Thank you for all of your suggestions. Below you will see an update on our progress. We have purchased a Right Rear Wheel Speed Sensor in the US and it should be in Morocco in a week. Time will tell if that fixes the issue.

Here is an update on the last two days of troubleshooting:

1. I cleaned the connectors at the right rear (RR) wheel speed sensor and at the ABS brick - did not fix
2. I slightly moved the pins of the RR wheel speed sensor’s connector to one side to promote a better connection to the Sprinter’s wiring harness - did not fix
3. I ohm’ed out and found the RR sensor’s pins on the ABS connector. I slightly moved the pins of the ABS brick to one side to promote a better connection to the Sprinter’s wiring harness - did not fix
4. I hard-wired some 16-18AWG wire from a few inches away from the sensor to within a few inches from the ABS connector - did not fix

Adding the wire for #4 above essentially carries out Dennis’s (lindenengineering) temporary slave harness idea.

To my satisfaction, I have thus eliminated the following:

1. All but a few inches of the RR wheel speed sensor’s wiring.
2. Sprinter’s RR wheel speed sensor's connector.
3. All but a few inches of the Sprinter’s RR wheel speed sensor to ABS brick’s wiring harness.

I have not completely eliminated the following:

1. RR wheel speed sensor itself
2. The tone ring which is integral to the hub
3. The Sprinter’s wiring harness connector to the ABS brick
4. ABS brick

Also of note is that I discovered which menu has all of the individual wheel speed sensor’s data within our iCarsoft’s MBII. All four of the wheel speeds are essentially the same including the RR.

To me, this a big clue that the sensor is actually working. I am guessing there is some kind of “analog” issue that is out of range on the sensor. For instance, maybe a slightly too high or low resistance at the sensor. The digital data seems fine since the RR wheel speed is identical to the other three.

At this point, I would be saying: “**** it! Let’s roll down to Western Africa…” But…

I went to put the Sprinter into All Wheel Drive (AWD) after one of our test drives. It would not go. My conclusion is that these three amber warning lights preclude the operation of AWD. Can anyone confirm this? Is there a workaround for this AWD lockout?

Given that the RR wheel speed sensor data seems fine, I am surmising we have a “soft failure” of the sensor. This is item #1 in my “not completely eliminated” list above.

Item #2, the tone ring, seems unlikely to be the issue. It spins and the wheel speed sensor reads it. I guess it’s possible that the tone ring is “weak” (whatever that means) and the Sprinter’s computer is reading a "low-level” on the pulse train signal coming from the wheel speed sensor. Again, this seems unlikely to me.

I guess I could troubleshoot Item #3, the connector, by taking the ABS brick out of the engine bay and taking it apart. Then, I could ohm out the connector pin to wiring harness connector socket. This seems difficult and may require a brake system bleed. Anyone have any idea or procedure for this?

Finally, Item #4, would mean buying a $2000-$3000 ABS brick. I’ll hold off on this until we try a new wheel speed sensor.

So, we have a friend coming to Morocco in a week. We are hoping to source a sensor at his local MB dealer and have him bring it over with him.

If anyone has any other ideas or can poke holes in my troubleshooting or conclusions above, feel free! For instance, Cheyenne in post #10 above did point out I could have two failures. A new wheel speed sensor should eliminate one of these…

Thanks again!
Ryan

Hi Ryan:

Nice writeup of what you have done so far, thanks for taking the time to document your troubleshooting efforts so thoroughly.

From a distance, all I can do is study your results from a "Principles of Troubleshooting" and "Paths of Influence" perspective. By "Paths of Influence", I mean identifying and then ruling out faults on components and/or signals and/or conditions that are required to enable the functionality you are not getting (ABS, ESP, ASR).

To this point, it appears that you have approached the problem by trying to find and identify a specific fault in the system. I think that it might be appropriate - now that you have gathered so much information - to look down the other end of the telescope, so to speak, by trying to rule out (eliminate from consideration) components and/or signals and/or conditions that may be causing the problem.

For example, you wrote "I discovered which menu has all of the individual wheel speed sensor’s data within our iCarsoft’s MBII. All four of the wheel speeds are essentially the same including the RR."

That is a huge finding. If you can read individual wheel rotation speeds off the CAN bus, then that completely rules out any kind of hard fault (non-intermittent fault) with the individual speed sensors, the tone rings, and the wiring harness. Period, full stop. There is no point in doing any more troubleshooting of the portions of the system(s) that detect wheel rotation speed. You KNOW that whole sub-system is working, because you can read the wheel rotation speeds.

You also know that the portion of the ABS controller that receives, interprets, and puts that wheel rotation speed information out on the CAN bus works, because if it didn't work, you would not have been able to put that data out on the CAN bus.

There's still a possibility that you might have some form of intermittent fault within that wheel speed-sensing system. That hypothesis is supported by your earlier report that the system worked fine for 2 hours of driving, then the fault condition (indicated by the warning lights) re-appeared. But, although that is worth further investigation, I suggest you don't allow tunnel vision (focused on the wheel speed sensing system) to develop - the fault might be triggered elsewhere in the logic that governs the operation of ABS, ESP, and ASR. For example, there is probably a yaw sensor somewhere in the vehicle that supplies yaw input to the ABS. There is also a slip-ring system in the steering wheel that supplies steering wheel position input to the ABS - this input is essential for ESP functionality. Last of all, there is the electric switch on the brake pedal that activates the brake lights and informs the ABS controller that braking has been applied.

