722.6 Trans P2502 fault code - Mercedes Forum - Mercedes Benz Enthusiast Forums

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Old 01-02-2017, 11:37 AM
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Default 722.6 Trans P2502 fault code

2001 S430. 722.6 Transmission went into limp home mode. Checked codes with iCarsoft MBII OBDII. Codes suggested and I replaced the Electronic Plate on the Transmission Valve Body as well as the Electrical Conductor which was dry of any leaking fluid. While I had it out, I cleaned the selonoids and tested them within correct ohms and clicking under 12 volt power. Cleaned valve body within a meticulously clean and lint free environment. I did not do a valve rebuild of the valve body but all appeared clean and good with no scarring. Transmission Oil Pan was a bit mucky and in need of an oil change but no debris within the oil pan or the valve body and selonoid filters. Reassembled. Fresh Transmission Fluid and Filter. Codes cleared. Operated perfectly for the day of starts, stops, up mountain driving, down mountain driving, shutting off engine, restarting engine... all worked perfectly... until a 3 mile drive on the interstate at 70mph. All seemed to upshift perfectly onto highway speeds, and downshift smoothly upon exit. At next redlight the vehicle shifted hard into first gear... then limp home mode again. I am throwing one single fault code for the transmission of P2502 (implausible gear or transmission slipping). I can clear the code and vehicle will shift into R or D successfully with a slight delay. Reverse works perfectly, but immediately as the vehicle moves forward and should shift from first to second I get the P2502 code again. This occurs the same in Winter mode or Summer mode (starting in 1rst or 2cd gear), whether moving downhill with no pressure on transmission, uphill with pressure on transmission, or on level ground with normal slight pressure on transmission. Checking the live data feed with the MBII tool it appears that the torque converter and lock up clutch are at least working appropriately up to the point of throwing a P2502 code. My limited knowledge would seem to indicate a torque converter problem, but my Indy Merc shop seems to think I have another bad Transmission Control Module, as code thrown does not vary between W and S trans settins. I can find no one else experiencing a single solitary P2502 code in limp home mode. Everyone else finds multiple codes with the P2502 code which lends clues to the source of their problem. ---anyone else have experience with a single P2502 code or solution? Any suggestions appreciated before I begin replacing parts associated with the P2502 one at a time to find the solution.
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Old 04-22-2017, 04:40 PM
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Default 722.6 P2502 fault code


Did you find the problem I have the same problem

please let me know if you did
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Old 04-22-2017, 09:34 PM
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Tag Job it is an ongoing effort. I have it in my garage working on it intermittently but still determined to find the solution. I did switch out the Transmission Control Module with one which was a known match and good... I had a difficult time clearing the codes after switching the TCM but after a couple of tries they cleared. At that point it seemed like my problem was solved. It appeared. It took a few starts and stops for the trans to begin shifting smoothly... but it was shifting through all gears and finally settled into a smooth expected performance. Up hill. Down hill. Abrupt acceleration. Sudden stop. The trans appeared to be working perfect. I then put it on the highway again and worked through all the gears up and down. Over drive perfect... even passing gear would shift it back down to third for acceleration and shift back to overdrive as I let off. All perfect. ...Until I exited off of the Interstate after about 5 miles. First two red lights the trans stopped and started perfectly. The third red light the trans acted as if it were in neutral. Fortunately my OBDII Carsoft reader was still in the front seat. I turned on my flashers and connected it. It did indeed show the trans reading Neutral no matter which gear I put it in. I then checked the codes and was throwing a weak modulator solenoid code. I cleared the code. Restarted the car and all gears worked perfectly again. It worked perfectly another 5 miles until I started up a steep grade. As it geared down it again went back into showing neutral. I was in traffic on a two way road so I cleared the code again... and the trans began working perfectly again... Once again as I drove into an S curve and slowed down... the vehicle did not gear down properly and went back into neutral again. I cleared the code and successfully brought it home into the garage.

A couple of thoughts... one the trans is actually showing the desired gear AND the actual gear as neutral when this occurs... two, it is NOT going back into limp home mode.

As I have already changed the electronic plate and the transmission control module both... I feel confident that I now need to change the 3Y Modulator Solenoid (there is a specific name but I do not have my notes and scanner with me right now)... but it does seem to find that modulator solenoid as the one common code through all of this. Others here advised me correctly I believe that this could be the culprit.

I am relieved to find that it does not appear the be the clutch packs which had been suggested... the trans shifts perfectly hot and cold... and with me changing the electronic components of TCM and Electronic Plate I think the solenoid is the logical next step.

I know my electronic plate was bad... as the speed sensor was clearly damaged as they characteristically do over time. I think when I also replace my TCM I either bought a defective one or one which had been programmed for a different vehicle (though its label matched perfectly).

Multiple overlapping problems can make these things a bear for an amateur to sort through. If the parts would only fail one at a time. Ha. I hope that helps... such as my experience as an layman hobbyist may assist.
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Old 04-24-2017, 10:03 AM
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If you guys need help repairing your modules, we can help you do that at well below dealer pricing. Check us out at Mercedes PCM ECM TCM Engine Computer. Good luck to the both of you!
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722.6, limp home mode, p2502, s430, tcm

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