when driving in sport mode sometimes i'll manually downshift and noticed recently that the trans wouldn't hold the gear and shift right back up as if it was still in "d". so i pushed the mode selector button and it would only toggle between "s" and "c" mode with no option for "m"!

it will do this intermittently during every drive. any ideas?

 

Any codes? The trans will push a code to the trans module which then will send a error code to the primary ECU. Something is not right though.

Any leaks, fluid level, recent trans service? Common issue is a leaking electrical socket located on the trans. It can leak, then in no time send trans fluid straight up into the trans module located under the passenger footwell causing issues requiring removal and a thorough cleaning.

 

no codes. my 13 pin connector was replaced a while ago and isn't leaking and tcu connectors are dry.

 

sounds like a bad tcu or bad programming...

 

just an update and fyi. this was the result of a bad engine oil temp sensor. if the trans thinks the engine oil is too hot it will lock you out of manual mode.

 

no codes or messages of any sort?

 

very interesting! How did you find out the engine temp sensor was the problem. Is the oil temp sensor built into the oil level sensor?

 

LOL...x2. Good work!

 

He found out from the mac daddy of Benz mechanics. My buddy Ken! Friggin guy is a machine.

 

yep, as jim already knows, before i could even finish describing the symptoms to ken he was already giving me the answer!

 

Too bad I just saw this thread else I could have helped out as I went through this a year ago with a bad Oil level sensor(i'm assuming the same sensor unit measures the temp). Argued with the master tech for almost a week about this issue but he kept on giving me the "its supposed to work that way since its not a manual transmission...". The issue went away after I had them fix my oil level sensor because of random readings and messages. Eventually it made sense because the whole point seemed to be to keep the Engine RPMs low by using of the transmission. Mine would jump from M mode to sport D. Glad you got this resolved. Can be a scary thing when the car shifts gears and launches forward in traffic.

 

yeah, where the heck were you when i needed you! lol. i do find it amazing how little many techs know about amg's...or even worse what they "think" they know. it's nice to know there are at least a few good ones like ken and scott.