You might think that the brake light switch is not worth looking at, but it is possible that if the vehicle thinks that braking has been applied for a long time, it's a fault condition. I have found a brake light switch to be the root cause of an otherwise impossible to troubleshoot problem with an automatic distance regulation system on a complex Volkswagen vehicle.

I suspect that you are perseverating on the wheel speed sensor - specifically the right rear one - because that was the fault you were presented with when you first started troubleshooting a week ago. You may well have permanently solved that problem. If that fault is no longer being reported, stop looking at it.

Finally - most manufacturers provide their technicians with a diagnostic flowchart for use when troubleshooting complex system problems. The flowchart is basically a set of Booleans - it has an entry point, you rule out different contributory components as you work through it, and various exit points (actions to take) are presented depending on what you find.

Do you have a contact back in Europe who might be able to get you a copy of such a diagnostic flowchart? It's possible that in this day and age, the flowchart is provided in electronic format on the manufacturer's electronic service documentation, the material that they provide to dealerships. If that is the case, perhaps you could seek a printout (a PDF) from a European contact, or persuade a Mercedes dealer in Morocco to let you have a look at their on-line service manual for your vehicle.

In summary - I'm suggesting you now approach the problem by attempting to rule out problem causes, rather than by attempting to identify problem causes. Hopefully that approach will lead you to identifying the cause of the problem because the cause will be the only remaining source that you cannot rule out.

Michael

I apologize for the delay in response to this thread. Morocco started shutting down due to Covid-19 shortly after we received and installed a new rear wheel speed sensor. We got distracted with hunkering down in the desert during the State of Emergency / lockdown.

Below is my husbands write up on the issue.

If anyone is curious about our travels, our blog is:
Come, OverlandWithUs… – Ryan and LeeWhay's meandering adventures

Thanks again for all your input.

It's fixed! Ok, well, at least after 250 miles and ten or so on and off cycles.

The new right rear wheel sensor (906 905 09 01) that our friends brought from the US on Sunday ended up fixing the issue. No more dashboard lights, trouble codes, etc!

Thanks to Dennis for confirming the part number in Post #21 above and for the sequential ordering of likely issues in Post #7. Of course, it turned out that his #1 issue (failed sensor) was indeed the issue we had.

As a side note, I did swap the left and right rear sensors after slightly modifying the engine harness's left and right connectors (done previously). The Sprinter's computer did not protest and the raw wheel speed sensor data was consistent between all four wheels. This was a very short (several meter and a few minute) test - far from long-term tested. My conclusion is that the rear wheel speed sensors are interchangeable with slight connector modifications. I may buy a spare sensor (right of left) if we continue to use this overseas...

My conclusion after almost three weeks of making almost no "progress" on our trip is that the Sprinter is a fine first-world Overlanding vehicle. Getting the wheel speed sensor would have been pretty trivial in the US, Canada, and/or Europe (maybe Mexico?). It's pretty inexcusable to lose the following functionality (in rough order of importance) when using the Sprinter for third world country overlanding: 1) 4X4 (all wheel drive), 2) low-range, 3) traction control, and 4) cruise control.

The really disappointing part of this issue is still outlined in my Post #13. The sensor seemed to actually be working. I mean that it was correctly reporting the right rear wheel speed...

Thanks to all for the help! And, thanks, especially, to Dennis!

hello, there's a big new Merc dealer on the Casablanca road in to Marrakech , got back from a round trip to Gambia at the end of Feb, my 1989 ,208D never missed a beat, no sensors no problem. exhaust broke in half in Senegal ,but Zebra bar got me going, then again in Spain, but GumGum and jubilee clips got me home. good luck. regards chris

I guess with a modern 4x4 you should bring your own advanced OBD2 scanner to Africa?
One traveller had to abandon his fairly new Range Rover in Agadez only with electronic issues...
Related to this, a cousin of mine runs a garage in Chico, California, specializing in older cars Mercedes wont accept for repair - meaning those more than ten years old.
Some have what appears to be only minor faults, but can't be driven. Changing components identified as faulty by thé scanner sometimes doesn't help.
He said the industry standard for the harness connectors is they should hold up being taken apart and put together six times.
Six times. That's all.

Gratulation for solving the issue!

I did carry a Notebook with the Toyota Techstream software and USB Dongle with me, when I did the Transafrica and while travelling in south america.

Driving with an modern 4x4 in remote areas - could made that to a valuable gear.

I did just use it for resetting errors, what happens twice in Africa - not in south america. But if something would go wrong, I can phone to my european mechanic and try to solve or troubleshoot issues.

Getting spares abroad need extended time abroad, too if you ask a toyota mechanic. 60 Days fright, 40 days Express Airfright was named severall times. With Toyota many Parts are "on Stock" to be honest, but at sample an european model has severall stuff equipped what a car in Africa/south america dont have. (2nd Aircon, 2 batteries, same kind of diesel particle filter and so on..)



Here I wrote down my experiences, how to get spares abroad:

https://www.4x4tripping.com/2015/04/...weltreise.html

In my eyes everytime something can go wrong, but it rarely does. I wish you luck on your further trip - hoping that (c)ovid restrictions get solved!

Surfy

__________________
About Overlanding, Travelogues, Equipment
Trans-Africa over the west coast