C63 Code U0101
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Junior Member
Joined: Sep 2017
Posts: 16
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C63
C63 Code U0101
I've got a 2009 W204 Mercedes C63
Mileage 83k
The car has thrown code U0101 and will intermittently go into limp mode, sticking in whichever gear is selected when the the issue takes place. I am unable to shift out of that gear. When this issue is present, there are harsh engagements between park, reverse and drive. Also, the car typically displays which gear is selected on the dash (Park, Reverse, Neutral, Drive). When this issue occurs, that display fails to show which gear is selected.
I've been able to occasionally clear the code, which puts the car back into normal operation until it's triggered again (within 10 to 15 minutes of normal driving). Once the code is clear, the harsh engagements between park, neutral and drive disappear and the car shifts normally.
I changed the battery about 6 weeks ago and let the car sit for a month fully charged. I had to boost the car twice after letting it sit, my first assumption was a bad battery. I've replaced the battery with another brand new one, although the previous new battery passed load tests (just wanted to absolutely rule out a faulty battery since that's what changed).
The alternator is showing normal charging voltage.
I've read that code relates to a loss of communication with the TCM. Reading the forum, some common causes are faulty wiring or a failed or failing conductor plate.
Where it's an intermittent issue that is temporarily resolved with clearing the code, it may be an electrical issue. The car was tuned at around 15k km with a eurocharged tune, not sure if that's relevant. I haven't noticed any issues since having it tuned. The car has not been driven hard what so ever so I don't believe this is a result of any abuse.
I've tried to get the car into the dealer but they're booking into middle November, gave me an excuse saying they have no techs able to work on older cars.
I've got evidence of mice under the hood, I'm going to try and trace all wiring from the transmission. While it's a long shot I've got several months before the dealer can touch it, frankly it sounded like they didn't want anything to do with the car.
Has anyone experienced this issue? Anyone know where I could find some wiring diagrams to get me started?
Thank you in advance. I've researched this extensively however I haven't been able to find anything overly useful.
Mileage 83k
The car has thrown code U0101 and will intermittently go into limp mode, sticking in whichever gear is selected when the the issue takes place. I am unable to shift out of that gear. When this issue is present, there are harsh engagements between park, reverse and drive. Also, the car typically displays which gear is selected on the dash (Park, Reverse, Neutral, Drive). When this issue occurs, that display fails to show which gear is selected.
I've been able to occasionally clear the code, which puts the car back into normal operation until it's triggered again (within 10 to 15 minutes of normal driving). Once the code is clear, the harsh engagements between park, neutral and drive disappear and the car shifts normally.
I changed the battery about 6 weeks ago and let the car sit for a month fully charged. I had to boost the car twice after letting it sit, my first assumption was a bad battery. I've replaced the battery with another brand new one, although the previous new battery passed load tests (just wanted to absolutely rule out a faulty battery since that's what changed).
The alternator is showing normal charging voltage.
I've read that code relates to a loss of communication with the TCM. Reading the forum, some common causes are faulty wiring or a failed or failing conductor plate.
Where it's an intermittent issue that is temporarily resolved with clearing the code, it may be an electrical issue. The car was tuned at around 15k km with a eurocharged tune, not sure if that's relevant. I haven't noticed any issues since having it tuned. The car has not been driven hard what so ever so I don't believe this is a result of any abuse.
I've tried to get the car into the dealer but they're booking into middle November, gave me an excuse saying they have no techs able to work on older cars.
I've got evidence of mice under the hood, I'm going to try and trace all wiring from the transmission. While it's a long shot I've got several months before the dealer can touch it, frankly it sounded like they didn't want anything to do with the car.
Has anyone experienced this issue? Anyone know where I could find some wiring diagrams to get me started?
Thank you in advance. I've researched this extensively however I haven't been able to find anything overly useful.
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Joined: Jul 2025
Posts: 10
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2009 Mercedes C63
I've got a 2009 W204 Mercedes C63
Mileage 83k
The car has thrown code U0101 and will intermittently go into limp mode, sticking in whichever gear is selected when the the issue takes place. I am unable to shift out of that gear. When this issue is present, there are harsh engagements between park, reverse and drive. Also, the car typically displays which gear is selected on the dash (Park, Reverse, Neutral, Drive). When this issue occurs, that display fails to show which gear is selected.
I've been able to occasionally clear the code, which puts the car back into normal operation until it's triggered again (within 10 to 15 minutes of normal driving). Once the code is clear, the harsh engagements between park, neutral and drive disappear and the car shifts normally.
