Speed sensor fault
05-23-2020, 01:38 PM
#1
Member
Thread Starter
Speed sensor fault
Couldn't get any help over on the coupe forums, so I'll try it here. I've got a 2013 E550 with Mickey Thompson drag radials. I ended up purchasing TEMA4x4 Coil Spring Spacers to lift the rear end up a little bit, so I could get better clearance. Mechanic shop installed them for me, and it was seemingly fine. Drove the car about 20 minutes home, and near the end of my drive the speedometer falls to zero, steering wheel gets tight, blind spot and lane assist unavailable, transmission barely shifts, very little gas and check engine light. Basically limp mode. Restarted the car and it runs fine for a few minutes, then same thing. Ran the codes and got all four speed sensor malfunctions as well as "Control unit malfunction" or something like that, can't remember that last one exactly. Took it back to the shop and called around, and pretty much came to the conclusion that lift spacer was confusing the air suspension and that's why it did it. Unfortunately, taking the spring spacers did not help. Does anyone have a clue what is going on with the car?
05-23-2020, 01:48 PM
#3
Member
Thread Starter
05-23-2020, 02:10 PM
#5
Member
Thread Starter
did some digging, and I know what that is now. I actually saw that sensor when it was back on the lift trying to figure out what was wrong. I will double check to make sure it is intact next time I look at it, but it looked fine. Is there anything else that it could be? Thanks
05-30-2020, 02:00 PM
#6
Member
Thread Starter
Alright, so followup: After the coil spacers were taken off and didn't help, we put the stock wheels back on. Car is fine. I don't understand how changing a damn tire completely kills this car. I ran the 19's for a week with no problems. I haven't done the fronts yet, so I've been running the stock 18's with the 19's in the back. Does anyone know why it is acting up now?
The only thing I can think of is that the coil spring spacers messed up the ride height slightly, and the 19's no longer work but stock still do. Is there a way to re calibrate ride height?
The only thing I can think of is that the coil spring spacers messed up the ride height slightly, and the 19's no longer work but stock still do. Is there a way to re calibrate ride height?
05-30-2020, 03:41 PM
#7
Super Member
First thing is first..... when the problem happens you need to read faults in all modules. Process all faults to see why it is doing it...... Proper diagnosis is required in this situation.
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05-31-2020, 11:23 AM
#8
MBWorld Fanatic!
Alright, so followup: After the coil spacers were taken off and didn't help, we put the stock wheels back on. Car is fine. I don't understand how changing a damn tire completely kills this car. I ran the 19's for a week with no problems. I haven't done the fronts yet, so I've been running the stock 18's with the 19's in the back. Does anyone know why it is acting up now?
The only thing I can think of is that the coil spring spacers messed up the ride height slightly, and the 19's no longer work but stock still do. Is there a way to re calibrate ride height?
The only thing I can think of is that the coil spring spacers messed up the ride height slightly, and the 19's no longer work but stock still do. Is there a way to re calibrate ride height?
05-31-2020, 02:48 PM
#9
Member
Thread Starter
What size are your rear tires on 19" rims? Just thinking if they are a lot bigger or smaller than the front there could be speed difference between front and rear wheels that the system in car could take as speed sensor failure if MB built some kind of speed difference limit in the system. I don';t know, but could be worth looking into...
Sounds partially correct.
Most OEM wheel / tires come out close to 26" rolling diameter so 3% would be about .78 inches, right in the range most "experts" thought you might get enough difference to trigger traction control.
BUT you can vary front AND back as much as you like without ABS problems, you'll just throw off the speedometer and possibly rub. It is DIFFERENCE in rolling dia. between front and back that you have to worry about as far as ABS / traction control. It only looks at the speed each wheel is turning and compares them to each other. I don't think it knows or cares what speed the wheel is turning versus any assumed OEM size tire or wheel?
Most OEM wheel / tires come out close to 26" rolling diameter so 3% would be about .78 inches, right in the range most "experts" thought you might get enough difference to trigger traction control.
BUT you can vary front AND back as much as you like without ABS problems, you'll just throw off the speedometer and possibly rub. It is DIFFERENCE in rolling dia. between front and back that you have to worry about as far as ABS / traction control. It only looks at the speed each wheel is turning and compares them to each other. I don't think it knows or cares what speed the wheel is turning versus any assumed OEM size tire or wheel?
So, my rear tires are 285/35/19. Assuming that this rule is correct, and I believe that it is, I need 235/40/19 in the front in order to be under a 3% difference in front and rear.
With that being said, I guess it was just dumb luck that I was able to run the fronts for a week with no speed sensor problem. Will update when new front tires get in.
F: 8.5 ET30
R: 9.5 ET45
