Highway Breakdown (transmission issue?)

Just thought I’d report that I’m broken down on US 395 near CA-108 (Eastern Sierra in California), far from any town, while I await a tow of my 2016 Unity. I’m 90 miles from the nearest Mercedes service center in Reno which is apparently where I will be towed. (4:45 pm PST 6/4/2019)

What happened is I suddenly experienced multiple and ongoing jerking motions and then grinding, apparently from the transmission as it tried to jump between gears. I was able to pull off the highway – luckily there was a pull off area immediately ahead because the transmission was seriously not happy about continuing any further. After sitting a bit, I tried moving forward and backward a few yards but started getting the grinding noise and jerking motions in either direction. I also hear grinding noise from the front when braking, this all at very low speed.

With a web search, I see that it might be nice to check the transmission fluid level but there’s no built-in dipstick so I can’t do that. It’s only been like 500 miles since my last service (B).

Anyway, I called in to Mercedes roadside service and they’ve promised a callback from a tow service to get me to Reno. They don’t offer any troubleshooting over the phone. They do say that it may take quite a while given the distance and the type of vehicle (25 ft RV).
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Did you try switching to a lower gear?
As I described, the issue now occurs just trying to move forward or backward from where I am. So, there is no lower gear.

Still waiting for Mercedes to find someone within a few hundred miles that can handle this size of vehicle. First guy they contacted was told it was a Sprinter *van* not an RV built on a Sprinter chassis (as I had said on phone and via follow up text msg). Luckily, he didn’t drive the 85 miles to get here. (He called me to confirm and get photos.)

I’m now told they’re looking for a large wrecker that can come and drop the drive line so that it can be towed.

My two cats are not going to enjoy this experience!


2014 LTV Unity TB
Good luck - from where you are to Reno is not an easy tow. Curious to hear how this progresses/ends.
Well, it’s been about 2.5 hours, still no tow service found. Last I heard was a half hour ago they were still looking for one that could get here.

Meanwhile, I just tried driving forward and backward a bit and it would seem the transmission is working again, at least for the moment. Looking this up on the web, perhaps the transmission fluid had overheated (lots of mountain ascents and descents today). I never got an engine light or message though. I’m now wondering if I could limp up to Reno, taking it very easy along the way, even stopping often to let it cool. Dumping most of my fresh water now as I consider this. Would hate to get stuck somewhere where I can’t pull off the highway or with no cell reception though. (Particularly with the cats on board.)

Update: Well, I didn’t get a mile before getting a warning light (triangle with “!”) but no explanatory message.

Oh, wait, after a couple of minutes of sitting with engine off I get “Visit workshop and ESP and ABS”? Apparently this indicates that the “electronic brake force distribution” system (associated with the ABS system) is malfunctioning/ deactivated. Don’t know why this is coming up now after the transmission issue – lack of engine power for engine breaking?
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Mike DZ

2016 View 24V (2015 3500)
Well, it’s been about 2.5 hours, still no tow service found. Last I heard was a half hour ago they were still looking for one that could get here.
On the east coast it recently took me 7.5 hours to get towed 5 miles using MB roadside assistance.
Update: Round about 8:30 pm (about four hours have passed), I’m still waiting for the Mercedes roadside service to locate a tow service that is willing to come this far and can handle the vehicle. I had stopped again after going less than a mile when I got that warning light and messages I didn’t recognize but after looking them up I decided it was probably safe to try driving, just taking it slow and keeping it easy on the transmission and stopping if I start to hear noises or it acts up again. At the same time, I get a new text message that the original tow service that was assigned to me before they realized they couldn’t handle the RV is assigned to me again with an arrival estimate of three more hours. I send a message asking for confirmation that they can really handle the vehicle and decide to start driving. (And tell them so.)

They eventually get back to me (seems to take like 10 minutes) to say that they can’t assist me if I move the vehicle. Well, the transmission is holding up over 20 miles, nothing weird happening any more, so I cancel the tow request and continue on.

I’m now boondocking in Gardnerville, near an auto repair place that works on Mercedes. If they can’t address whatever the issue is tomorrow morning, I’ll continue on to Reno and the official Mercedes service center.


2015 RT SS Agile (3.0L)
Well, at least you're now near "civilization"! -- I got married just up the road (next to Lake Washoe) .... 44 years ago!


2016 Unity TB
FYI, I was on that same route a couple of weeks ago, had a fuel leak, and the M-B Reno folks did a good job to diagnose and repair the issue.

Bone Head

2014 LTV Unity MB
So sorry to hear of your dilemma.

First piece of advise: NEVER DUMP YOUR FRESH WATER! You don't know how long you are going to be "off line" and you can always dump later.



2018 Wonder FTB
And that 250 pounds isn't going to make any difference in the 10,000 pound scheme of things...

And I hope they are all still alive!
No worries about dumping the fresh water... I only brought it down to 20% (could go a long time with that much water) and I was traveling on busy US-395 anyway.

