Pesky Sierra Cosworth ABS fault
Discussion
Can anyone assist with a Cossy ABS fault that's proving difficult to fix ?
Symptoms are ABS light comes on and extinguishes as expected when engine is started. As soon as you start to move, ABS light comes back on. ABS doesn't work.
Have checked at the ABS ECU for waveforms from each wheel sensor, all four are present, impedance across each sensor is the same few ohms. Have swapped ECU, albeit with a used one, and same fault persists.
If you jack up the back wheels and put in gear, light doesn't come on.
Sensors look OK, and hub reluctor rings are in place, no teeth missing etc..
Ford workshop manual is of no use, no diagnostics info. We're all now a bit stumped. Does anyone have any suggestions or advice ?
All help much appreciated.
Symptoms are ABS light comes on and extinguishes as expected when engine is started. As soon as you start to move, ABS light comes back on. ABS doesn't work.
Have checked at the ABS ECU for waveforms from each wheel sensor, all four are present, impedance across each sensor is the same few ohms. Have swapped ECU, albeit with a used one, and same fault persists.
If you jack up the back wheels and put in gear, light doesn't come on.
Sensors look OK, and hub reluctor rings are in place, no teeth missing etc..
Ford workshop manual is of no use, no diagnostics info. We're all now a bit stumped. Does anyone have any suggestions or advice ?
All help much appreciated.
stevieturbo said:
Waveform is present.
But are all the waveforms sensible and consistent ?
Can you put the car in the air and spin one wheel at a time, to determine if one single wheel might be activating the light ?
Measured the waveforms with an oscilloscope. All looked regular. When rear jacked up and wheels spinning both side gave same voltage. Tricky to measure amplitude and compare on the fronts however as spinning them by hand. Did see a Ford forum post with similar issue. He spun wheels at 60RPM and measured amplitude. Tiny difference pointed to faulty sensor. Time to buy a new sensor and try substitution.But are all the waveforms sensible and consistent ?
Can you put the car in the air and spin one wheel at a time, to determine if one single wheel might be activating the light ?
WhatIsIt said:
Could it be a worn wheel bearing causing the sensor ring to move closer/further from the sensor and upsetting the reading?
If the sensor rings are dirty they can cause trouble (apparently) but then I suppose you would see it all the time,- jacked up or not.
You may have to try substituting one sensor at a time for a known good one to eliminate them. The front's are the same from side to side (as are the rear's) but the front and rear's are different to each other.
Alternatively, could it be a loose connection somewhere completely different, that only shows up when the car moves (due to vibration etc). I believe the valve block electrical connector can be temperamental.
From what I have read, the ABS is only activated when you go above a certain speed (15 MPH or something like that) so maybe by just jacking the back up and the front wheels not moving, it may not be activating?
Have you looked on the various Ford forums? The Sierra ABS system is very similar to the Cosworth so those guys might be able to help. I can recommend www.xrstyle.co.uk
Thanks for the ideas, no play in wheel bearings, but since searched more and found reports of greasy rings causing this issue. Next step is to get a new sensor, clean out the rings and substitute it on each front side.If the sensor rings are dirty they can cause trouble (apparently) but then I suppose you would see it all the time,- jacked up or not.
You may have to try substituting one sensor at a time for a known good one to eliminate them. The front's are the same from side to side (as are the rear's) but the front and rear's are different to each other.
Alternatively, could it be a loose connection somewhere completely different, that only shows up when the car moves (due to vibration etc). I believe the valve block electrical connector can be temperamental.
From what I have read, the ABS is only activated when you go above a certain speed (15 MPH or something like that) so maybe by just jacking the back up and the front wheels not moving, it may not be activating?
Have you looked on the various Ford forums? The Sierra ABS system is very similar to the Cosworth so those guys might be able to help. I can recommend www.xrstyle.co.uk
There is a lower speed limit that triggers this. I can crawl in 1st at idle and it will never come on, however I've had the back jacked up and rears spinning at 30MPH+ to make sure I'm in the zone.
More searches seem to show up issues with the fronts more than the backs. I can't spin the fronts fast enough to get above this limit, so new sensor substitution is the next step. All wiring is solid, I've check continuity whilst pulling cables, etc.
catfood12 said:
Measured the waveforms with an oscilloscope. All looked regular. When rear jacked up and wheels spinning both side gave same voltage. Tricky to measure amplitude and compare on the fronts however as spinning them by hand. Did see a Ford forum post with similar issue. He spun wheels at 60RPM and measured amplitude. Tiny difference pointed to faulty sensor. Time to buy a new sensor and try substitution.
Amplitude wont be the issue though, unless it fell very low.The regularity of the waveform would be vital though. Any ecu reading the signal will clip the voltage anyway as voltage would get too high
When testing though,one wheel at a time. Does the light come on immediately wit each wheel, did one take longer etc ? That might help point you as to which one is the problem
Not specific, but this guy makes great diagnostic videos.
http://www.youtube.com/watch?v=bPdPhGcZOe0
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