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'01 ML320, '02 ML500, '03 C240, '05 ML350
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Discussion Starter #1
‘01 ML320 with 130K+ miles

4 Low engaged. Truck acts like it is in limp home mode. 4-Low won’t disengage. Left overnight at location and plan to head out there later today with some tools and my scanner to figure out what is up with the transmission.

I’m going to bring some additional transmission fluid, just in case it is low and that is the cause.
Can I change the transmission connector without draining the pan?

thankd.
 

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Dallas, Texas
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Most likely TC high/low motor. Read faults in TC, ETC and engine. Take good notes. Clear faults then shift hi/lo few times and reread faults.

If you intend to replace plug adapter do that first. It can be replaced without taking pan off. If you lift front foot higher than back you will not loose any fluid. Play it safe.
 

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'01 ML320, '02 ML500, '03 C240, '05 ML350
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101 Posts
Discussion Starter #3
So, very interesting process.

Round 1: VG - no errors (although in hindsight, it is possible that there was no comms)
ETC - 116 Sporadic gear oil temp sensor (Y3/6b1) and Starter lockout contact (Y3/6b), 137 sporadic fault in CAN commo with control module N78 (transfer case) - control implausible;
ESP - C1030-000 Fault in CAN comms with VG N78 (transfer case), C1140-008 Steering Angle sensor not initialized
ESM - no errors
AAM - no communication with it (a problem I've had since I've owned the vehicle, but hasn't caused any issues).

Cleared codes, drove it around the block, seemed fine and shut it off. Loaded back up and started to head home. Drove great. Stopped about 10 minutes later to get gas, then drove another 10 minutes to return a fuel pressure test kit. Back in the truck for 15 minutes and shopping at Costco.

Sure enough, load up and head out and get the 'low range' light and clunky shifting to Drive and Reverse. Tried clearing the below codes, but nothing, so limped it the remaining 2 miles home.

Round 2 codes: VG - No communication with module ("!")
ETC - 137 sporadic fault in CAN commo with control module N78 (transfer case) - control implausible; 041 Transfer case control implausible
ESP - C1030-000 Fault in CAN comms with VG N78 (transfer case),
ESM - P2071-008 Start enable of DAS not sent
EAM - B1089 CAN fault: A55 (Transfer case (VG)) range selector motor
ICM - B1089 fault to transfer case


So, TC High/Low motor?

Thanks!
 

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'02 ML320 rattletrap at 118K miles
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42 Posts
Maybe it got wet? I think water readily enters the MLs (my left foot mysterisously gets drips of water in winter as the snow on car melts) and maybe there are modules under the seats and stuff like other german cars. I fixed a Cayenne transfer case module once by finding legacy parts from a (presumably) Russian guy in LA. Funny thing is, the drive transistors I replaced were special in that they measured the current flowing in them with Hall effect plates....but to no avail, whomever programmed the computer didn't see fit to use that data (by dropping the gate drive in high current condition--which seems the obvious use of such technology) to keep them from melting down. that module lived under one of the seats, as did a 'yaw rate gyro' (presumably in case I got big air and needed heading-hold feature).
 

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w163 02 ML500 W210 97 E50Amg w202 99 C230K w124 - need more space, time to build again
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Maybe it got wet? I think water readily enters the MLs (my left foot mysterisously gets drips of water in winter as the snow on car melts) and maybe there are modules under the seats and stuff like other german cars. I fixed a Cayenne transfer case module once by finding legacy parts from a (presumably) Russian guy in LA. Funny thing is, the drive transistors I replaced were special in that they measured the current flowing in them with Hall effect plates....but to no avail, whomever programmed the computer didn't see fit to use that data (by dropping the gate drive in high current condition--which seems the obvious use of such technology) to keep them from melting down. that module lived under one of the seats, as did a 'yaw rate gyro' (presumably in case I got big air and needed heading-hold feature).
Either your sunroof drain lines are clogged, disconnected or the cowl drain holes (on both sides) just below the windshield need cleaning from debris/leaves clogging up the drain holes. And yes, there are modules on the footwell PS, that can get exposed/drenched with water from these leaks into the cabin.
 

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'01 ML320, '02 ML500, '03 C240, '05 ML350
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Discussion Starter #7 (Edited)
After sitting all day. I was able to reset the high/low motor on the transfer case. And it drove normally (albeit from the side street into the garage). Re-ran the codes and was able to talk with the TC module (VG) - Had a P1831 (positioner motor, position sensor, or power supply is faulty).

Connections at TC module are clear/clean. Fuses 8 and 22 are good. I checked the connections on the underside of the fuse box and I have a 'rogue' green wire that is loose. Looks like it would connect to the inboard portion of the P/A plug. If anyone can confirm, that would be great, otherwise I'll pull the fuse box of one of my other MLs to confirm.

