ML6.3 AMG – Hill Start problem – 58k miles. I originally posted my problem under a different title, but having identified the symptoms better and having had zero responses I am trying again with a much better and more accurate description of the issue.

The car will stop suddenly with the brakes being automatically applied after a hill start, when starting off gently at 1000 to 1200rpm. In either forwards or reverse. Starting off with gusto avoids the problem, but of little help when parked between cars on a hill.
Went into MB who were able to reproduce the effects on their multi car park ramps – information sent to MB technical for help – no relevant error codes. Subsequently MB Technical requested changing 4 wheel sensors, which one imagines would have raised error codes if any one of them was faulty, it looks as though a diagnosis has yet to be made.

Further testing since by me showed:-
1. If the hill start is not engaged, i.e. stopping by slowing down then holding it on the throttle (not using the brake pedal) and then starting off, there is no problem.
2. If the hill start is engaged and then the car is held on the throttle without creeping forward or even allowing it to slip backwards slightly to detect when the mechanism has disengaged, there is no problem when starting off. If during this test there is any forward motion before the mechanism disengages - the brakes jam on again.
This ties in with what the MB tech. found when he disconnected the hill start system. i.e. the problem did not occur.
3. Switching off the engine even for a few seconds resets the fault condition so that it is again easily demonstrated. i.e. I drove the car for 20 minutes and parked on a hill probably steeper than the multi-storey car park ramp at MB. A hill start test caused a mild brake application fault condition. Switching off the engine and on again whilst holding the car on the brakes caused the following test to show the fault as severe as when the car is cold.

This changes the characteristics of when the fault is observed: -
The previous supposition that the heat of the engine was important is probably false, instead it is probably how long the engine has been running which decides on how readily the fault can be demonstrated. The heat of the transmission fluid will be a factor on how steep the hill needs to be to show the fault at low revs, because when the fluid is hot it more easily drives the car forward (or backward) and the steeper hill is required to a gentle start in the required rev range of 1000 to 1200rpm.

It now looks as though the problem gradually diminishes the longer the engine has been running, but resets on a restart. Coupled with a required rev range 1000 to 1200rpm this makes me suspect failing capacitors as a potential cause. (my career was in electronics), but I am not familiar with the ML6.3 electrical set up.

Has anyone had a fault like this and what was done to solve it?

 

Just thought someone might like an update on this. MB apparently recognise the fault and confirm that fitting updated wheel sensors cures the problem. All four now fitted foc by MB and fault has cleared.