P2502 Fault code

[mercmad6.3]

i have a MY 02 270CDi ML with the 722.6 trans . I have replaced the trans with as low mileage used one (the original one had a catastrophic failure at 260,000 ) But i have since replace the contact plate three times ,the TCM three times and tested the solenoids which are all OK . But it refuses to go into 4th or 5th . Once it goes into 4th it goes straight into limp home mode,in 3rd gear so the touchtronic shift stops working . Last week I pulled the valve body out again replaced the contact plate,pilot bush etc with genuine mercedes parts instead of chicom knockoffs and still i get P2502..
Now the problem as it sits right now
the scanner (isoft) tells me I have no DTC's in another circuit but the TCM says i have code P2502 trans slipping or implausible gear... Thats OK, but without driving the vehicle etc , the scanner cannot remove the code. Is this normal or is the TCM fualty ...again ?

PS i have washed ,stripped cleaned all the wiring loom plus the other looms connected with it to remove all trace of the old trans lube.

[97 SL320]

Stop randomly throwing parts at the car.

You need to confirm that the internal trans gear ratios are proper. There are at least two ratio sets for USA cars and a bunch others from when Chrysler was part of DB.

Also, If you have a 2 speed transfer case I'm thinking there needs to be some way that the TCU knows the transfer case is in a different speed. From another thread in a rear drive car, someone swapped rear ratios and hit limp after the trans shifted into 4 th. It drove just fine when kept in 3rd. Apparently the TCU checks that trans input and output shaft speeds match what is expected from wheel speed.

[mercmad6.3]

Hi, the trans is from exactly the same type and i am sure the 270Cdi W163's were all the same . At the thousands these parts cost, i am not likely to be throwing random anything at it. :-) It has the same transfer case . A transfer case fualt would be indicated on the scan ,but as i mentioned there is one code, P2502 and the scanner will not remove it. I see on lots of other posts that P2502 is removed with a scanner on their cars,regardless of which model, but it comes back. Mine is not removable , I just get a message say the code removal was unsuccessful. Just to recap, P2502 is trans slipping or the gear is implausible,which to me says the TCM cannot determine which gear it is in. And the trans isn't slipping it's very positive in the gears it does select. I wish i could find a TCM repair service.

[97 SL320]

Originally Posted by mercmad6.3

Hi, the trans is from exactly the same type and i am sure the 270Cdi W163's were all the same .

There is a number on the side of the trans 722.6xx , are the xx numbers the same as the old one?

Originally Posted by mercmad6.3

At the thousands these parts cost, i am not likely to be throwing random anything at it. :-)

Installing 4 conductor plates and 3 TCU is throwing parts.

Originally Posted by mercmad6.3

It has the same transfer case .

Got a wiring diagram? If there is a high / low range switch not sending a signal to the TCU, the TCU may think the transfer case is in low when it is in high.

Originally Posted by mercmad6.3

A transfer case fualt would be indicated on the scan ,but as i mentioned there is one code, P2502 and the scanner will not remove it. I see on lots of other posts that P2502 is removed with a scanner on their cars,regardless of which model, but it comes back. Mine is not removable , I just get a message say the code removal was unsuccessful. Just to recap, P2502 is trans slipping or the gear is implausible,which to me says the TCM cannot determine which gear it is in. And the trans isn't slipping it's very positive in the gears it does select. I wish i could find a TCM repair service.

Does this have a under hood 38 pin diagnostic connector? Are you plugging into that? If car has 38 pin, that is the only place to clear the codes.

[mercmad6.3]

Hi,Trans is identical in all respects. I replaced the parts as they were chicom copies ,one contact plate was actually missing a pin. The second had the metal strips inside touching each other ,which blew the first two TCM's before i realised what caused the power supply in them to fail. This TCM is new as are the contact board and pilot bush and are genuine OEM .I have all the circuit diagrams and pinout readings which all show the electrics should be in order .High and low work independently of the actual trans ,the speed is determined by the two round magnets on the contact plate,so... the low function works perfectly . these are constant 4x4 BTW. i am using the only scanner out plug which is the usual OBII plug under the dash. I have set up faults in the other systems deliberately to test my scanner and it clears them just as they should but this one has me beat.