Connections at the transfer case motor also look good.

I have a transfer case motor on order and it should arrive on Tuesday (17 DEC). Although, I can hear the motor engaging when I reset it today, so maybe not the issue. It seems like something is shutting down if it gets too hot or reaches operational temperature.

Thanks!
 

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'02 ML320 rattletrap at 118K miles
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Not sure about the ML, but the cayenne xfer case motor did a couple things: engaged the different gear ratios in the 'normal' fashion; and, adjusted the front/rear torque split by 'torquing' a clutch pack in the case one way or the other. So, that particular motor could modulate back and forth without really 'spinning up' to speed to do the front/rear split task (all the time, I think). Then, with vehicle stopped, it would shift the gears and forks to change range and lock the center diff. I think they used the magic 'current measuring mosfets' because the motor could be loaded without spinning, and therefore get hot, especially the particular winding that happened to be 'across the brushes.' But they didn't bother to complete the engineering and cayennes notoriously burn up modules and motors (even with current sensing hardware built in) and the 'procedure' to fix is 'replace both' while 'bleeding cash.'

So, if the motor is still good, be ready to consider swapping the module (or at least carving it open and checking for burnt smell or obvious charred parts).
 

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I have a transfer case motor on order and it should arrive on Tuesday (17 DEC). Although, I can hear the motor engaging when I reset it today, so maybe not the issue. It seems like something is shutting down if it gets too hot or reaches operational temperature.

Thanks!
Position sensor inside motor assembly gets tarnished from lack of use.
 

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'01 ML320, '02 ML500, '03 C240, '05 ML350
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Discussion Starter #10
Put the new motor assembly on this evening and closed everything back up.

Start the truck and get the Low Range flashing a bunch of times (14?). Shift to neutral try to engage the High/Low motor. Nothing physically happens and the light stays out. Drive around, start/stop, etc, no change what so ever.

SDS after driving only has codes for the Bank 1 O2 sensor (addressing on Saturday) and the steering angle sensor not initialized. Nothing with the transfer case or anything else.

My handheld scanner (Bluedriver) showed a P0700 - Transmission Control system malfunction. No MIL as a result of the code. Did it just read it as a generic code because of the high/low motor? Shifting was normal and occurred when it should (at least it seemed that way to me).

I'll need to re-check my connections on Thursday.

Thanks.
 

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'02 ML320 rattletrap at 118K miles
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If I became convinced it was the module, I would start looking for a good used one (I am cheap) and consider cutting open the suspect one to look for burned drive transistors. I suspect the same contract manufacturer made these for many brands of cars. The one I hacked up may have been Electrolux. It's been several years since I got the mosfets from the 'russian guy' and they were obsolete back then. That model year was 2004 Cayenne and I think I did the rework of the transfer case control module around 2015. That tells me that the designers of the module used obsolete parts or the parts got obsoleted soon after the product was released to market. There was no old stock at suppliers like digikey, newark, mouser so they went obsolete, then old stock sold out, then I got lucky and found the guy in LA with some and generally obsolete electronic components take many years to sell out because of the size of the manufacturing runs.

You might not be at this point yet, and if lucky this isn't where you are going. Maybe factory new modules are reasonably priced? If it communicates on the data bus but can't drive the motor, this might be the issue. The fact that you can hear the motor trying to move may be a clue.

Another poster suggested bad position sensors....but new motor should have fixed that.
 

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Put the new motor assembly on this evening and closed everything back up.

Start the truck and get the Low Range flashing a bunch of times (14?). Shift to neutral try to engage the High/Low motor. Nothing physically happens and the light stays out. Drive around, start/stop, etc, no change what so ever.

SDS after driving only has codes for the Bank 1 O2 sensor (addressing on Saturday) and the steering angle sensor not initialized. Nothing with the transfer case or anything else.

My handheld scanner (Bluedriver) showed a P0700 - Transmission Control system malfunction. No MIL as a result of the code. Did it just read it as a generic code because of the high/low motor? Shifting was normal and occurred when it should (at least it seemed that way to me).

I'll need to re-check my connections on Thursday.

Thanks.
Make sure battery is up and does not dip on startup.

Then read PDF here.
 

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'01 ML320, '02 ML500, '03 C240, '05 ML350
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Discussion Starter #13
I have battery on trickle charger all night, so it should be full up. But, I did try the P1831 reset code procedure you referenced, and got nothing.
 

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Discussion Starter #14
Connections were all fine.

I removed the 'new' motor and put the old one back on and was able to get it to shift into high and back into low. Repeated a few times and then somewhere it got stuck and was in low mode, but no light. Shutdown of the truck was able to clear the low mode, but it wouldn't go into low mode until I drove around a bit.

Not sure if the issue is the motor (and the sensors within) or the TC module under the center console.

I'm going to source a used Transfer Case Control Module, just in case.
 
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