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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22907
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I am having problems with my Mercedes B170 W245 1955. Suddenly

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I am having problems with my Mercedes B170 W245 1955.
Suddenly and for no apparent reason the ABS
Run flat not available rear brake light warning ESP all come up on the dashboard and the car looses power only able to go up to 30mph.
Switching off and restarting clears all the malfunctions.
But they randomly all come back at once.
I tried resetting to factory settings but continues the problem from time to time.
Any ideas.

If the ABS light is staying on then this would indicate a fault with the system which shouldn't effect the regular braking performance so the car is still safe to drive.

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

However with ABS systems 99% of the time its a problem with one of the wheel speed sensors and I'd first check the connections at all four corners first for any signs of corrosion or chafed wiring.

The sensor is located in the wheel hub so you'll have to remove each wheel in turn to inspect them all.

Also check that the toothed wheel that the sensor points to is clean and free of any debris.

you can check each sensor's function by plugging the two output wires into an AC voltmeter and spinning the wheel quite quickly, you should get a voltage signal that increases with rev's.

Its possible that the fault is only a bad connection to one of the wheel sensors.

This may be remedied by removing each wheel in turn and unplugging each sensor and cleaning the contacts with a squirt of electrical contact cleaner. Then refitting.

Customer: replied 3 years ago.

would the bad connection account for all the faults including the rear brake light warning?

As they all disappear when I restart I do not think these are real faults.


the ABS / wheel speed sensors are used by all the faulty functions so as its the common thread I think its highly likley that a sensor or a bad connection to a sensor is the issue

I agree that its likely to be an electrical fault as these can be intermittant and effected by temperature
so try getting a fault code read off as it will save time in the long run
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