cyeung65

Does anyone know? I am trying to buy one from Autohausz and need the part no. or name. Thanks

C32AMG/02

If you are referring to N2 and N3 RPM sensors, you will need to change the conductor plate @ $250.00 Parts only, to replace, valve body must be removed. Which codes were retrieve.

cyeung65

Yes, I know. I got P0720 and P0500, its a 2000 ML320.

Autohausz needed a more specific name to look it up, they didn't have a parts explosion.

The curious thing is that it goes into Limp Home mode, but if I warm it up over 80 C, shut it down and restart, I can get it out of Limp Home. Could it be fluid related?

C32AMG/02

I would check the transmission electrical harness for transmission fluid contamination, corrosion and any damage .The connector is on the passenger side front of the transmission, remove the metal shield, turning the tab on the connector CCW will release the harness connector. I would aslo Back probe every solenoid / sensor at the TCM with an oscilloscope, checking for proper resistance, voltage and signal readings.

Or you can just change the conductor plate, # A 140 270 07 61. Confirm this part number with a MB dealer, it may be updated. Clear all codes in all modules when done.



The curious thing is that it goes into Limp Home mode, but if I warm it up over 80 C, shut it down and restart, I can get it out of Limp Home. Could it be fluid related?


That will happen with Key reset codes.

Racin_fool

I would try to flush the fluid first before throwing a $250 part at it. Just flush the fluid and put a new filter in there.

You could also drop the valve body and conductor plate down while you are in there and just clean it off and that will more than likely take care of your problems.

C32AMG/02

You will need 16 liters of MB Z8001 107773 transmission fluid to Exchange (flush) all the fluid in a 722.6 transmission. 16 X $14.00 = $224.00.


Flush the transmission after you fixed the problem, not before.

cyeung65

Racin Fool - is this from experience? I understand C32's point. and he is speaking from experience with these transmissions.

I inspected the connector, and there is a lot of fluid seepage around it. One thing I noticed is the wires run really close to the O2 sensor and the exahust pipe. They are protected with some heat shielding but seem kind of brittle. I hate to spend all that dough on a conductor plate ($189 from BMAparts) and fluid to find out I have fried wires. Need to investigate this further.

Racin_fool

so check out the wires and see if they need to be repaired. They shouldn't, but anything can happen.

But yes, I am talking from experience. Most of the time the cars I see with this problem have some sort of extended warranty or CPO and they cover it. But I have also helped a few people out by doing this and it works just fine afterwards. A good majority of the time this happens because of particles in the old and dirty fluid get onto the sensor and cause false readings. As for needing 16 quarts of fluid, I wouldn't exchange all the old fluid for new stuff. Doing that can cause major problems in transmissions with higher mileage. We have done complete flushes on transmissions before with higher mileage and shortly after that, the transmission will fail or start to slip badly and will require replacement or a rebuild. You guys may not believe it, but sometimes having some of that older fluid in there is a good thing and can save you the trouble of having to replace/rebuild the trans.

If you just drop the pan and the valve body without flushing everything else in the system, you would need about 5-6 quarts of trans fluid to properly refill it.

If the trans conduit/connector/spacer is leaking around it, then it would be a good idea to go ahead and replace it with the updated parts or atleast install new seals since you will have to remove it to get the valve body out anyways.

If it were my car, I would probably go ahead and replace the electrical conductor/plate ontop of the valve body where the speed sensor is just to make sure the problem was solved. I generally tend to be a little **** about working on or repairing my own cars though.

C32AMG/02

I

Did you road test the car before the flush to verify shifting quality and condition, slipping, delay into gears, harsh shift, shift and TC chatter. Did you check TCM Adaptation Values and for fault codes.

In this day and age, performing a transmission fluid Exchange/ Flush in a properly working Transmission, will not cause a Transmission FAILUER. Way would It.?

C32AMG/02

Fluid in the harness will set false codes, Clean the Harness connector with Brake Clean. Replace the internal connecter / spacer with an updated one, 203 540 02 53 comes with O Rings Loosen the internal connector screw (9/32 socket) then remove the connector. Clear all codes, road test the car, recheck for codes. Safety first

cyeung65

I cleaned the connector (wire side only) with MAF cleaner and it still set the code. It was drowned in fluid, I take it that it should not be? I did this before you posted above quote. I guess I just plugged it back into a wet situation?

Also is the internal connector/spacer all accessible from the top - or from the bottom with the pan and valve body removed? Can't see too well up in that connector area.

I have the pan off and will remove the valve body next to get to the conductor plate. I will try cleaning it up first before buying a new one.

I really appreciate these professional tips from you and Racin Fool.

C32AMG/02

Loosen the internal connector/Spacer screw (9/32 socket) first, remove the connector from the top, outside of transmission, and then remove the valve body.

cyeung65

I got everything down yesterday and as luck would have it, I have one more torx bolt to take off to remove the conductor plate from the valve body...and it is about to strip. I need to get a new Torx 30 bit as mine is a cheapy and old.

What should I use to clean the valve body? Brake cleaner ok?

I may just go ahead and replace the plate with a new one since I don't want to have to do this all again. Its not hard to do actually, just time consuming.

C32AMG/02

Be careful when removing the solenoids, remove one at a time and place them in the order they were removed. Brake clean is fine, as long as you clean the valve body with solenoid installed, and don’t forget to line up the manual valve in the valve body with the shifter lever rod.

cyeung65

Got the new conductor plate on, closed everything up, cleared the codes, started up and still went into Limp Home mode. And the codes came back on.

Pulled the battery to be sure...still the same.

Any more suggestions? Would low fluid level throw the code?

C32AMG/02

Those codes on a ML are wheel speed sensors, what type of fault codes scanner are you using, pull all codes from every module.

cyeung65

I get P0720 and P0500. These were read by Autozone and by a universal scanner I bought. So the only thing to do now is take it to a shop with a DAS?

The references I have seen posted in the W163 forum say they are VSS and speed sensor output. Are these NOT the ones in the conductor plate?

I have also read posts here about Limp Home mode being solved by replacing the TCM or a module under the console? Where are these 2 in the ML? Is it any of these three?

C32AMG/02

Most Generic Fault scanners can’t Clear fault codes in a MB car or disconnecting the battery. First: with a capable scanner read and clear ALL fault codes in each and every module separately, after a drive cycle check every module separately for codes.

VSS is vehicle speed sensor, input is usually from wheel speed sensors, and inspect all four wheels for any damaged sensors, body and wires.

Output speed sensor
It depends on which control module that code was stored in, from the TCM it’s the input speed sensor in the conductor plate


Transmission control module is located under the instrument panel; inspect the Harness for transmission fluid contamination. When working on any control modules always make sure the ignition is in the “0” position. “The ESM (Electronic Selector lever Module) is the other transmission input module, which is part of the gear shift selector lever.
Post any new codes and Good luck

cyeung65

I have not had time to inspect the speed sensors at the wheels but had a thought. I recently installed an aftermarket TPMS system that transmits a radio signal to a dash mounted reciever. Could this interfere with the VSS? There is not a direct correlation in the timing when I started having the Limp Home problem - but doesn't hurt to check with anyone with knowledge or experience.

cyeung65

Took it to an indie shop after checking the wheels sensors, the TCM for transmission fuid. Turned out to be the ESP module. Definitely not intuitive from the diagnostic codes. Really need the correct scanners to figure it out which I don't have. Wish I had not spent $210 on the conductor plate. But at least I changed my transmission fluid right?

Thanks for the help guys.

C32AMG/02

Conductor plates have a high failure rate, metal contamination. You saved your self from changing it in the Future. MB Transmission Sealed for life mentality, does not work in the real world. Every time that transmission is turning the clutches and planetary are producing metal. I glad you were able to have it fix.