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w246 Left/right front ABS sensor diagnosis( and possibly solution)

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w246 Left/right front ABS sensor diagnosis( and possibly solution)

 
Old 01-19-2019, 12:48 AM
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w246 Left/right front ABS sensor diagnosis( and possibly solution)

My w 246 has the following errors
1. ABS deactived
2. ESP deactivated
3. Run flat indicator off
4. Check engine light
Hooked a diagnosis tool and got a lot of codes, but most point to the front right wheel speed/ABS sensor. The sensor affects a lot of things such as shifting( in automatics DCT).
At first the erros came on and off. When they were on, the vehicle was fine except that the brakes shuddered when used: the abs activated unnecessarily.
When the errors are on, the car feels stiff and steering is harder.
The problem could be on three things
1. The ABS sensor
2. The wire harness
3 The ABS ring in the wheel.
I think and hope it is the sensor that is bad since the errors were popping on and off.
I will try testing whether the sensor is bad and give my results later on.
I will try the following
1. Swapping the left(good) and right (bad) sensor and checking whether the error coes have changes. I will swap them , clear the codes drive a bit and check again. This should tell me whether the sensor is bad right away. But the sensors are a pain to remove: there is a video about the rear sensors but for the front you have to remove the wheel arch and underside cladding to access the connections. I will to other test to get data that might help someone else in the future. The sensor of the B class is the same as A class, GLA, CLA so the values should be useful for those cars too.

2. Check the resistance of the good and bad sensor and compare.

3. Check the voltages from the wire harness tp test whether the harness is the problem: the sensor should be a hall effect one. The good harness should have a power line around 12V and a signal line with a very low voltage with ignition on. I will compare both sides and see. i will be careful not to touch the two leads together(it might damage the ECU).

4. Measure the signal voltage from the sensor while turning the wheel with my hands and with ignition on. The signal is digital so it is either high or low and should be regular. A scope should be better for this but i dont have one

I will post and update with the values and my results. I hope it is just the sensor.
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Old 01-19-2019, 12:54 AM
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Old 01-19-2019, 12:08 PM
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The data I got from measuring the resistance of the sensors:
the right(bad) one : 1530 Ohms
the left (good) one: no resistance/open circuit.

The wire harness:
left
POwer wire: 11.52 Volt
Signal wire: 3 mV
Right
POwer: 11.52
signal wire: 3mV

I could not measure the signal voltage while turning the wheel

This means that the wire harness is good. The good one had no resistance/infinite resistance and the bad one had a resistance , which probably indicates a short in the sensor. So I will replace the sensor and it should fix the problem.

Last edited by zaakir ketwaroo; 01-22-2019 at 10:43 AM.
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