Auto box issue

[nixB10]

I'm currently driving a 2002 C270 auto. Its done approx 90K miles. Occasionally and for no apparent reason when driving it goes into neutral and it doesn't matter what I do with the gear lever it stays in neutral on the dash display ( and mechanically) until I stop and restart the engine. Its only happened a few times but is obviously worrying. Any ideas what might be causing this?

Edited by nixB10 on Sunday 24th June 16:47

[mbtech01]

to be 100% sure you need to have a diagnostic check done to see what stored faults are found in the etc (electronic transmission control module). At a guess i'd reckon that maybe the gearbox conductor plate is faulty. This is basically a printed circuit board that clips to the main valve body in the transmission & incorporates a speed sensor pickup. I've seen a few of these fail of recent causing various gearbox faults. Usually you'll see some sort of Y fault relating to a speed sensor fault come up. Its not a bad job to replace this conductor plate, you just need to drain the transmission oil, remove the transmission oil pan & filter then remove the valve body, remove the 6 solenoid valves then unclip remove/replace the conductor plate. The only problem you may have is you'll need to find a transmission oil master dipstick as the car does not have a dipstick to check the oil level.
As said this is just a thought & i hope you manage to get to the bottom of your problem.

[nixB10]

Thanks for that mbtech01. It had been suggested to me that the plate might be the issue. I'll follow your advice and get a diag check first and see what comes up.

[CarsOrBikes]

My guess would be the floor shift module if it the indicated gear on the dash isn't changing.

The immersed plate in the box is pretty common, and will often throw a speed signal problem but I don't know it would alter the displayed gear. Either may reset with key off/on

But... it needs going on diag

[mbtech01]

Good point about checking the floor shift & as said needs to go on diaagnostics. Have had another thought, it may be worth checking the ETC (electronic transmission control) module under the floor plate in the passenger front footwell area under the floor carpet. There's a possibility that it could be contaminated with transmission oil. If the elctrical plug that goes on the gearbox is leaking transmission oil gets sucked up by the wiring until it eventually makes it's way into the control module. This will then cause the electrical circuits to short causing gear shift problems, loss of drive etc. I've seen this a fair few times & it could be the cause of what you are experiencing. When the fault occurs its like rebooting your computer, you switch it of then back on again & it resets itself.
Its wort checking for peace of mind just to rule it out.

CarsOrBikes said:

My guess would be the floor shift module if it the indicated gear on the dash isn't changing.

The immersed plate in the box is pretty common, and will often throw a speed signal problem but I don't know it would alter the displayed gear. Either may reset with key off/on

But... it needs going on diag

[nixB10]

Thanks for the suggestions. I hoping to get the car booked in for a diag next week so I will see what that comes up with.