TCU help needed!
Thread Starter
Junior Member
Joined: Dec 2013
Posts: 22
Likes: 2
2012 E550 Sport Coupe, Capri Blue w/Almond Leather; 2005 Lexus IS300; 1983 Mercedes Benz 380SL
TCU help needed!
First the good news: the previous owners of my 2009 C350 Sport were apparently little old ladies who only went to church on Sundays and to the market on Mondays and bridge night on Fridays. The car had 29,000 miles on it when I got it last month and could pass for showroom new.
Now the bad news: these easy-driving owners also trained the transmission control unit to shift WAY too early!
Leaving my house and going down the street the car shifts into 3rd gear at 19 mph - and that's in sport mode! I have to absolutely floor the pedal to get it to wind out to near where it should be shifting in mild acceleration.
The salesman said it would take 1,000 to 5,000 miles for the TCU to re-learn my driving preferences. Yikes! I don't want to wait that long, put extra stress on the tranny by flooring it all the time, or burn up that much gas.
Does anyone know if the Mercedes dealer can reload the stock TCU software so I can teach it from scratch and not have to spend months over-writing the previous drivers' habits?
I read somewhere that you can get a TCU re-map for $800, but I don't want a street racer or to spend the money; I just want the car to shift sportily in sport mode.
Thanks in advance for any help.
Now the bad news: these easy-driving owners also trained the transmission control unit to shift WAY too early!
Leaving my house and going down the street the car shifts into 3rd gear at 19 mph - and that's in sport mode! I have to absolutely floor the pedal to get it to wind out to near where it should be shifting in mild acceleration.
The salesman said it would take 1,000 to 5,000 miles for the TCU to re-learn my driving preferences. Yikes! I don't want to wait that long, put extra stress on the tranny by flooring it all the time, or burn up that much gas.
Does anyone know if the Mercedes dealer can reload the stock TCU software so I can teach it from scratch and not have to spend months over-writing the previous drivers' habits?
I read somewhere that you can get a TCU re-map for $800, but I don't want a street racer or to spend the money; I just want the car to shift sportily in sport mode.
Thanks in advance for any help.
Newbie
Joined: Oct 2013
Posts: 10
Likes: 0
From: Fresno, California
2010 Mercedes C300 Sport, 2005 BMW 645ci, 2013 Hyundai Veloster Turbo, 1998 Porsche 911 Turbo
You could try to "reset" the TCU. There are many post on how to do it, i dont remember how to at the moment 
I know it is really easy tho, take about 3minutes of your time. It worked for mine and i bought my car used too.
I know it is really easy tho, take about 3minutes of your time. It worked for mine and i bought my car used too.
Senior Member
Joined: Mar 2011
Posts: 377
Likes: 0
From: Orange County
'10 C300
Courtesy of user Cpbball3
(0.) Get into the driver's seat, and make sure all doors, windows, and sunroof is closed.
(1.) Turn the ignition key to the on (not start) position. <== Position #2 where all the lights on the dash turn on but NOT to where the engine turns on!
(2.) Press the gas pedal to the floor and hold for five seconds.
(3.) Turn the key to the "off" position (don't remove the key), then release the gas pedal. <== I personally keep the gas pedal depressed for 5-10 additional seconds AFTER I turn off the key.
(4.) Wait at least two minutes for TCU to reset. (key in) <== Very important to leave the key in the ignition!
(0.) Get into the driver's seat, and make sure all doors, windows, and sunroof is closed.
(1.) Turn the ignition key to the on (not start) position. <== Position #2 where all the lights on the dash turn on but NOT to where the engine turns on!
(2.) Press the gas pedal to the floor and hold for five seconds.
(3.) Turn the key to the "off" position (don't remove the key), then release the gas pedal. <== I personally keep the gas pedal depressed for 5-10 additional seconds AFTER I turn off the key.
(4.) Wait at least two minutes for TCU to reset. (key in) <== Very important to leave the key in the ignition!
Junior Member
Joined: Dec 2013
Posts: 32
Likes: 2
2022 EQS 450+ until my 580 comes in
Courtesy of user Cpbball3
(0.) Get into the driver's seat, and make sure all doors, windows, and sunroof is closed.
(1.) Turn the ignition key to the on (not start) position. <== Position #2 where all the lights on the dash turn on but NOT to where the engine turns on!
(2.) Press the gas pedal to the floor and hold for five seconds.
(3.) Turn the key to the "off" position (don't remove the key), then release the gas pedal. <== I personally keep the gas pedal depressed for 5-10 additional seconds AFTER I turn off the key.
(4.) Wait at least two minutes for TCU to reset. (key in) <== Very important to leave the key in the ignition!
(0.) Get into the driver's seat, and make sure all doors, windows, and sunroof is closed.
(1.) Turn the ignition key to the on (not start) position. <== Position #2 where all the lights on the dash turn on but NOT to where the engine turns on!
(2.) Press the gas pedal to the floor and hold for five seconds.
(3.) Turn the key to the "off" position (don't remove the key), then release the gas pedal. <== I personally keep the gas pedal depressed for 5-10 additional seconds AFTER I turn off the key.
(4.) Wait at least two minutes for TCU to reset. (key in) <== Very important to leave the key in the ignition!
Thread Starter
Junior Member
Joined: Dec 2013
Posts: 22
Likes: 2
2012 E550 Sport Coupe, Capri Blue w/Almond Leather; 2005 Lexus IS300; 1983 Mercedes Benz 380SL
All OK now
I went to the dealer and asked the service dept to reset the TCU to factory. They did it for free, and I followed other advice on the forum to drive the first 40-50 shifts as i want it to shift. Did that both in "C" and "S" (they have separate memories).
With the ECU re-mapping and TCU reset the car is a joy to drive now.
Thanks all!
With the ECU re-mapping and TCU reset the car is a joy to drive now.
Thanks all!
