ABS sensor things to check

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Active Member
Jan 7, 2017
2005 S320 CDI
A couple of things I've learned over the years about ABS sensors and thought I would share.

One key driver of failure over time is rust, this can have two impacts.

1. if it's under the toothed pulse ring then the ring expands and can have 2 issues.
a) the ring expands and begins to rub on the face of the ABS sensor, this can also be made worse by general bearing wear allowing slight movement between the ring and the sensor face

The first symptom of a sensor failing from gradual wear of the face might be an ABS light coming on intermittently, finally it will be a hard fail as the wear cuts down to the active coil in the sensor.

If you pull the sensor from the mounting hole you can usually see wear on the active surface where it has impacted on the toothed wheel. If you pull the sensor and see wear one cheap fix is to create a thin card/thick paper gasket to create a slightly bigger gap when you fit the new sensor.

b). the toothed ring breaks and will need replacing, if the toothed ring has broken then replacing the sensor will not fix the problem but you may still see the wear symptom on the sensor tip. always look down the hole with the sensor removed and check for any breaks in the ring!

The other simple test is to measure the resistance at the under wing plug, most "dead" sensors show very high resistance, infinity or Mega ohms, good ones less that 2,000 ohms.

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