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Matt, Engineer
Category: Mercedes
Satisfied Customers: 21870
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I he a abs light and esp triangle light on and brake keeps

This answer was rated:

Hi, I he a abs light and esp triangle light on and brake keeps on jamming on one wheel. It's ml350, 2010
JA: Has the light been on for some time?
Customer: Yes
JA: Are you fixing your ML350 yourself? What have you tried so far?
Customer: Tried nothing, I hv a mechanic friend who can do this job
JA: Anything else you want the mechanic to know before I connect you?
Customer: No


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.

he dash / ignition lights are on then this usually means that its off

If this is all OK then its possible the car needs a new starter motor

Customer: replied 11 months ago.
My esp light is also staying on in a yellow triangle with abs light. As I told you sometimes it goes off and the car runs perfectly and sometimes both the light stays on and still the car runs ok without being randomly braked.


thanks for the extra information

the ESP and ABS systems both use the same wheel speed sensors so this does point to one of them being at fault

if you don't have access to a scan tool then I'd suggest to use a voltmeter as I've suggested to check over each of the wheel speed sensors at the socket

Customer: replied 11 months ago.
I found the scanner guy . It shows that the rear left sensor is not working. Shall I replace it ?


good work, I'd 1st check the condition of the sensor connection thats tucked up under the plastic wheelarch liner if thats clean and dry then yes replace the sensor

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