siideways

So earlier today my car, which normally runs so well, suddenly decided to stop shifting in the right gear. I was driving along just fine when I came to a stop at a red light and the tranny wouldn't downshift back into first gear. So when I hit the gas, it was still in 4th or so, bogging off the line and staying in 4th even when I got up to speeds better suited for 5th/overdrive. Fortunately, I was near my destination so I parked and walked into my appt. Later, when I came out and fired up the car, the check engine light was on. And the tranny was still doing weird things, either not upshifting or downshifting or both. What the hell could this be? tranny-related or engine-related? Anyone know how to read engine codes?

03'55AMG

With a code reader?? Go to autozone and have them pulled for free

503C43 ////AMG

Could be your electronic gear selector switch but if it threw a CEL I would guess this is not the case, what happens when you manually shift?

P.S. You really need to pull the codes (and post them here) if you can to be able to determine what the issue is.

siideways

Took it to a local shop and turns out it threw numerous codes. Guess one or more of the solenoids have gone bad w/in the valve body...they're gonna keep diagnosing to see what other issues there may be. Ugh...guess the 5-spd trannies in the 97 C36 and all C43s aren't as bullet-proof as we would all like.

ohlord

said they were bullet proof? The weakest link in the whole drivetrain is the 722.6 5 speed.
Post the codes,it could be the fluid intrusion into the tcu. It could be the failed conductor plate. It could be the noids.
It could be the old girl took a lickin and no longer is tickin

MarcusF

Could be an input speed sensor. It could also be the plate the holds the sensor. Either way, it's an inexpensive fix. About $540 in labor from a dealer. That includes the trans wiring o-ring job (a $2 part). I had it done in 2008. Here's a thread I started when mine failed:

https://mbworld.org/forums/clk-class...nsmission.html

ohlord

conductor plate $178 and not so hard of a diy

siideways

So the guy at the shop initially told me that they would likely need to replace/rebuild the valve body, but upon further inspection (and review of some old MB technical service bulletins) now says that the problem may not be mechanical in nature at all. He thinks (and hopes) that it may be electrical in that the transmission wiring harness is so close to the cats that one or more wires inside may have melted, causing the numerous codes indicating that all solenoids have gone bad. If the problem is truly this simple, he's confident that replacing/soldering the affected wires should do the trick...does any of this jive with you guys?

RANDY_P

should be an easy visual verification. The only problem with that theory is why is that just happening now?

Can you get it to engage other gears via manual gearshift?

rjp

siideways

Well, actually, it did it twice before. The first time was not long after buying the car, it wouldn't upshift from 3rd gear on the fwy until I pulled off, shut down the car, and fired her back up. Problem never re-occured until about a month ago, this time it wouldn't downshift when coming to a stop, causing me to start in as high as 4th gear, bogging off the line. Again, turned it off, problem went away. And then finally this episode, w/ the check engine light.

And no, I cannot get the gears to engage via manual shifting...no effect.

siideways

So the latest update is that it is the wiring harness, but not the main one, rather the one that runs from the ECU, through the floorboard, and down to the tranny. I didn't know there's more than one wiring harness, but I'm told the main one is far more costly (both the part and labor to replace it). Ugh...guess I'm grabbing my ankles. Hopefully this will be the last major ticket item to replace/repair on this thing.

PS - BTW, I thought it was only the earlier C36 models (95 and maybe 96 as well) that had wiring harness issues?

DRBC43AMG

Sorry to hear your problems, but seem you have found another wiring harness issue

fredtga

What CEL codes did you pull?

Is the ASR light on? Does the brake light work?
I would start checking the brake switch and ABS sensors. ABS sensors must have resistance between 800 - 2100 ohms.
It happened to me that the gearbox got stuck in a gear and turned out to be the ABS sensor at the differential. The CEL was "speed sensor malfunction".

If it's not that, valve body is very easy to pull and again you can check each solenoid for the correct resistance. While you're at it, check also the springs on the side of the valve body, they tend to break causing hard shifts.

siideways

Nah, ASR light wasn't on. They had inspected all mechanical aspects of the tranny itself, and it was fine, i.e. fluid was the right color, not burnt, no metal shavings, etc. Then when they inspected the wiring harness, they saw a number of wires all bunched up just past the banjo fitting, and when they tugged on it slightly, it re-lit all the solenoid codes again, hence the culprit.

ohlord

above.
Most likely not the wires themselves,but the common problem of trans fluid intrusion from the leaking o ring electrical connector leaking fluid up the wire harness to the tcu.
you open up the tcu clean it with crc maf cleaner remove the electrical connector and install the new upgraded with o ring and dry the wires out.
search google 722.6 electrical connector leak
common problem easy solution.
So while in there make sure they also examine that as a possible and if not since they are there anyway get the under 10 buck part and r/r it to remove another potential problem in the future