ABS sensor diagnostics

[Eugene Sokolovski <esokolov@worldnet.att.net>]

Jeffrey,

  I had a very same problem with my recently purchased 5kcstq
(the ABS light was coming on after a few minutes of driving), so here is
my BTDT. I am 99% sure  that one or more ABS sensors are not properly
re-seated when you had the suspension work done and that dealer is trying
screw you. The replacement of the ABS sensor caps (P/N 437 927 809 -$3)
is mandatory, and I bet they didn't do it.  You can actually test sensors if you

have a good digital multimeter. Jack up the car, put it on the 4 jack stands,
remove
the wheels and disconnect the ABS sensor connectors.Two of them are in the
engine compartment and two are under the back seat. Check their resistance
first-
it should read around 1k Ohm. Then start the engine, shift  the transmission
on the second gear and check the output voltage from each sensor while wheel
hubs are spinning. Or you can check one corner after another the same
way, but make sure that the diifferential locks are OFF.
  The DMM should be switched to AC voltage mode, 0-1 or 0-10V range.
I used FLUKE DMM and  the voltage readings from the sensors were around
100 mV-2V. If the reading is 0 then sensor is kaput or it sits too far from the
driveshaft spline. The sensor output voltage is very sensitive to the air
gap between the spline and sensor itself (that's what caps are for), and you can

actually adjust it by moving the sensor a little bit and see how the output
changes.  I adjusted mine so the output voltage is 700-800 mV at all 4 corners.
After that ABS works like a charm, just had a chance to test it during
yesteday's
snow storm around DC.

HTH

Eugene

'87 5kcstq  148K miles
1.8 bar, PowerDisk's, Euro's, still need some suspension work to be done ....





Jeffrey Mudrick wrote:

> I had the local shop (mistake #1) install new Eibachs and tires on my '87
> 5000csq; they lower the car nicely, and I'm happy enough with them. Problem
> is my "ABS off" light now comes on after a few minutes of driving. Punching
> the switch will shut it off again, but just for a few mintutes.  The local
> dealer (not terribly trustworthy in my experience) says I should replace
> both front ABS sensors at $150+labor each side.  It seems to me a remarkable
> coincidence that the light comes on only after the tire shop got their hands
> on the car.
>
> Anyone have problems/thoughts about these ABS sensors?
>
> Thanks.
>
>        Jeff
> '87 5kcsq
> 130k
> Eibachs
> lousy 1.3 bar