MattiasPoul

Did a bit of searching around this forum and found a lot of different proposals for fixing my issue. I'm not doing the work myself, but want to have a better understanding of what's going on, would like good advice for what to do next..

Car: 2005 SL55
Transmission no: 2302700700 - 722.643 0 - 5433032
Error code: P220A (comparasion of revs not possible - ish)

Problem is, driving (especially pushing the gearbox) it suddently lock in 2nd gear and refuse to change. Have also experienced it just selecting neutral even though display still shows "S". When problem occurs, I'm not able to select between Sport, Comfort, Manual - neither does it react pulling the leaver to "N" and back to "D" - unless i park, then it selects 2nd gear. Turning car off and turning on again removes problem.

What we've done:
1) Cleaned the plug to the ECU (behind glovebox), was a little wet from some low density oily fluid?
2) Cleaned the plug to the gear box, big plug with like 9-12 plugs in it.. Very oily, but guess that's normal since it's inside the gearbox?

Possible solutions from forum:
1) Replace conductor plate
2) Check oil fluid (had it changed 5000 miles ago, never had any problems, and seems no leaking of gear oil, so maybe unlikely?)
3) Replace transmission.
4) Other?

Any thoughts that might help me decide what to do next?

latemodel21

You need to begin by replacing your Plug adapter (also called "pilot bushing" by MBZ pn A2035400253). this is the seal between the harness exiting the transmission and the conductor plate. This is not your whole problem, but since you found oil at the TCU, this part has clearly failed. When this part fails, the fluid actually wicks up the interior of the wires to the TCU. Opinions vary as to whether ATF in the TCU is fatal. Some folks have drained out the fluid (in the TCU), replaced the seal (adapter plug) and have no further problems. I suspect (based on the symptoms you are finding) that you may end up having a damaged TCU.

I would definitely try solving the problem in this order.

1)replace plug adapter and clean fluid out of TCU (contact cleaner should be fine) and retest

note: there is no simple way to remove fluid from harness, but if you cut off the source (by replacing seal at transmission) it should no longer be forced into the TCU. I would also suggest that you rotate the TCU in it's mount (-90°) so that it is pointing down so if your seal fails again (or if you are concerned about residual fluid in the wires) nothing further will make it past the connector of the TCU

(below are a few pics of the TCU remounted)


if problem persists,


2) swap in known good TCU and retest





hope that helps,
Chris

MattiasPoul

Hi Chris

Replaced plug adapter, cleaned TCU (also the print card itself had a tiny bit of oil on it) and hope problem is solved. If not, will try to replace TCU.

Thank you very much for your help, now I just gotta do some test driving

Edit: By the way, had the tester connected to the car again today. Got two new error codes I haven't seen before (these are created before cleaning TCU and before exchanging plug adapter).
P2500, P2069

cal1

I hope you have the problem solved. If not, check this out. It is good viewing for anyone with a tranny like ours.


I watched all 6 parts one Saturday morning.

MattiasPoul

Problem is not yet solved, I was able to reproduce "lock in 2nd gear" problem earlier. MB workshop said it might be a better idea to start changing some electric printed circuit inside the gearbox, unfortunately didn't get the part no but we'll try that monday morning.

He strongly refused the TCU could cause this problem, so I wonder.... Anyway, this other fix is cheaper (they charge 1500US$ for a new ECU including taxes here in Denmark..) so we'll go with the cheaper option first I believe.

Will watch the videos later, thanks for that recommendation.

latemodel21

Your mechanic is referring to the conductor plate ...

the TCU 0345451032 is $750 new (oediscountparts.com) and closer to 100 used ... to be clear, when I said "swap in" I meant swap in a known good one .... not necessarily buy it ... of course sometimes you don't get a choice .

the conductor plate should be close to $150 new ... and seems like a reasonable thing to replace

Chris

MattiasPoul

Conductor plate (mb part no A1402701161 sure seems to have been my problem. Had no problems for 500 miles now.

Thanks a lot everyone! Especially the videos were really helpful.

cal1

It sounds like your problem is solved. Glad to hear it. I will be doing a tranny fluid change this fall before putting my SL to bed for the winter. I am seriously considering replacing the conductor plate and plug while I have the pan off.

MattiasPoul

Local dealer actually said when I bought the spare part, that whenever they service this gearbox they always recommend to change the conducter plate "while we're in there anyway". Have driven enough miles since to say this problem is completely solved. I'm definitely one happy SL55 owner

cal1

When these bad boys are running well they are absolutely sublime.