Merc Vito 2013 auto I’m going round in circles with.

[Robbie260]

Hi all after quite a while now this is a long story have a customers automatic Vito that’s having issues with the auto box. I’ll start at the beginning.

It wasn’t coming out of park unless the emergency release was pressed, was staying in park on the dash was engaging reverse and reversing went into neutral, then would go into drive and be either stuck in first gear or not want to drive at all (it be trying too but not managing you could push the van and there be almost no weight too it but it wouldn’t manage to move forward under its own steam).

Plug in the diagnostics and it comes up with a C404 error code ( signal selector lever position) and P1856 ( selector lever position detection has failed).

Take the dash apart and removed the selector sensor module with ribbon attached the ribbon looked chaffed through and burnt at a point so assumed the ribbon had shorted on something and fried the circuit board. This part is no longer made by Mercedes but the owner managed to source a second hand one with matching codes.

It was installed and there was no change. Later I found a magnet off the bottom of the selector lever floating around inside the selector lever housing which had come adrift and I glued this back in place. Things improved slightly. The vehicle on the first try now comes out park and when you start reversing displays reverse on the dash with the new selector sensor module but will stay displaying reverse if you select neutral or drive and will still be stuck in first gear and when returned to park still displays reverse on the dash so unless the car is turned on and off again it won’t come out of park again without pushing the emergency release. With the old sensor module the original fault remains.

I have resistance tested the wiring and that all appears to check out.

I have sent the gearbox ECU and both selector sensor modules to ECU testing and they were returned saying they couldn’t test them.

The owner found a spare gearbox ECU on eBay with the same part numbers so we tried installing the originals and then taking a program copy of their details then programming in the new selector sensor module and ECU in that has made no difference.

Have even tried running a magnet over the sensor pickups myself unsure if this would work but thought it was worth a try and that doesn’t change the position displayed on the dash.

Anyone have any suggestions or encountered similar problem before?

 

[m_c]

I'd be looking at live data to see what was going on.

I've never really dealt with Vitos, but most modern autos, the gearbox ECU will signal to the dash what to display (probably via the SAM on a Merc), it's not simply a case of the dash reading where the lever is at.
So unless you have diag capable of viewing the live data in all the modules involved, there's not much you can do.

@Ubique may know more, as IIRC he has a bit experience with three pointed stars...

 

[Ubique]

I've not really any experience with the older stuff - but it does sound like the positional reference of the sensor and the correlation with the selector is out. TBH, I'd be looking for a replacement selector assembly as the position of the magnet will need to be millimetre perfect.

 

[Robbie260]

I'd be looking at live data to see what was going on.

I've never really dealt with Vitos, but most modern autos, the gearbox ECU will signal to the dash what to display (probably via the SAM on a Merc), it's not simply a case of the dash reading where the lever is at.
So unless you have diag capable of viewing the live data in all the modules involved, there's not much you can do.

@Ubique may know more, as IIRC he has a bit experience with three pointed stars...

Unfortunately the live data I can access doesn’t tell me much in regards to the selector lever.

I've not really any experience with the older stuff - but it does sound like the positional reference of the sensor and the correlation with the selector is out. TBH, I'd be looking for a replacement selector assembly as the position of the magnet will need to be millimetre perfect.

Right that dose make some sense but in other ways no sense. The magnet is obviously in a correct enough position to make one change to the position parameters on the dash if this was the case could I not reasonably expect the part to select between park and reverse continuously as the magnet is allowing this initial change as it recognises it’s in park again ounce the car is switch off and then back on.

 

[Keithmac]

You don't have to calibrate the selector position module do you?.

 

[Robbie260]

You don't have to calibrate the selector position module do you?.

According to Mercedes no you don’t and unfortunately I have never found a scan tool that offers that as a function so I’d assume not is the case.

 

[Ubique]

There's no calibration as it's built 'calibrated', your issue appears to be a mismatch between the selector and the transmission positions, as replacing the selector is not an option, I'd suggest finding some way of reading live values from both and comparing, the transmission should be the 'lead' position with the selector following it - it's the opposite way to what you'd think, but with a cable operated system, the electrical position has to report the physical position correctly. IIRC there is some adjustment at the transmission end, it might be worth moving a measured amount either way to see if that makes it better or worse.
Unfortunately the fix is only going to be some degree of 'bodge', unless you can get hold of a known-good selector assembly. I can't even send you WIS details as my login is passenger vehicles only and your VIN will be verboten to access....