Automatic gear doesn't shift + SBC H unavailable?

[frustratedwithmechanics]

Hiya

Main issue description
A few days ago I was driving normally and when stopped at a red light I pressed down hard on the brake to activate the hold. I got an error message "SBC H unavailable".

A couple minutes later I noticed that the automatic gear wasn't shifting. Not sure what gear it was stuck in, perhaps 2nd? It was impossible to go higher than 40 mph or so. Also when I tried to reverse into a parking spot it wouldn't let me engage reverse: the only way I could do it was lift my foot off the brake and then put it in reverse! Or, alternatively, turning it off and on again.

Additional symptoms
- The gear problem seems to come and go (some days the car runs find, and some other days it has the issue).
- As best as I can recall the "SBC H unavailable" issue is always there now.
- The gear indicator on the dashboard also is acting funny: usually when this problem is present it won't show "D" (it doesn't show anything). And the other day I put it in D but the dashboard said it was in P!
- I can't manually change gears when this problem is present.

Help?
I've taken it to Mercedes and they are talking about a 4000 GBP repair, changing the gearbox and "a hydraulic unit" (they refuse to explain which hydraulic unit or provide a part number - yes, seriously). However when I search online for similar issues there are loaaaads of different explanations to this problem, many of them involving replacing a 10 dollar part...!

Can someone help me? I'm not at all confident that the mechanics at Merc know what they're doing (or that they're acting in good faith) and I really don't want to spend this much money on a car that is barely worth that much...

Thanks a lot

 

[Blobcat]

Hello and welcome,

First thing I'd be doing it checking battery voltage - next get codes read and see what SBC pump activation is like - they can be reset and may have been done in the past without your knowledge which can lead to sudden loss of braking ability.

 

[Flyinspanner]

Gearbox is in limp mode.
that’s why it’s holding 2nd gear.
They often kind of clear themselves when switched on/off, but it will get worse… till you get stranded.

That is often the electroplate failure. (Speed sensor on them dies).

post up the general area where you live and ask for recommendations for a nearby Independant MB Specialist. - you want one who has the full STAR diagnostics system.

STAR interrogates components to a deep level and can save money in the long term.

A good indie will get it fixed for a fraction of a dealer. (And usually take more care).

about 4 yrs ago my electroplate was around £500….

 

[ajlsl600]

As above. Faulty speed sensors can cause a number of issues as many operations/functionns require that information.
But as advised given possible outlay. Get the codes read and go from there
Owning these cars without having xentry /star and or icarsoft and being familiar with it is likely to turn into an expensive experience.. Mine stays in the car! Don't ask me why.......
Modern electronics are NOT reliable and I would say that is verified by the % of electrics, electronic posts, requests on. Here.
For example a faulty speed sensor, can prevent a shift, or a shift, forward, reverse as sensor is saying transmission output shaft is still turning. When in fact it is not. The fact that benz make sensor part of electro plate is shite design as all sensors I ever see can, do go faulty for often, unexplainable reasons. Near all on my vatious brand machinery are, thankfully individually replaceable .
Get the codes read . Look historic or active, as sensors degrade they can often show up as OK, then not., hot and or cold.

 

[alexanderfoti]

The D disappearing from the dashboard points to a selector module fault. Not inside the gearbox itself although a diagnostics session will need to be completed to confirm.

 

[Snake Charmer]

The hydraulic unit Mercedes refer to is likely to be the SBC unit.

 

[alexanderfoti]

They also refer to the valve body as the "electrohydraulic" control unit.

 

[ajlsl600]

All makers dream up their own terminology for various bits, functions can be a real pain when dealing with multiple makes I often hav to take another aspirin, or refresher course that's why I NEVER clic next or proceed or OK until I read each pGe 2,3 times..

 

[ajlsl600]

I currently have jcb. Cat, Iveco/Astra, Hitachi, atlas copco, doosan and Cummins diagnostics all on different tough books plus icarsoft, xentry at home. Tho xentry is away for recovery. I can tell you that if not really careful one can really f up ones day with that lot and at least half the time is trying to find out, remember how each system works. With exception of cat et. With which I am fairly familiar fairly

 

[Craiglxviii]

Gearbox is in limp mode.
that’s why it’s holding 2nd gear.
They often kind of clear themselves when switched on/off, but it will get worse… till you get stranded.

That is often the electroplate failure. (Speed sensor on them dies).

post up the general area where you live and ask for recommendations for a nearby Independant MB Specialist. - you want one who has the full STAR diagnostics system.

STAR interrogates components to a deep level and can save money in the long term.

A good indie will get it fixed for a fraction of a dealer. (And usually take more care).

about 4 yrs ago my electroplate was around £500….

They were the same price last year!

 

[ajlsl600]

So built in speed sensor costs u 500 quid on my cats I think sensor about 130 an 5 min to change. D7 a bit of a buxxer. .

 

[00slk]

The D disappearing from the dashboard points to a selector module fault. Not inside the gearbox itself although a diagnostics session will need to be completed to confirm.

Been there done that

 

[Flyinspanner]

So built in speed sensor costs u 500 quid on my cats I think sensor about 130 an 5 min to change. D7 a bit of a buxxer. .

A speed sensor on a CAT? ….. think it’s a different type of sensor on an exhaust system.

D7 ? What’s that?

 

[Craiglxviii]

A speed sensor on a CAT? ….. think it’s a different type of sensor on an exhaust system.

D7 ? What’s that?

7th gear in drive I would imagine.

 

[ajlsl600]

A speed sensor on a CAT? ….. think it’s a different type of sensor on an exhaust system.

D7 ? What’s that?

D7 dozer, uses a nu of speed sensors... Gearbox electroplate/ exhaust system?

 

[Blobcat]

A speed sensor on a CAT? ….. think it’s a different type of sensor on an exhaust system.

D7 ? What’s that?

7th gear in drive I would imagine.

​

 

[ajlsl600]

Eureka. Only one here somewhat shabbier.

 

[Blobcat]

Eureka. Only one here somewhat shabbier.

 

[ajlsl600]

View attachment 80115

Mine is D7r but otherwise looks very similar, tatty.