So, for the rest of the story:
As I described earlier, I was actually able to drive to Minden/Gardnerville after waiting for a couple of hours for Mercedes roadside service to try to find a tow truck. (I guess I'm glad they didn't.) I found a place to wait overnight for the European auto repair to open the next morning. Once they did open, they redirected me to a transmission place nearby that had a lift that could accommodate the Unity. That place scanned for codes first and found a few:
P10C700 Internal fault in component B90/2 left EKAS
P10C800 Internal fault in component B90/3 right EKAS
P126A00 Component M72/2 intake port shut off, actuator faulty
P162500 Water content in fuel has reached upper limit
D40C Right rear wheel rpm signal from traction system not available on can bus

They checked the transmission fluid level, color and smell. All good. They decided to clear the codes and take it for a test drive to see what would come back. Well, the codes did not return during the test drive and everything seemed to continue to function normally (as it had after I gave up on waiting for the tow for several hours). Best working theory was that the failure from the rear wheel rpm sensor interfered with the traction control and confused the transmission as to what gear to go to as well as engaged the ABS when I was braking while doing my super slow forward/backward test right after pulling over. (And also led to the warning from the ABS system.) The water content in fuel warning sounds like what happened when I got my Service B done some 500 miles or so ago. I remember being shown the water they kept pumping out of some part of the system. This transmission shop was not able to get additional details on what the other codes were about. They advised me to head up to the Mercedes service center in Reno, which I did.

On to Mercedes in Reno, during which time the check engine light came on. (I've had a spurious check engine light in the past that my local auto repair outfit was unable to diagnosis and last time I was at the Mercedes dealer for a recall, they didn't have time to take a look at it.) I had to wait a couple of hours before they could get to my Unity and then a couple more hours while they investigated (and test drove it). No issues (or problem codes) arose during their test drive either. They mentioned that they wish they were able to see the log on the codes that had been cleared so they could see the timestamps on them to see which corresponded to my incident but they understood why the other place tried clearing them to see if they'd come back.

End results:
The check engine light (P203b00) has a bulletin on it concerning issues with the reading of the DEF level. Level is good at this time. They suggested replacing connector pins and housing on the ad blue module at some point in time.
They were concerned about the codes relating to the turbo air intake actuators as this is very unusual to fail at merely 24,000 miles and very expensive to get at and replace. Their testing showed that the actuators were working now though and suggested waiting to see if this problem reoccured.
As for the rear wheel rpm sensor, they also thought that this might have been the cause of what I experienced and so, after checking that the wiring to the sensor was good (I've had mouse/rat issues already, including having to repair the wiring to the external temp sensor), they recommended I replace the wheel sensor. Which I had them do.

All told, only the wheel sensor was replaced. $600 for diagnosis/parts/labor at the dealership, $100 for diagnosis at the earlier shop. I've since been up and down various steep grades and continued back down where I was previously headed on US-395. So far so good. (Currently boondocked between Bridgeport and Mono Lake – and just discovered I forgot to pack the counterweight for my telescope. Dag gonnit!)

Oh, and, while I was waiting for my service at the dealership, my Nova Kool 6800 fridge stopped running. Couldn't do anything to get it going again as the fridge temp climbed up. I spent the following day pulling it out and troubleshooting it. Made a change that seems to have it working again but not ready to report on that yet. ;-)
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2015 RT SS Agile (3.0L)
...And the adventure continues.... Glad you're back on the road again, at least! Thanks very much for the detailed update!

I've always thought it's nice territory out there -- after our marriage ceremony at a Lake Washoe ranch, wife & I traveled all the way down 395 for honeymoon. Stopped at Devil's Postpile, a few other interesting places, ended up at sister's place on the beach in the LA area.... good memories.

Bone Head

2014 LTV Unity MB

I assume that you know from other posters, that the wheel speed sensor should be covered under the 5 year 100,000 mile emissions warranty?? This is a parts AND labor warranty!!


I assume that you know from other posters, that the wheel speed sensor should be covered under the 5 year 100,000 mile emissions warranty?? This is a parts AND labor warranty!!

Surely the wheel speed sensor should have been covered by your emissions warranty as others have previously reported?

Well, no actually. I was not aware of any previous discussion about the wheel speed sensor. Also, without my asking, the dealership said they checked whether the speed sensor would be covered under warranty and specifically said it was not. They did say that if the turbo air intake actuators fail that it would be covered and that it was otherwise a high cost repair.

I guess I can contact Mercedes to double-check the warranty on the speed sensor.


UK 2004 T1N 313CDi
I guess I can contact Mercedes to double-check the warranty on the speed sensor.
Stress 'EMISSIONS WARRANTY' and not general warranty to them.


PS Look in your handbook for the list of included items for your emissions warranty before calling.

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