Limp Mode Woes
 

My 97 c280 has about 122k. Several months ago it started occasionally going into limp mode after I'd applied hard brake pressure (not even slamming on the brakes, just a slightly harder-than-normal stop). Usually, if I turned the car off then back on after a couple of seconds it would reset.

THEN one day a couple of weeks ago, I braked not-that-hard and it started lurching between gears and the check engine light came on, but it was still shifting. I turned it off and about 30 minutes later drove it and the check engine light was still on, but it was shifting OK until it suddenly went back into limp mode. I gave it a couple of hours and tried again, but it stayed in limp.

I towed it to a mechanic who said it had stored and active codes for Transmission Turbine Sensors and Speed Sensors (he said these usually indicate transmission failure). He cleared the codes but said the MB has a design flaw in the transmission that causes the gears to slip out of place and I would have to get a new one (about $5k) to fix the problem.

The car has been running great since the codes were reset (one limp-mode incident, it reset itself), but HOLY COW! A new tranny at this mileage seems crazy. I really liked this mechanic, but haven't seen anything else about this design flaw anywhere.

Can anyone out there offer insight?

He was right about the early 722.6 tranies having a bunch of defects. One of those defects was a conductor plate with exposed circuitry that cause issues of speed sensor evaluation. It also contains the sensors which have issues of their own.

I would pull the pan and see if there is unusual debris in the pan. If it is clean I would replace the conductor plate.

thank you
 

thank you for your response. i'll give it a try.

I bought a 97 C230 sedan over two years ago with the same problem it would not shift to the higher gears. I had it checked it turned out the the rear speed sensors were bad, replaced them & reset the computer (via stardiagnose) all is well. (so far)

thank you, sd!