ABS/Traction Control woes...
Discussion
A while ago I was just driving along and the dashboard pipes up saying ABS Fault and switches itself off and takes the TC with it. I pull over and stop and cycle the ignition and that seems to reset it.
Since then, the fault has occured a couple of times, However, the last time it would not reset.
So, I call our friendly colourful dealer in the south-east who very efficiently replace the ABS sensors.
Driving home tonight, ping.... ABS Fault..... Phone dealer who said they would see what they could find out..
Anyway, to help them out I was wondering if anyone had any ideas..
Since then, the fault has occured a couple of times, However, the last time it would not reset.
So, I call our friendly colourful dealer in the south-east who very efficiently replace the ABS sensors.
Driving home tonight, ping.... ABS Fault..... Phone dealer who said they would see what they could find out..
Anyway, to help them out I was wondering if anyone had any ideas..
Most ABS systems will do a function test not long after you begin driving. That is, the motor and valves on the ABS block will be cycled to check they operate correctly. In some cars, and if you are listening for it, you can hear the ABS motor kick in for a second or two when this happens. If this test is not successful, then this usually results in an ABS error and lack of ABS or traction control operation. It's very common in the Volvo 850/V70 series, along with hairline cracks developing in the ABS controller circuit board as time goes on (although this is around 10 years or so!). Another cause of this in these cars is a dodgy earth crimp connection to the fusebox where the ABS fuse is located, or a worn/dodgy ignition barrel in the steering column. I actually had this happen a couple of weeks ago on my V70R, partly because I have a pocketful of keys on my keyring which isn't too good for the barrel and partly because I have a tendancy to knock the whole lot with my knee while driving. Generally, if no error codes are stored or it re-sets between driving cycles, it isn't the wheel sensors, and in practise these are very robust in most makes of car. Hope this helps some! 
My brother had very similar symptoms on his 740i Sport. Car would be fine when started and at some point whilst driving the ABS would fail. It used to fail if he provoked the traction control to kick-in. A stop and restart fixed it in the beginning but it got worse and worse. We thought it was a sensor too but it turned out the ABS module itself was failing and had to be replaced for a not inconsiderable sum of money. Saying that the car was 7 years old with 85k on the clock (and I thought it was shocking the ABS module had gone so early). Hopefully that's not what you've got and it's something more simple.
stevieturbo said:
Most ABS systems self diagnose when hooked up to the scanner.
So it could be as simple as a wheel speed sensor....well, hopefully..
So it could be as simple as a wheel speed sensor....well, hopefully..
Yes, but if a permanent fault occurs this results in a stored code and the light on the dash on permanently. My money's on the ABS controller.
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