W140 722.6 gearbox trouble (see video)

[MrT8064]

A couple of weeks ago I bought myself a tired but well maintained W140 S320. I hadn't driven an S-class before, but can safely say it is by far the most comfortable and relaxing car I have been in. Simply incredible.

I promptly set off to Europe for a road trip, but 700 miles in the gearbox went into limp mode (limiting us to 2nd gear, reverse and park). I took it to Mercedes in Germany which was fortunately very close to where the problem emerged.

They immediately plugged it in to their diagnostics machine (kindly free of charge), and pulled the following couple of codes:

10 - 106 - P0702 - Solenoid Supply Voltage Out Of Range
11 - 107 - P0715 - N2 - N3 Sensor Supply Voltage Out Of Range

We were told that the car would require new electronic gearbox internals(?!), which would cost €880 euros plus €500 labour. So we made the decision to limp the car home. 250 miles at 20mph later and we arrived in Folkestone and got a tow home up the motorway.

I took to the internet and realised that it was probably only the conductor plate in the gearbox which needed to be replaced, however I would really appreciate anyone's opinion on this. I know nothing about these 722.6 boxes!

When I was underneath the car this morning - I saw that the shifter linkage bush (I think it is called) was totally missing. I have made a video of this for reference below. It occurred to me that perhaps this was causing the gearbox to create false error codes - however I have found nothing on the internet about this to confirm my suspicions. Does anyone know whether my theory is plausible?

Thanks!

https://www.youtube.com/watch?v=fOM88bOydqw

 

[bogcaster]

I changed my 722.6 conductor plate myself a few years ago, but that only cost me a few hundred pounds for the plate, pilot bushing, new atf and filter using genuine parts. It could be the electronic control module too but mine was done under warranty by the dealership a few years earlier too that during a service - that didn't take long. If I recall, that was external to the gearbox within the passenger compartment somewhere near the selector. After my conductor plate change (half a day but being very meticulous) I had to get the gearbox reset at my local gearbox specialist to get it out of the 2nd gear limp mode.

Check out the well documented Pilot Bushing (not selector bushing but where the wires plug into the gearbox) leaking problem which causes atf to capillary action its way up to the gearbox electronic control unit through the wires, ultimately trashing it and needing replacement.

Missing selector bushing needs sorting but unlikely to cause your problems in my opinion.

 

[bogcaster]

I should add that someone on this forum who understands the codes will be able to confirm what needs replacing before spending money on the wrong parts.

 

[ivandraganov]

So we made the decision to limp the car home. 250 miles at 20mph later and we arrived in Folkestone and got a tow home up the motorway. [/URL]

You never did that,its simlpy bonkers...

 

[Borys]

On my last w140 limp mode was caused by low transmission fluid
Those boxes are bulletproof
Newer 7g cause problems but 5 speeds - can detonate a bomb inside and they will still run
As said investigate more before spending money, fault codes can be misleading sometimes

 

[ChrisA]

I had similar and changed the conductor plate at local MB Stealer......all good for 6000 miles. I then decided to upgrade the transmission with built parts due to increase in power mods.

Get it to your local Indie who can put your car on Star and take it from there

 

[MrT8064]

Thanks for the replies so far.

There doesn't appear to be an oil leak around the plug on the gearbox - but I guess this will be worth replacing if I do end up having to do the connector plate.

When MB Germany diagnosed the car, they also checked the transmission fluid and said 'It is low, but not too low' - perhaps this would be worth topping up first!

And yes - we really did drive the car back to the UK in second gear. We bought a good map and only picked the tiniest roads. The only point at which we had to go on a motorway/dual carriage way was 200m before the Eurotunnel entrance. No problem as the car can do over 50mph, all be it at 5,500 rpm!

Does anyone have advice on the fault codes I have listed above? I am really keen to avoid taking the car to get rediagnosed in the UK if possible.

Many thanks again.

 

[MrT8064]

I just had a look at the transmission control module under the bonnet.

There was a bit of oil around the plugs - not a good sign!

I took the TCM out of it's casing and there were a few drops of oil on the circuitry. It looked like it had been opened up several years ago too (a few old looking scratches on the plastic).

I guess this could be my problem - I'll check the plug under the car next and report back!

 

[MrT8064]

I have just been under the car to check the transmission plug.

There was a tiny bit of oil on it, but nothing like some of the pictures I have seen of really bad ones.

Here is a picture of the TCM - I have circled where the oil is, and where the corrosion is.

Do you think this is likely to be the cause of my problems? Or a red herring?!

Thanks!

 

[MrT8064]

Just to update for anyone stumbling across this thread:

I bought a cheap Carsoft 7.4 scanner, and after cleaning the transmission control module, tried resetting the codes... It worked!

A week later, and over 300 miles down everything is going well!