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Hey guys! My 2007 6hp26 transmission was working fine, but before it broke down, I got two error codes (p0720 and p0741), but nothing changed. Suddenly, the transmission just stopped moving forward and backward. When I turn it off and start it again, it continues to work until the first stop.
The oil level is fine, there was one pin in the sand on the transmission.
I removed the pan, everything is clean there, there is nothing even on the magnets. I removed the hydraulic unit, the rubber seals are intact.
When the car is work, you can hear a ringing sound in the area of the torque converter.
I wonder if the TCM firmware has crashed? Or has the TCM itself died?
Last edited by psix; Nov 11, 2025 at 09:32 AM.
Reason: Added Translation
Here are the definitions and published possible causes of the Diagnostic Trouble Codes you have listed:
When I see so many different DTCs that could be related to communication with the Mechatronic/Transmission Control Module, my first suspect is fluid contamination of the transmission electrical connector. This occurs because the rubber O-rings on the connector sleeve harden and contract with age, allowing transmission fluid to leak into the connector and to insulate the connector pins, causing a loss of communication with one or more components inside the transmission.
The connector is high on the rear end of the transmission and can be a little difficult to access. There is a locking ring or collar with two tabs that must be rotated counter-clockwise until it releases from the connector sleeve. The harness connector can then be withdrawn from the connector sleeve. With a bright light and an inspection mirror, check for evidence of fluid in the connector. If you find any fluid, the sleeve must be replaced. To replace the sleeve, the pan must be removed again for access to the sleeve locking handle.
Regarding the valve body seals, they tend to harden and compress, causing a loss of pressure between the transmission and valve body, so just because the seals are intact does not mean they are still sealing properly. It would be prudent to replace them when you are changing the connector sleeve.
Let us know what you find and we'll be happy to help.
Hey! Thank you! The connector was dry, without oil, only one contact was in sand, I cleaned it, it did not help. I haven't put it back together yet; the hydraulic unit and TCM are in the trunk. I'm wondering what to do next. I could buy the entire transmission, but it's not convenient to change it on the ground.)))
Hey! Thank you! The connector was dry, without oil, only one contact was in sand,
I'm sorry that I do not understand "...in the sand." Can you please explain?
There have been reports of broken foil conductor traces in the Mechatronic circuitry inside the transmission.
Is it possible that a rodent has chewed some wiring between the transmission and other modules?
Have you checked for water in the compartment under the cabin air filter housing around the ECM electrical connector? I would expect more DTCs besides just the transmission-related ones, but it's worth checking.
Yes, you're absolutely right. I recently poured water from a Vendor on my windshield to check if water was getting into the sixth cylinder (it used to flood before).
It might have gotten into the connector, or it might be a coincidence, but it's worth checking.
one contact on the gearbox connector was a little dirty(in the sand)
Of course, it's unlikely that the problem is electrical, but it's worth checking. Moreover, I read that sometimes, due to problems with the TCM, the car wouldn't go forward or backward on 6hp26.
Of course, it's unlikely that the problem is electrical, but it's worth checking.
All of the DTCs you have could be caused by electrical issues. The first three codes in the definitions below indicate a problem with the ECM torque signal. This signal originates with the Mass Air Flow Sensor, but is communicated to the Mechatronic/TCM by way of the ECM. So another reason to check the ECM electrical connector for water ingress.
The P0741 could be due to a problem with the electrical circuit to the TC clutch pressure regulator solenoid. If the solenoid is not being electrically controlled properly, it cannot regulate the hydraulic pressure to the torque converter clutch.
The definition of P0720 is Output speed sensor circuit failure, which suggests an electrical problem.
Mechanical problems are not unheard of, but electrical problems are more common.
Don,Thank you very much!
I'll definitely check the wiring today. I'll have to put the torque converter back in, fill it with oil, and check everything.
I don't think so because of the solenoid.Sometimes the blade between the flywheel and torque converter in a BMW breaks, making this noise. Could the flywheel be broken, or something between the torque converter and the flywheel?
In any case, the transmission needs to be removed and then it will be visible. I put the valve body and oil pan back in place. Now I need to buy a plug for the oil pan (I broke the old one) and add oil. I'll check if it works.
I couldn't remove the connector under the cowl; a 10 mm bolt had turned in it.
I don't think so because of the solenoid.Sometimes the blade between the flywheel and torque converter in a BMW breaks, making this noise. Could the flywheel be broken, or something between the torque converter and the flywheel?
In any case, the transmission needs to be removed and then it will be visible. I put the valve body and oil pan back in place. Now I need to buy a plug for the oil pan (I broke the old one) and add oil. I'll check if it works.
I couldn't remove the connector under the cowl; a 10 mm bolt had turned in it.
Do you mean the screw on the electrical connector at the ECM? I'm not sure on the X200, but it may require a 5-lobe security Torx bit.
Don,Hey!)
Basically, I'm all covered in oil, I put everything back together.When the gear is engaged, this rustling noise appears in the area of the torque converter(like in the video)You drive back a little and forward, the gbf lights up and the car doesn't move,and the rustling disappears when the car is not moving.Erase the errors, and the car immediately starts moving again, a little bit before the gbf.The errors are different now P0736 P0730, and maybe I should try updating the TCM unit and checking the connectors under the hood? I think it will maybe make things.
Don,Hey!)
Basically, I'm all covered in oil, I put everything back together.When the gear is engaged, this rustling noise appears in the area of the torque converter(like in the video)You drive back a little and forward, the gbf lights up and the car doesn't move,and the rustling disappears when the car is not moving.Erase the errors, and the car immediately starts moving again, a little bit before the gbf.The errors are different now P0736 P0730, and maybe I should try updating the TCM unit and checking the connectors under the hood? I think it will maybe make things.
I'm wondering if you may have both electrical and hydro-mechanical faults. It would certainly be worth trying to rule out all electrical faults before diving into the mechanicals.
Hi, brother! I found a cheap transmission with a torque converter and replaced it. The car runs fine now. I was lucky with the transmission; it has 90,000 miles on it around Britain.
Of course, I'm curious what happened to the old gearbox,maybe I'll take it apart later. I don't know how to check the torque converter.
Doesn't go P0730 P0731 P0735
