1996 R129 500 SL Gearbox not changing gear.

[Stevenrcollinge]

Good morning all,

I have a 1996 R 129 500 SL that is stuck in its default second gear. Drive and reverse can be selected and it drives just fine other than it won’t change gear when driving. Does any know what this is and what I have to do to solve?

 

[wongl]

Sounds like your car is stuck in limp mode? Are there any warning lights in your car and is there a port for scanning error codes?

 

[Wearsthefoxhat]

Have you checked the atf level ?.


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[Stevenrcollinge]

Sounds like your car is stuck in limp mode? Are there any warning lights in your car and is there a port for scanning error codes?

Have you checked the atf level ?.


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Yes, all that is good.

 

[BTB 500]

Is this the 5-speed gearbox? Have you had the fault codes read on STAR? The 'electrical plate' is a pretty common failure, which will put the car into limp mode. This is a relatively cheap/easy repair though.

 

[grober]

The NAG automatic transmission set new standards when it was presented in 1995. This five-speed automatic transmission from Mercedes-Benz with electronic control and torque converter lock-up clutch offered unprecedentedly smooth and easy gear shifting. The light and comparatively compact transmission was initially introduced for the models fitted with V8 and V12 engines. From the summer of 1996 it became available for numerous classes of vehicle from the comprehensive passenger car programme.
Because your car is fitted with an electronic box its likely that in the absence of a fluid/ filter fault, the fault lies with the internal conductor plate or the seal on the plug that connects it the extenal electronic control unit- if it leaks fluid can migrate along the connection and mess up the electronics. Time to get the car to an autotransmission specialist familiar with these boxes. Other possibility is an electronics fault in the gear selector module

 

[Stevenrcollinge]

Is this the 5-speed gearbox? Have you had the fault codes read on STAR? The 'electrical plate' is a pretty common failure, which will put the car into limp mode. This is a relatively cheap/easy repair though.

I just don’t think it is in limp mode though. I can get up to 50mph which surely rules out limp mode. It just won’t go through the gears.?

 

[Stevenrcollinge]

The NAG automatic transmission set new standards when it was presented in 1995. This five-speed automatic transmission from Mercedes-Benz with electronic control and torque converter lock-up clutch offered unprecedentedly smooth and easy gear shifting. The light and comparatively compact transmission was initially introduced for the models fitted with V8 and V12 engines. From the summer of 1996 it became available for numerous classes of vehicle from the comprehensive passenger car programme.
Because your car is fitted with an electronic box its likely that in the absence of a fluid/ filter fault, the fault lies with the internal conductor plate or the seal on the plug that connects it the extenal electronic control unit- if it leaks fluid can migrate along the connection and mess up the electronics. Time to get the car to an autotransmission specialist familiar with these boxes. Other possibility is an electronics fault in the gear selector module

Thank you. I’m taking it into someone.

 

[BTB 500]

I just don’t think it is in limp mode though. I can get up to 50mph which surely rules out limp mode. It just won’t go through the gears.?

That's what limp mode on the gearbox does - it locks it into a single gear (2nd or 3rd ... I think it might vary depending on the engine) when you select D. There are no warning lights etc. (at least there weren't when it happened on mine).

 

[Stevenrcollinge]

That's what limp mode on the gearbox does - it locks it into a single gear (2nd or 3rd ... I think it might vary depending on the engine) when you select D. There are no warning lights etc. (at least there weren't when it happened on mine).

No warning lights at all. All the gear box filters and fluids have been changed too.

 

[grober]

Replacing Conductor Plate in 722.6 Autobox

 

[amazighman]

Change ATF , Filter , new conductor plate and hopefully will be good.

Another this to pay attention to is the Pilot bush plug on the side of the transmission can leak overtime lowering your fluid level.

Best is to get it Put on star diagnostic at a dealer or specialist .

 

[alabbasi]

Can happen when brake switch fails but will trip abs light and traction control (at least it did in my w210)
Else check TCM which I think is under the hood on those case and make sure it's not oily. If it is, the round plug seal has failed and is causing fluid to be pushed up the wires and onto the tcm
other likely causes are conductor plate

My suggestion is to change fluid, replace conductor plate and round plug while you're in there and give TCM a good clean. If your transmission tripped code, it would a speed sensor code. You'll need to reset the code with a scanner that can do the reset before your car will get out of limp mode.

Thanks