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From my reading it seems to be the electric conductor plate / transmission valve control module on the transmission valve body. However, I'm inclined to believe that this may not be the case for my car due to the circumstances of how I started getting this problem with my car (read below).
History
------------------
My car's rear left muffler fell off (don't ask, the mechanic who owned the car before me cut them off and re-welded them), made a big noise, broke my taillight, and unhinged the bumper.
I drove home after with no limp home problem or stuck 3rd gear transmission. The next day, the car started the limp mode home problem and has been doing it ever since. The car memory seems to forget it has problems shifting when you turn off the engine because the car drives and shifts fine for the first 5 minutes then reverts back to limp home.
Things I've Done
-----------------
Transmission Plug and Wire Harness
I've checked the transmission wire harness and the plug that goes into the transmission, took it out, cleaned it with a pressurized air hose and sprayed brake fluid in it. There was no visible leaking from the plug or into the wire harness. Afterwards, I drove the car from the shop and it drove fine and switched gears - I even manually switched them.
The next day the problem re-appeared.
ABS Speed Sensors
I checked the rear left and rear right ABS speed sensors with my dad and mechanic (vehicle/wheel speed sensor), tracing the wire to and from the connecting behind the wheel hub all the way into the connecting into the car body. The mechanic said it "looked" fine. Note that the rear right ABS speed sensor was brand new (still looks shiny black) and had been replaced earlier this year. Also the rear left ABS speed sensor would also be on the same side as where the muffler broke off.
Question / Conclusion
Can anyone give me some guidance to support my theory that it is ABS speed sensor related - I don't want to go aimlessly swapping them out. I am inclined to believe this to be true due to the circumstances of when the error started appearing.
Some other troubleshooting details:
- did a complete transmission flush earlier this year
- my car has had ABS/EPS/Check Brakes errors for the past year and half and never had this problem
Full list of the car repairs I've done since I've owned this car (1.5 years) in attached image:
Hey bro, there is no free lunch---the OBD 720 fault simply tells the owner there is a fault in the TCU-----you need factory or equal software to read the TCU.
Once you do that you will have the specific reason for the 720 fault and able to fix or sell the car------all else is pure speculation and the Ben's Wurld crew will jump on this post and start giving you all sorts of wild speculation and misinformation---be watchful, especially PJ!!
Think about it. How more specific can be "output speed sensor" ?
The 5-speed transmission has huge wealth of information posted on forum where Plutoe was banned for his stupid remarks.
Think about it. How more specific can be "output speed sensor" ?
The 5-speed transmission has huge wealth of information posted on forum where Plutoe was banned for his stupid remarks.
Correct however if I remember correctly the sensor wire is routed right next to the muffler assembly. I think that wire is damaged.
Hey bro, there is no free lunch---the OBD 720 fault simply tells the owner there is a fault in the TCU-----you need factory or equal software to read the TCU.
Once you do that you will have the specific reason for the 720 fault and able to fix or sell the car------all else is pure speculation and the Ben's Wurld crew will jump on this post and start giving you all sorts of wild speculation and misinformation---be watchful, especially PJ!!
Hmm, was hoping that I could avoid that. I have setup an appointment with a local indy shop that specializes in Euro imports for this Saturday. They have a high positive reviews online and I've seen their shop before on the outside, they look professional.
Originally Posted by Plutoe
Once you do that you will have the specific reason for the 720 fault and able to fix or sell the car
haha yes, pass the misery / hot potato to some other poor fella. It's mine now and I will be driving it til the rust finishes it off. I've "invested" too much cash into this one, it's pretty much got nothing left that can break or go faulty.
Correct however if I remember correctly the sensor wire is routed right next to the muffler assembly. I think that wire is damaged.
--Kyle
Hey Kyle,
This sounds promising - which sensor wire are you referring to specifically, the ABS one? I will have someone take a closer look into that but need a bit more detail (so I know where to look too )
As I said, there is HUGE wealth of informations about those transmission on the net already, so no reason to break open door.
Don't wont to open another endless topic about the same thing, but the tip would be that even the code points to speed sensor, it doesn't have to be bad sensor itself.
Other possibility is shorted sensor wiring aka contamination at pilot bushing, or TCM.
No guarantee it will work in this case, but hundreds of owners fixed those errors with $40 worth of materials and 1 hr of work.
Some did it even without ramps or stands. High curb works too for this assignment.
