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Old 08-08-2018, 07:47 AM   #1
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Rear wheel speed sensor fix

As many of you have experienced, we had a rear wheel speed sensor fail last fall on a long trip away. The three symbols on the dash indicate no abs, traction control and cruise is inoperable.

I used my Autel 619 to check for codes but none showed up.

Our dealer, Star Motors here in Ottawa (a terrific store I might add!), diagnosed a right rear speed sensor and replaced it. $700 later it's all good.

Fast forward to this past weekend on a trip to La Malbaie just east of Quebec City, and at a gas stop, on starting the trio appear once again! Boo.

I finished the trip without cruise and on arriving home read lots on sprinter-source about how the sensors can become fouled and give inaccurate readings. So I crawled under the rig and removed the sensors from the rear hub. It was much easier than I expected! Initially I removed the duallies, only to learn that wasn't necessary. There is a 8mm torx nut on the rear of the hub that holds the sensor in place, accessible freely. So I removed the zip ties and the sensor and the right was grungy, not so the left.

I reinstalled and drive the rig, with no change. Boo.

I called our service advisor, and found the tech at Star Motors was on holiday till next week. So I ordered the left side, figuring that if the right was replaced, it must be the left! And if I was wrong they would warranty the right side. I also asked if a reset of the ECU would be necessary and Martin (our advisor) said no, "they should be plg and play".

That got me thinking about computers...so I unplugged the sensor connections from the canbus on the cross member just ahead of the rear axle. They are supposed to be weatherproof, but we all know about the nature of the Curt rear signal controller! There was a fair amount of dirt around the connection, but internally looked ok. Interestingly the left and right connections are different!

I reconnected and started, and drive off and the lights went away! Woohoo!

Maybe they'll come back on, or maybe the connection was just slightly loose? But I have my cruise back and more knowledge about how these things work.. The first photo is the Torx socket, the second the back of the hub and the third the sensor connections on the rear face of the cross member.Click image for larger version

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Old 08-08-2018, 08:32 AM   #2
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Good info!
I have had the warning lights come on/no cruise after having hit a bumpy road area. This was in my previous rig on a 2013 chassis. However, if I turned off the engine for a few minutes it would reset. Have not had this happen yet on my 2015 chassis.
My brother has a 2014 3/4 ton Dodge Ram truck and his does the same thing.
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Old 08-08-2018, 03:20 PM   #3
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Unfortunately, after a couple of kilometres, and a speed bump, the lights came back on...so much for the quick fix. I'll buy the new speed sensor and install tomorrow.
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Old 08-09-2018, 05:06 AM   #4
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Thanks for the info. Both of my rear sensors failed over time but were replaced on warranty. Now that I am "out of warranty " I wondered if those sensors are plug and play since they can be purchased for $100 to 130. My autel was able to tell which sensor. Good luck.
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Old 08-09-2018, 08:07 PM   #5
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Well, after $232 ($20 US, grin) for the sensor and Ĺ hr under the rig, she's fixed. I took it out for a spin and over some bumps and we're all good. Plug and play indeed!
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Old 08-12-2018, 05:28 PM   #6
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Not sure if it's the same problem...

Near the end of a 250 mile trip a week ago I left a traffic light and my MBS started bucking and surging like something was bad wrong and those 3 lights were on also. I pulled into a diesel station to fill up and applied the park brake like I always do. When leaving, I released the park brake and could tell the rear brakes were still on. I applied it again and released it and all was good and the 3 lights went away. Upon arriving home 250 miles later, the 3 lights came back on. I backed into the driveway, shut it down, came back out a while later to finish backing up and the lights were gone. I tend to think my issue is related to the parking brake not releasing entirely. Has anyone else experienced this?
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Old 08-12-2018, 05:47 PM   #7
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I had a '99 Dodge Dakota with a magnetic pickup on the driveshaft that came off 3 times. Each time the magnet came off I lost the speedometer and anti-lock brakes, it didn't have traction control because of having just 1 sensor for the rear wheels. I was familiar enough to use the tachometer to determine the speed.
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Old 08-15-2018, 04:59 PM   #8
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Just back from M-B dealer with a new sensor under warranty.

Brought our rig home this afternoon. The Service manager for the Sprinters mentioned as I was leaving that they see a lot of rear wheel sensors on RV's, not the regular Sprinter vans, go bad for some reason. He did not know why, guessed perhaps braking heat from the extra weight.

Mine chose to act up in Custer State Park in South Dakota causing us to abort a western road trip (4th of July holiday week) and head home to New Jersey. The error lights cleared after about 5 or 6 hours driving over two days. Being a late Saturday afternoon initially, and in SD, left us with zero Mercedes Benz warranty service options nearby. The one dealership was in the far southeastern corner of the state in Sioux Falls. Lights cleared and cruise functionality returned about halfway there. We just went home after that as we were not sure of the reliability.

Mine was behind the right rear wheels. Nice to know about chassis rail connectors and 8mm Torx sensor removal. Only thing was this incident happened on a twisty but slow road in the state park, and that was after an earlier (~hour) long stop/go delay of about hour for a buffalo herd crossing. So maybe was heat?

So ??? I'm not happy with just ~11500 miles on the odometer!!!

Oh yeah, warranty stuff (also a NOx sensor behind the catalytic convertor) was free, but oil change and fuel filter service (10K miles) left an $800 hole in the bank account!
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Old 08-16-2018, 09:02 PM   #9
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one more thing maybe... RR sensor baked?

The exhaust pipe is in the right rear wheel well are too!!!

My exhaust pipe has melted the mud flap when it was blown back under highway speeds wind load... so lots of toasty heat in the vicinity!
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Old 08-17-2018, 08:13 AM   #10
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Should be...

The exhaust pipe is in the right rear wheel well area, too!!!
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