98 S420 transmission
 

My S420 does not shift from 2nd gear, I changed transmission but the problem is stilll there do you think it might be the TCU ( transmission control unit)?

First try to have the codes cleared from the ETC. You need to see a dealer or indie who has the right scanner. That is mostly the problem.

Well, I thank you very much sir for the info I would put action to it.

Since you installed a different transmission, try to follow what MB DOC has posted about re-adaptation, once the codes are cleared in the ETC.

Basically you accelerate gently through all gears without going over 1800 rpm, then coasts to a stop. Repeat 3 more times. Finally let it idle for at least 10 minutes.

So tell me, were you a novice like me, an "indie" or did you once work for them, this car was taken to aamco to repair the tranny, then put back into the car same prob, swapped it with another and this is where I am, however I dont think they followed the procedures you explained, just a hunch. thanks again.

When your old transmission had problem, your transmission control unit (ETC or TCU) went into limp mode (2nd and reverse only). As long as the codes are in the ETC, it shuts off power to the solenoids inside the transmission.

When you replaced with a different transmission, the codes in the ETC are still there so there is still no power to the replaced transmission.

An OBD II scanner cannot clear the codes in ETC. It seems the aamco folks are a bit challenged in this situation.

That does not mean the transmission they put does not have problem or your ETC isn't bad but you need to have the codes cleared before anything can happen.

You have me convinced, it all makes sense to me accordingly. Thanks again!

I would think aamco should have scanners that can clear the codes. It does require either Mercedes system, Snap-on, or others like Carsoft interfaces.

If they tell you they cleared P0xxx codes, then that is not good enough. The codes they need to clear are three digits such as 012, etc.

If you search for conductor plate, you should find many answers. Your original transmission might have that part failed. The part has received 3 - 4 updates.

I'll try to find out I don't remember them telling me if they did such a thing (not saying that they didn't) its been a while since they've worked on it, I am imagining that they all might have some common procedure they practice on each car depending on the manufacturer. I'm thinking this way because two transmissions had the same sypmtoms, what are the odds?