarde - will think about it. I’m based near Newton Abbot and have had a ‘mixed’ experience with a specialist there although there are a couple of others within the local area that I haven’t tried yet.

 

[V6Matty]

MBS over in Southampton as well if you travel that direction at all, as @LostKiwi mentions these two Indy’s are worth the travel in getting a root cause resolved first time