'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

Attached Files

	PO730-1.pdf (53.4 KB, 2280 views)
	PO730-2.pdf (7.4 KB, 1689 views)

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.

__________________
Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320

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.

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

Bob

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

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator