97 S420 Transmission Trouble - PeachParts Mercedes-Benz Forum

hpf1 · #1 03-14-2009, 03:58 PM

Hi guys,
I have searched the threads and can not find anything similar to this. Any thoughts of what the problem might be. The check engine light came on and the car went into limp mode. I took it to an Indy and he read the codes and said that there was something going on with the transmission.

He cleared the codes and said to drive it home and bring it back for him to next week to read the codes again and do a full diagnostic on it. Went home and the tranny problems became noticeable. Slight lag from a stop light. Put the car in reverse and nothing, then into drive and nothing (no tranny engagement). Turned the car off and restarted the car and was able to put into reverse and drive. Parked the car in garage. The car has 187k miles.

Thanks for the help.
Tom

TMAllison · #2 03-15-2009, 12:07 PM

Check the plug on the right front of the trans where the harness connects for fluid contamination. May need to strip the sheath back to confirm. If wet, follow harness up to ECU and look again.

jvmaxime · #3 03-24-2009, 10:28 PM

Hi,
I want to thank you for all the info you have placed in this forum. However, I am having the same problem but with some few changes. My ASR, Low oil level light, check engine light are on. and the temp gauge, RPM gauge, oil level gauge quit to work. The transmission still shifts but very hard shifting. I would turn the ignition off and on and all functions would begin to work again and the transmission shifts smoothly until it happens again.
Few things that have noticed after reading your treads:
1. Found a lot of fluid in the data connector to the unit.
2. Fluid is very dark (brown) Probably old.
3.DTC shows P1747 pressure control solenoid circuit short.
I have 3 questions.
1. Should I have fluid at the connector at all?
2. Will fluid come out while replacing this part?
3. Is something inside that unit causing the connector to leak?
This a 1997 s420 with the 722.6 box. The car has 140,000k
I put 25,000 miles in it since purchased 3 years ago.
I could use any help you can offer.
Best regards,
Max.

TMAllison · #4 03-25-2009, 12:41 AM

JVM - I'm not certain what your issue is; one of the techs needs to chime in to provide more input.
I find the following for your code: P1 747 Electronic Gear Selector Module: Defective Interaction of CAN with control unit A1(instrument cluster)......that might play into your other dash instrument issues too. Does the W140 have an OVP or K40 relay like the W210 suppying power to those devices???

You should NOT have fluid at the harness connector. You need to check the opposite end where it connects to the ECU as fluid contamination wicking up the cable can fry the computer. It should not leak when replaced.

The dark fluid is not necessarirly bad; mine was brownish and smelled like 80/90wt gear oil when I changed it. 1999 S500 with 722.6 Automatic Transmission Filled for life? Sounds like it is overdue for a fluid and filter change at the least. MB fluid only. Use fluid for the 722.6 or newer 722.9 only. No equal. Will need the factory dip stick tool (dimensions posted on this site if you want to make your own) to check fill level when at 80C; the sealed trans dip stick tube is empty.

JRS · #5 03-26-2009, 02:50 PM

Quote:

Originally Posted by TMAllison

Check the plug on the right front of the trans where the harness connects for fluid contamination. May need to strip the sheath back to confirm. If wet, follow harness up to ECU and look again.

Hey TMAllison,

When you've seen this wicking: does the fluid, a) wick up the harness OUTSIDE of the wire insulation (making the wires look visibly "wet"), or b) wick up the copper strands INSIDE the wire insulation (which would make the wicking difficult to see by looking at the wires)?

Thanks!

TMAllison · #6 03-26-2009, 04:30 PM

Fortunately, has never happened to mine.

It usually wicks up the protective sheath to the computer and then shorts it out.

JRS · #7 03-26-2009, 05:16 PM

OK, thanks. I'm just wondering if it's possible to see if the wicking is occurring, by removing the cover that houses the TCU under the hood and looking at the wires going into the TCU.

If the fluid is traveling up the sheath, it sounds like it would be telling to examine the wires going into the TCU and see if they appear wet.

david s poole · #8 03-27-2009, 12:36 PM

the fluid wicks up the copper wires and thence into the computer.locate comp.disconnect and stand upside down[with connection pins down] on white paper for a few hours.this will tell the tale.seen it myself a few times.there should also be NO FLUID in the connector[called a conduit connector by benz].this problem is so common that i keep 3 in stock.you will lose approx 1 litre of fluid when you take old part out[7mm head screw].

JRS · #9 03-27-2009, 01:04 PM

Thanks David, that's really helpful. On a '97 W210, is the TCU the black box toward the windshield? (rather than the computer with the cooling fins)

david s poole · #10 03-28-2009, 04:31 PM

i think the tcu is in the module box on pass side over by fender.i believe that it is the second one counting from he front.the first is the k40 which has lots of small plugs in it.the tcu has two plugs i think.

JRS · #11 03-28-2009, 05:41 PM

Thanks, appreciate it.

jvmaxime · #12 04-10-2009, 10:27 PM

Hi everybody,

I think with all your help, I may have found my problem with this 97 722.6 gear box.
After I read your posts, I decided to investigate the problem. I went and replaced the connector at the gear box. I found alot of fluid in it and since the connector was only $8.00 at Germanparts.com, I went ahead and purchased it. After I replaced it, I still had the same problem. So I did some more investigating. I went to locate the TCM (transmission control module). It is under the hood inside a black box with a yellow sticker that said Battery in trunk. As soon as I removed the harness to the left of the module, I notice ATF at the connector. I then removed the module out of the box and laid if upside down on a white sheet of paper. I had so much ATF coming from the module I said "

I can't believe it's not butter" I cleaned the board out with electric spray and let it dry overnight. I have some pictures for you all. In a few days I'll let you know if the problem is fixed.
Best regards,
Max

jvmaxime · #13 04-13-2009, 07:02 PM

Hello everyone,

I am glad to say that my problem is fixed. No more CEL with code P1747.
I spent $8.00 for the data connector and $15.00 for 1 quart of ATF from the dealer to make up for the ATF loss during replacement. $3.49 for the electric cleaner and 2hours of my labor time. I don't think I did too bad.
Best regards,
Max.

JRS · #14 04-15-2009, 11:20 AM

Quote:

Originally Posted by jvmaxime

Hi everybody,

I think with all your help, I may have found my problem with this 97 722.6 gear box.
After I read your posts, I decided to investigate the problem. I went and replaced the connector at the gear box. I found alot of fluid in it and since the connector was only $8.00 at Germanparts.com, I went ahead and purchased it. After I replaced it, I still had the same problem. So I did some more investigating. I went to locate the TCM (transmission control module). It is under the hood inside a black box with a yellow sticker that said Battery in trunk. As soon as I removed the harness to the left of the module, I notice ATF at the connector. I then removed the module out of the box and laid if upside down on a white sheet of paper. I had so much ATF coming from the module I said "

I can't believe it's not butter" I cleaned the board out with electric spray and let it dry overnight. I have some pictures for you all. In a few days I'll let you know if the problem is fixed.
Best regards,
Max

At the suggestion of someone here (sorry, I forget who it was, but it was a great idea ....), I removed my TCU and drilled 2 small holes in the bottom of the case for drainage. Should be cheap insurance if that connector starts to leak again.

jvmaxime · #15 04-15-2009, 12:21 PM

I like your idea. I think I'll try it this weekend. I have one final question. I know that it was because of the ATF on the board I was showing the code P1747. Does it 100% mean that ATF is a conductive liquid? I asked because the same fluid seats all over the conductor plate inside the gear box where all the electronics are exposed. That confuses me a whole lot.
Best regards,
Max.