Diagnose/Repair P0730 on 722.6 - Mystery Fault
 

'98 CLK320 Replaced diff & trans fluid & filter, rear brakes, cleaned most connectors: Now MIL, limp home mode, only code = P0730 (improper gear ratio).
Code will clear with ODB II, but remains in limp home. Star Diagnostics will clear code and return normal shifting, but only for 10-15 miles. ODB will clear code, but trans remains in limp home - I can't clear the DTC's with my scanner. I pulled the valve body, cleaned it and checked all springs/valves/solenoids (to the extent I can with voltage pinouts and ease of movement checks). I did not replace the conductor plate, because all known (to me) voltage & resistance tests showed functional. Range recognition sensor also shows proper voltage values. TCU is dry, as is harness. I am not tech, or even a mechanic, just a guy who does the research and likes to spend a weekend under the car.
*Notable is that with ODB, the P0730 will clear and MIL goes out (limp home sticks though), but upon startup - with no gear selector or pedal actuation - the P0730 will immediately show up as "pending" with ODB. I am stubborn, and have spent so much time on this that I have to finish it myself. I read a reference that in an extreme circumstance, MAF or other flow issues could create this error. This seems unlikely to me, but I haven't spent a month on this because I'm smart. Does anyone know if an intake problem or something south of the torque converter could cause a gear ratio code. It seems relavant to me that the code immediately appears as pending, before any gear is engaged. Remember, I changed rear brake pads, diff. fluid, trans fluid & filter, just before this happened, so I could have screwed any number of things up. HELP!!!

I found these in WIS for PO730:
Check oil level, and check filter

All checked - except for ground
 

Thanks for the reply - I have an alldata and EPC subscription, so I have checked all the usual suspects. The only thing I never verified was the harness ground - which did appear on the alldata list, but I just assumed that a ground fault would show up in other systems. i will check it tonight (or tomorrow - very cold tonight). I have been thinking of WIS software and possibly some laptop diagnosis equipment (the $50 ODBII is obviously not quite sufficient). Any suggestions?

Sounds like wiring harness to me. I'd check it again. Even though it's dry it may be cracking insulation or the connector is dirty.

Or I could go through another 20 Q's of trans. fluid..
 

I will try a pure harness test. If I unplug it at the trans., should I test the inbound pins at the TCU (assuming I can identify them) for resistance? Or will they sow up outbound as ground faults?
FYI: during this process, I did manage to verify that the new Chrysler/Mopar ATF+4 spec trans. fluid is definitely Mercedes Spec. - at about 1/5 the price.

First of all; once the code is stored in the trans computer it must be erased from that computer then the ODB2 code can be erased.

ODB2 scanner can't erase the code...MB scanner must be used

muskratbenz, this is huge news (to me!). How did you 'verify' this fluids use for 722.6 trans? TIA,

Bob

have you checked the conduit connector in the upper right side of the trans? these are well known for needing replacement[one of those very cheap parts when benz knows it has a problem] because the o rings leak and fluid gets into the wiring.in some extreme cases it has been known to crawl up the wiring[inside insulation] to the computer.i have removed computer and let sit upside down overnight on sheet of white paper to prove.

Harness - and fluid
 

I know the fluid, if it walked up the harness, did not make it to the TCU. I did notice some abrasion wear at an exposed attachment point by the firewall. Will have to check that when I check the ground later today. Possibly fluid got inside harness and is conducting the ground to the chassis there.

Regarding the fluid "verification". Okay - that might be an exaggerated statement, it's not like I had a lab do the testing or anything. I found an excellent Chysler Crossfire manual in PDF online (huge file: 80MB, over 3000 pages). The Crossfire uses the MB 3.2 and the 722.607 transmission, so this manual was a great tool. I actually picked up some parts at the local Chrysler dealer, and noticed that they still had the german manufacturing stampings, and came in the exact same bag as the MB parts. Then I noticed the ATF+4 fluid for $4.00 a quart (later found it for $3.00). I talked to the Chrysler techs, the MB techs, and a Pennzoil rep who I happened to meet at the local NAPA. All concurrred that there was - and could not possibly be - any difference in the fluid, as all the new fluid specs for both manufacturers new models are "Daimler/Chrysler" fluid.