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300TDi ABS / Vacuum pump testing?


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My 300TDi ABS light has come on a few times recently and i have also noticed a general degradation in brake performance over the past few months, although the vehicle did pass its MOT back in March ok.

Reading the various forums it looks like i either have a genuine ABS problem like a sensor on its way out, or the vacuum pump maybe losing its efficiency. How can i test the ABS sensors and how can i tell or measure if the vacuum pump wants replacing?



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Guest diesel_jim

If it's the ABS light coming on, i'd imagine that it is a loose wheel bearing (as that is where the ABS sensor takes it's reading from.... from the edge of the CV joint or in the hub)

try jacking up each corner and grab the wheel at the 12:00 position and the 06:00 position, give it a wiggle. if it moves then you'll have a loose/knackered bearing.

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the sensors can be had for £60 each rather than the L/R £110+

the sensors read the ring on the CV and can get knocked back if the swivel pin bearings are worn/have play in them.

to check the vacum pump pull the connection out of the servo and start the engine place your thumb over the end and check to see if it is sucking, when you pull the connection from the servo if you hear the air being let in I'd suggest the Vac pump is fine.

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