S Class 320CDI gearbox limphome mode

[Xtractorfan]

My 2001 S320CDI 130K mls has just gone into gearbox safety mode 2nd gear only, tried all manner of things, stop/restart, disconnect battery, all to no avail. I had the car put on a star diagnostic machine..the genuine merc equipment, tho not an MB stealership..but a recognised service centre.. The operator may not have been up to speed as it took 1&1/2 hrs to get a fix on the gearbox and a bit of prodding and half baked input from myself in an attempt to see how good this machine is.. anyhow the computer said yes two faults ... Now I know i should have taken note but basically the fault centered on intermittent and sporadic voltage to gearlever gizmos and lack of power at gearlever ... gearbox will not change to W mode and will not show or move in tip mode, any views would be most welcome.....:

 

[BlackC55]

It needs a new selector module by the sounds of it.

 

[Xtractorfan]

my one gear autobox

Further to my gearbox limp home problem oh and many thanks blackC55 for your reply..but it seems like I may have found the problem thanks to a merc breakers yard. I checked the autobox ecu and it was saturated in oil..common fault with this box apparently .. tho MB have never heard about it.. makes u wonder why they cant get these 'problem' motors running properly..must mention the breakers yard, Molloys, in Armagh N.Ireland tele no. 028 3756 8083
For the confused..like myself..the autobox ecu is located beside left hand bonnet hinge in a black fuse box type container.. it is the black cassete type box nearest the engine..(inside said box) lift out carefully and disconnect in upright position as the oil (if contaminated) will spill everywhere. Oh and a new one is only £700..so if ya dont know anything about electrics and how to clean it have a word with some of the computer / radio / tv guys who work with these things and always get a second opinion. and do not touch any of the internal components,, static from your person can blow small transistors and components to smithereens..and u try finding anything in smithereens..impossible

 

[television]

Oil will not harm an ECU it can be washed and a new harness fitted.

Oil is not conductive as shown on the test that I have done on a working skybox

 

[Xtractorfan]

My S320 CDI is now up and running perfectly after removing and cleaning the gearbox ECU I used kitchen roll to gently dab off the excess oil, then an airline to dispel any oil in awkward spots then a liberal coating of electrical contact/ switch cleaner allowing the ECU to drip dry I then used the same procedure on the loom contacts at both ends. The loom at the gearbox end was allowed to hang free overnight and drain ...amazing how much oil was in there ..new gearbox loom housing and seals fitted and car driven to local service dealer.. star machine but not MB dealer and hey presto pure smooth gear changes and car going like a dream. HEY ONE OTHER THING I have had the intermittent engine 3000 rev limit, over the past year, stop restart and everything ok again, tried everythng including MAFs 3 no.. two from motor factors (pierburg) and one from dealer (pierburg ) I kinda get the feeling my problem was stemming from low oil level in gearbox when i drained I only got about 3.5 ltrs out.. So if ur having problems its worth a check..but get it done properly better to give a dealer £20 rather than have to fork out for a new box..