2 day ago 2009 Mercedes Benz gl450 dashboard warning lights came on as "Drive to workshop without changing gear." I disconnected the negative terminal on the battery, now the sign has disappeared. The engine turns on and transmission goes on all gears. I don't know what is going on, Do you have any Ideas.

 

moved to X164 forum...
best to scan for codes first...

 

When that happened to my GL, it was the turbine speed sensor in the transmission. As I recall, it was an expensive repair that was covered under warranty.

 

Very likely the fault, but you'll have to read out the car on a bidirectional tool or MB star system to confirm. I

Brace yourself, it'll be about $3-4000 at the dealer or $169 for the part plus $400 for third party coding and $5-600 in labor at an indy.

 

When was the last time the trans was serviced?
It's worth servicing NOW if it's been more than 40,000 miles since last time.
You may get away with this if it is the Vehicle Speed sensor on the valve body. The contactor plates in the assembly lose connectivity due to accumulated dirt and grit and throw this code.
If left unchecked the VSS then short circuits and youll need a new part, and that part coded to the car's VIN.

 

In most if not all transmissions, the valve body is an analog mechanical computer in an oil bath shared with wet clutches. As the wet clutches wear, and shear the oil, contaminants float around and plug things up. The very kindest thing you can do to an automatic transmission is change the fluid and filter regularly, every 30K miles. It is cheap prevention. The clutches will still wear, but if you drive gently, the transmission can easily last 150K miles.

It is generally recommended to do a simple fluid and filter change, rather than a full flush, because the latter can excessively dislodge clutch wear material. It is better to do such rehabilitation on a neglected transmission gradually.

 

Looking at the error message you are getting, to me it sounds like the ISM, (Intelligent Servo Module), which works between the tranny and the TCM, its attached to the transmission and has easy-ish access, you might need a new unit and programmed to the car.
I personally would not go to stealership route, a reputable indy on the MB brand would be your best bet.
Yes if the fluid hasn`t been changed for a long time, do it, it would not hurt.

 

I agree with the fluid/filter change and no flush. It's something that should be done anyway and could be a relatively inexpensive (compared to other suggestions) fix.

There are three very highly rated shops near me that are dedicated to high end luxury cars (of which Mercedes is the "Chevy" of the group) and all recommended against flushing. And these aren't the sort of shops that look to save anyone money.

 

https://www.youcanic.com/mercedes-be...ging-gear-ism/

 

That’s a really good site with a thorough explanation of what is very likely going on here.

Still, service tranny, if it hasn’t been.
Codes will tell you what’s going on, hopefully A80 related as it is much less invasive than an VSS failure.