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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Mercedes Benz Qualified Diagnostic Technician
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car sometimes will not changegear

Customer Question

car sometimes will not changegear
Submitted: 3 years ago.
Category: Mercedes
Expert:  MB Paul replied 3 years ago.

Hi,


The transmission being stuck in 1 gear is an indication that it has gone into limp mode.


If the transmission is going into limp mode then it should have stored a fault code - the first thing to do is get the codes read on a diagnostic tool.


Also the oil level should be checked - there is no dipstick installed from the factory so a special tool is required (a dipstick! These are available from tool suppliers or also on ebay).


Check the transmission for oil leaks - this transmission is prone to leaking from the electrical connector on the front of the transmission . If leaking from here then the electrical spacer & seals in the transmission will need to be replaced & the electrical connector cleaned with electrical cleaner.


A common fault inside the transmission is with the electrical plate - this usually shows up as a code for the transmission speed sensors. The valve chest needs to be removed for this.


Another possibility can be undervoltage fault codes stored – this is often down to a faulty battery. The battery should be checked with an electronic battery tester if undervoltage fault codes are present in the transmission ECU.


I would also recommend a transmission oil & filter change & inspect inside the sump pan for any signs of swarf indicating internal wear or damage to the transmission .



Best regards, Paul

MB Paul and other Mercedes Specialists are ready to help you
Customer: replied 3 years ago.

I believe that .there is a filter in the box could this be the fault ! also there is a plus & minus mark near gearlever could you tell me what this is for!

Expert:  MB Paul replied 3 years ago.
Hi,

The filter is not usually the cause - it is usually due to electrical issues. If repairs are being carried out to the transmission then it is usually a good idea to change the oil & filter at the same time.

The + & - is for the manual tiptronic function - pushing the gearshift towards the - shifts down a gear & towards the + shifts up.

In all honesty the box responds much better in auto mode & under normal conditions is best left to shift itself in my opinion!

Regards, Paul