I changed the battery about 6 weeks ago and let the car sit for a month fully charged. I had to boost the car twice after letting it sit, my first assumption was a bad battery. I've replaced the battery with another brand new one, although the previous new battery passed load tests (just wanted to absolutely rule out a faulty battery since that's what changed).
The alternator is showing normal charging voltage.
I've read that code relates to a loss of communication with the TCM. Reading the forum, some common causes are faulty wiring or a failed or failing conductor plate.
Where it's an intermittent issue that is temporarily resolved with clearing the code, it may be an electrical issue. The car was tuned at around 15k km with a eurocharged tune, not sure if that's relevant. I haven't noticed any issues since having it tuned. The car has not been driven hard what so ever so I don't believe this is a result of any abuse.
I've tried to get the car into the dealer but they're booking into middle November, gave me an excuse saying they have no techs able to work on older cars.
I've got evidence of mice under the hood, I'm going to try and trace all wiring from the transmission. While it's a long shot I've got several months before the dealer can touch it, frankly it sounded like they didn't want anything to do with the car.
Has anyone experienced this issue? Anyone know where I could find some wiring diagrams to get me started?
Thank you in advance. I've researched this extensively however I haven't been able to find anything overly useful.
Mileage 83k
The car has thrown code U0101 and will intermittently go into limp mode, sticking in whichever gear is selected when the the issue takes place. I am unable to shift out of that gear. When this issue is present, there are harsh engagements between park, reverse and drive. Also, the car typically displays which gear is selected on the dash (Park, Reverse, Neutral, Drive). When this issue occurs, that display fails to show which gear is selected.
I've been able to occasionally clear the code, which puts the car back into normal operation until it's triggered again (within 10 to 15 minutes of normal driving). Once the code is clear, the harsh engagements between park, neutral and drive disappear and the car shifts normally.
I changed the battery about 6 weeks ago and let the car sit for a month fully charged. I had to boost the car twice after letting it sit, my first assumption was a bad battery. I've replaced the battery with another brand new one, although the previous new battery passed load tests (just wanted to absolutely rule out a faulty battery since that's what changed).
The alternator is showing normal charging voltage.
I've read that code relates to a loss of communication with the TCM. Reading the forum, some common causes are faulty wiring or a failed or failing conductor plate.
Where it's an intermittent issue that is temporarily resolved with clearing the code, it may be an electrical issue. The car was tuned at around 15k km with a eurocharged tune, not sure if that's relevant. I haven't noticed any issues since having it tuned. The car has not been driven hard what so ever so I don't believe this is a result of any abuse.
I've tried to get the car into the dealer but they're booking into middle November, gave me an excuse saying they have no techs able to work on older cars.
I've got evidence of mice under the hood, I'm going to try and trace all wiring from the transmission. While it's a long shot I've got several months before the dealer can touch it, frankly it sounded like they didn't want anything to do with the car.
Has anyone experienced this issue? Anyone know where I could find some wiring diagrams to get me started?
Thank you in advance. I've researched this extensively however I haven't been able to find anything overly useful.
Thread Starter
Junior Member
Joined: Sep 2017
Posts: 16
Likes: 1
C63
I fixed it! Initially I figured it must be something on the conductor plate, speed sensor or a ribbon cable.
Once I was underneath the car, I noticed the wiring harness for the transmission (4 pin) was very loosely hanging in place. When I touched it, it fell out of the conductor plate socket.
The wiring connector locking tab had worn down, allowing the harness plug to slip off. I used a zip tie and some seizing wire to secure it in place. I considered different adhesives or silicone but none of them really play well with plastic. Plus there was a small film of oil on everything. So far so good, it completely fixed the problem. Once you're under the car, you just remove the two plastic skid plates and there's a small metal cover that is supposed to protect the harness plug. Very simple job, that's where I'd start if I were you.
Good luck.
Once I was underneath the car, I noticed the wiring harness for the transmission (4 pin) was very loosely hanging in place. When I touched it, it fell out of the conductor plate socket.
The wiring connector locking tab had worn down, allowing the harness plug to slip off. I used a zip tie and some seizing wire to secure it in place. I considered different adhesives or silicone but none of them really play well with plastic. Plus there was a small film of oil on everything. So far so good, it completely fixed the problem. Once you're under the car, you just remove the two plastic skid plates and there's a small metal cover that is supposed to protect the harness plug. Very simple job, that's where I'd start if I were you.
Good luck.
