HELP!! ML350 ESP problem has me stumped!
 

Hey every one- newbie here and found the forum while researching a problem we have in our shop. This truck is driving us crazy and I've hit a wall thinking about it. So here's hoping another master tech out there has run into something similar or can look at a scope pattern and tell me what it is!!
This is a 03 ML350- sets curent code C1130 in the ESP as soon as key is turned on- will not erase!! The code is for RR wheel speed sensor-line monitoring (which seems to mean that it is seeing something in shouldn't in the line to that sensor). Car sitting still, RR is sensing 0.4 mph.
Here is where it gets weird- if you unplug the harness at both ends (so no sensor plugged in and no control unit), the wires from that sensor have a pattern in them- Key off!! Main harness was replaced, as MB thought it was the problem- no luck- same thing. It is obviously an induction of somekind, but we have most of the truck unplugged- still there- we can make it stop with unplugging connector #4 from the AAM- tryed a new AAM, same thing. I think the key to this is in the pattern , but I'm stumped as to what it could be- I tryed attached the patterns below, but there are too big, please let me know if anyone wants to see them- I will email them to you- the slower pattern is when the truck is completely at rest, the one that looks like a parade is when the door is open and the dome lights are on.. Any ideas??

Send me the pattern: steveb@atlantic.net If nothing else I'll resize it and post it.

Are you sure you aren't reading florescent lighting from your shop? What is the frequency?

Seeing as the other 3 sensors don't show it, and the ESP module reads it as that wheel is moving, I can't see it being from the shop- I sent you the pics, Thanks!!

Steve, if you can post the scope pattern I'd like to take a look too.

Here are the patterns, obviously not florescent lights, especially the one with two spikes.

They are really low voltage though. Have you checked the bias voltage from the controller to see if it exists on the wire with the signal. Those sensors are hall units I think, so I'm not sure what the controller sends out if anything.

PS: that looks like a MODIS, you should be able to take the patterns from it electronically sort of like the pico grab I post below
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This is a good topic for a new thread entitled, Wave Forum diagnoses :)

Does the truck have lighted sill plates?
Which connector on AAM did you pull A4, B4,..or was it on the F1 fuse box
instead?
DR.D

Dr. Diesel- no lighted sill plates, and the connector was right off the bottom of the AAM (there are I think 5 connector holes plus the RF antenna)- as near as I could figure out from the markings and diagrams, it is connector 4- A is one side of it and B is the other- been a while since 163 training and it's wiring is kind of different than other MBs to say the least!!
Steve- not a Modis (although I'd like one!!)- its a Matco version of the newer OTC scope. These patterns are plugged into the harness with the sensor and the controller unplugged- at the module end of the harness!! It has the new style sensors in this truck, so all the SDS tests are wrong-they are all written for the earlier style system.
The thing that confuses me is that it looks like a coil collapsing on the pattern ( the AC voltage), and we have unplugged every motor we can think of, and its still there....
Thanks for your help guys.....

I'm a little confused by your scope settings. It appears you are set for AC and the measurements are looking like less than .2v. I'd much rather see DC and I don't think the controller will see that level of voltage. I think most transistors need .7v to count. (or something like that).

I have seen cars with speed readings other than zero at a standstill with no problem.

Can you attach another sensor lead to where the RR would attach?

Can you isolate the cable from the loom and make it like a twisted pair ?
This would reduce or illiminate any inductance from nearby wiring/rf.

If the door activates a continuous signal rather than when closed, it seems that the Activity module plays some part...or did you unplug that too ?

Presume there is no line activity with battery ground disconnected... ?

Does car have a radar detector and/or a back up assist system?


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Steve, that is set on DC, but the scope will show AC if its there apparently (says so in the manual). But switching the sensors- haven't done that yet- the LR is right next to it in the plug- because I'm starting to wonder if it is the control unit..if it didn't follow those wires, then that would prove it.It could be that we are completely chasing our tails with this signal, other than the code, which seems to be telling me there is something wrong with the line.I say seems to, because I haven't been able to find a good description yet.

I was headed towards the twisted pair wire idea on Friday, and I decided to take the weekend and think about it first!! We tryed the AAM out of our RAP truck and same thing. No radar detector and no parktronic. Yes if you pull the battery or the #4 connector off the AAM- goes flatline, like the other sensors

Just wondering out loud....Did you check for diode blockers on the schematics at :http://www.startekinfo.com/StarTek/

or any bulletins on this problem.?


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I'm not sure, but now that I think of it I seem to remember a DTB regarding ML wheel speed sensors. Maybe something about water in the connector??? I get lots of 220's with this problem. If anything is spilled on the rear seat, it finds it's way into one of the rear wheel speed sensor connectors. I'll check first thing in the morning and post if I find anything.

Has the vehicle recently had tint applied to the windows....I remember MB saying the door modules will cause problems if the soap used to apply the tint gets into the lock electrics and will cause AAM to set DTC. but I think that was an 1140 code.

The other bulletin was misalignement of rear wheel sensor ring causing speed sensor to send false signal....