As I said, there is HUGE wealth of informations about those transmission on the net already, so no reason to break open door.
Don't wont to open another endless topic about the same thing, but the tip would be that even the code points to speed sensor, it doesn't have to be bad sensor itself.
Other possibility is shorted sensor wiring aka contamination at pilot bushing, or TCM.
Good points, the electronic connector / pilot bushing that plugs into the transmission was not leaking or full of fluid when I pulled it out... however, I did not check the TCM which is a great idea.
I will check the TCM for visible transmission fluid leakage, as the fluid may have traveled up the wiring harness and I missed it when I looked.
So I went and got a computer scan, and this is their findings:
Vehicle does not shift properly, there are multiple codes in all control modules. The codes in the motor electronics that are causing the vehicle to be in limp mode state that there are codes in the transmission module. The codes in the transmission module pertaining to this problem are faulty signals from the rear wheel speed sensors via the ESP module. When the vehicle is driven the rear wheel speed signals are extremely erratic making it impossible for the transmission to shift correctly. To correct the problem we need to replace both rear speed sensors and the tone rings (CV shafts). This will correct the problem causing the vehicle to be in limp mode, however there may be further unrelated codes that return in the motor electronics, transmission or ESP.
Basically the tone rings (i.e., reluctor rings) inside the rear CV shaft (i.e., axle shaft) is damaged - in person they said more specifically "corroded". Now, they also said both ABS speed sensors, but the rear right one is only a few months old and the rear left one is where the muffler fell off and most likely damaged the tone ring inside the shaft.
In any case, they told me that only MB sells rear axles and that there are no after market parts for it - as such, the total cost with labour comes out to $5,000. That's steep and I can only image what MB would charge if an indy gave this estimate. They also recommended I dispose of the car, however that's not a realistic option.
After investigating, here is what I have come up with, any guidance and feedback will be greatly appreciated:
Notes
- ABS speed sensor on rear-right has been replaced recently (still shiny black) and is unlikely to be at fault or damaged
- ABS speed sensor on rear-left is old, possibly damaged, will replace it as well.
- CV shaft on rear-right is probably fine
- CV shaft on rear-left is most likely to have its reluctor ring damaged since that is where the rear-left muffler broke off and probably impacted and put the final nail in the coffin for the reluctor ring
- how to replace CV shaft details: http://www.benzworld.org/forums/w210...20-4matic.html
Option 1 - Replace Reluctor Rings in CV Shaft - $50 + Labour
Not sure how difficult this is, but there is a UK site that sells custom made corrosion proof reluctor rings for 20 GBP (pounds), probably will come up to $50 CAD shipped and all. The question is how difficult it is to get inside the shaft to replace it. On the other hand, these shafts are probably as old as the car since the car has 310,000 km (200,000 miles) on it, which leads me into the second option.
I wonder why are you exploring "hit or miss" $2000 fixes while you are avoiding to do proven $40 fix?
W211 has bulletproof reluctor rings and transmission is using its own speed sensor.
How corroded are yours?
How the vehicle speedometer takes signal was not really publicized, but suppose the program can take signal from any of 4 wheels. Meaning if one sensor malfunction, the speedo change to the other.
I wonder why are you exploring "hit or miss" $2000 fixes while you are avoiding to do proven $40 fix?
W211 has bulletproof reluctor rings and transmission is using its own speed sensor.
How corroded are yours?
How the vehicle speedometer takes signal was not really publicized, but suppose the program can take signal from any of 4 wheels. Meaning if one sensor malfunction, the speedo change to the other.
The $40 dollar fix is the reluctor rings? I'm going to take pictures of my rings now as I am at the shop and car us hoisted.
With this kind of job approval you will spend 40 grands in next 3 years.
Mechanics are real pro when it comes to milk uneducated customers.
I know that Toronto is American Capital of Corrosion, but even British don't have to replace rectangular rings on their W211.
When we have to relay on your description of the problem, statistics shows that 1000's of owners in very similar situations have been able to get cars back on the road with $40 spent.
Read the whole topic again and follow good suggestions.
You will not be the first owner who after spending $2500 learn that it was not the axles that were the problem.
07-14-2016, 10:49 AM
haha yes, pass the misery / hot potato to some other poor fella. It's mine now and I will be driving it til the rust finishes it off. I've "invested" too much cash into this one, it's pretty much got nothing left that can break or go faulty.
)
