2003 c230 722.6 transmission issues - PeachParts Mercedes-Benz Forum

cgoodwin · #1 03-05-2016, 12:23 PM

Start vehicle and it will shift into PRND and you can run through 1234

After a minute or two it goes into neutral regardless of the gear position. At this point you can no longer run through 1234 but can still shift DNRP and the changes are reflected on the instrument console.

Shutting it off for a few minutes allows you to repeat the process but if you shut it off and restart right away it is just in neutral.

No codes present
Fluid level ok and does not smell burned
No odd noises
No previous symptoms
Examined plug and found it wet. Replaced socket and cleaned connector well.
Examined harness and TCM found both wet and cleaned thoroughly.

Any ideas on how to determine if the issue may be the connector plate or valve body???

MAVA · #2 03-06-2016, 09:38 AM

You've cleaned your TCM something like this...

To clean the TCM:

A) Pull the TCM from the car it will easily slide out once the connectors are off.

B) with a long flat 7"-10" flat screw driver with a blade with of 1/4" or 5/16". Slide the screw driver near the end(about a inch or so) on the long side of the case between the case and the connector. Just insert it about an inch down. Slide it down to the center, and twist the screw driver, and the case should break the glue joint. Do the same for the other side. hold the screw driver, and get another for the other side, so you can remove the case.

C) poor the oil in a bucket

D) clean what you can with paper towels.

E) get your 20oz contact spray cleaner, and wet it down. I like to blot(pat dry it) it dry while wet. Spray around the chips. Do about six to eight applications(spray and clean with a new paper towel). The last one clean it dry..

F) let the board dry standing up...

Cleaning the connectors:

A) the connectors have a cable tie on the end. Cut it off

B) the connector cover will slide off

C) spray the pins four or so times. Blot between sprays. Remember to have a rag underneath, so the stuff does not cross contaminate.

Again do this only if you find oil in the connectors..

Let it dry overnight on one edge...

Most will say you need a conductor plate, but a conductor plate would still give you limp mode home condition of 2nd and reverse, yet you may have a failure of it to, but you will need to inspect it for cracks like in the picture in post 35..

http://www.peachparts.com/shopforum/tech-help/325722-722-6-transmission-refresh-diy-questions.html

Not sure if the 03 C-Class still had the first generation 722.6's or the second Generation.. The first generation 722.6 have a spring that breaks/shrinks with time, and your could have that problem, yet first generation 722.6's have a interlock cable at the back.

Regulating Pressure Control Valve Spring - 68942-01 - Sonnax

More than likely you a problem with one or both regulation solenoids(they are black), and cost about ~$250 each, but I would go to the Self-Serve junk yard and get them +2000 722.6 equipped E or S class, or get the whole valve body for under $100..

Row52 | Self Service Yard directory. Find automotive junkyards near you.

All the best,

Martin

cgoodwin · #3 03-06-2016, 11:47 AM

Yes I cleaned the TCM well, truth be told I found no oil in the unit itself, just on the floor and the harness, regardless, I cleaned the unit well, inside and out, with electrical contact cleaner and compressed air. I also took apart the connectors and cleaned each one as well as the harness.

After I had the exact same fault.

On cold start I can shift into both R and D and the trans engages, I can also walk it through 1234 using the shifter and all changes are indicated on the dash display.

After less than a minute it disengages although the dash indicator still shows the gear selection. At this point I can move the selector through the gears, all are reflected on the dash, however I can not toggle between 1234 and nothing will cause the trans to engage.

I clearly still have communication between the shifter and the TCM since selections are reflected on the dash, but engagement is completely lost and the worst part is that I am getting no codes.

I suspected that perhaps my Snap-on Solus could not read trans codes so I put a very nearly dead battery in the car and cranked it until flat. I then read trans codes and got a p2600 circuit 87 voltage low showing that the TCU had seen low voltage - so clearly the Solus can read at least some codes. I also ran the vehicle with the TCU completely unplugged, but this threw no codes???

I am very familiar with the valve body kits by Sonax and with the Contactor plate, but I would like to be sure before throwing more money at the issue. If I had a telltale code like speed sensor etc I wouldn't hesitate....

Has anyone heard of these symptoms???

cgoodwin · #4 03-08-2016, 10:46 AM

OK, changed the contactor plate out, improved the issue slightly, or the complete fluid flush at the same time improved the issue. However the same issue persists exactly.

Checking the trans on the scanner I find that once the trans has disengaged the gear selection on the scanner shows that the selected gear is D or R but the actual gear remains N. This eliminates any electrical issues since it is showing the correct selected gear at the TCM and the valve body is showing that the actual gear is in fact N. I do not believe that the issue is with the TCM since it locks up and selects gears at first so the issue must be mechanical in the trans itself.

The fluid was burnt smelling and the valve body was filthy, the finish on the solenoids showed some corrosion, the radiator is a Behr and the dip stick locking cap had the tab broken off so I believe that at some point the radiator leaved coolant into the transmission and was changed and the trans flushed. It seems that this bought a year or two more use but that the trans is now trash....

I'll be pulling it today and salvaging the parts I can (new contactor plate, plug and probably the valve body) and replacing it with a used unit.

MAVA · #5 03-08-2016, 03:14 PM

Can you share some pictures of the valve body?

Maybe one of the two black solenoids froze, and they are the heart of these 722.6's

In case like this, yes it may be practical to do a swap, but I'd rebuild/update it with a generation 2(touch shift car) internals. If your interested in doing a diy on it, I got lots of info.

Martin

Martin

cgoodwin · #6 03-10-2016, 06:53 PM

A stuck solenoid would cause a poor shift or a stuck in gear condition, that is not what I am experiencing.

I have done the connector, tried a known good TCU, replaced the contactor plate and nothing has changed. After about 2 minutes the trans goes into N and will not come out until you shut down for two minuted, then it does the same again. I am thinking it must be something in the pressure pump but at this point replacing it with a known good used trans seems to be the best option as the trans is the same cost as a rebuilt valve body....