Wet Motor Speed Sensor

[ayedurand]

I've recently taken delivery of a 2015 red B250e and had it over to the Mercedes-Benz dealership for inspection. While they have no idea how to work on this car (I live in Minnesota) I did instruct them to pull the motor speed sensor and inspect for water. They found water at 31,811 miles.

I'm working with Vroom to make it right but I expect that it'll be going back to them.

Vehicle VIN = WDDVP9AB9FJ006734

I've been doing a lot of research on this and I suspect that the issue is a design defect and is to be expected on the majority of these cars. With the exception of one car I've seen in my search for a car the duty cycle is relatively low. I wish I had known about this prior to making the purchase.

*I have pictures of the sensor if anyone would like to look at what I found but it is very similar to the middle sensor at the end of the QC Charge video.

https://www.youtube.com/watch?v=txD7u2DKanE

The car is otherwise perfect. Really disappointing.

 

[PaulShin]

What does the wet speed sensor mean for the car?

 

[Smooth]

What does the wet speed sensor mean for the car?

Hi Paul, there is coolant that circulates inside the car's drive unit. The DU is made by Tesla and a similar unit was also used in the 2012-14 Toyota RAV4 EV and some early model years of the Model S. Over time, an internal leak can develop and coolant can get into places where it doesn't belong. This has the potential to destroy electronics and render the entire drive unit inoperable. If this happens, the unit typically has to be completely replaced; it is a time-consuming and extremely expensive (usually over $10K at the dealer) repair. Checking the speed sensor is the most convenient way to see if this has started happening since it's relatively easy to access, which is why people recommend looking at it periodically. Some cars also start making unusual noises if the drive unit begins to fail.

I know this sounds scary since there is really not much you can do to prevent it, but not every vehicle is affected and many people have no issues. Anecdotally, it seems to occur more often in the earlier model years of the B-Class.

 

[hyap463]

For cars that are still good, would periodic replacement of the coolant gaskets plus checking the speed sensor prevent the drive motor failure?

 

[PaulShin]

What does the wet speed sensor mean for the car?

Hi Paul, there is coolant that circulates inside the car's drive unit. The DU is made by Tesla and a similar unit was also used in the 2012-14 Toyota RAV4 EV and some early model years of the Model S. Over time, an internal leak can develop and coolant can get into places where it doesn't belong. This has the potential to destroy electronics and render the entire drive unit inoperable. If this happens, the unit typically has to be completely replaced; it is a time-consuming and extremely expensive (usually over $10K at the dealer) repair. Checking the speed sensor is the most convenient way to see if this has started happening since it's relatively easy to access, which is why people recommend looking at it periodically. Some cars also start making unusual noises if the drive unit begins to fail.

I know this sounds scary since there is really not much you can do to prevent it, but not every vehicle is affected and many people have no issues. Anecdotally, it seems to occur more often in the earlier model years of the B-Class.

Thank you for sharing! I checked mine over the weekend and there is a little bit of fluid on the sensor. Is this something I (a regular user) could replace?