Jim Grant's Tech Tips
'99 Chevy Silverado, ABS problem
Q:
My
‘99 Chevy Silverado pick-up’s ABS system does not work at low
speeds, approximately at 5mph or less. The result is an incredible shutter
in the vehicle and loss of braking. I have talked to several people who
have seen the same problem. The dealer says he can realign and clean everything
up but will not guaranty it will fix the problem.
-
Kevin M.
A:
It
doesn’t sound as if your ABS system isn’t working, it sounds
more like it’s working too much! My first suggestion is to have a
technician temporarily disable the ABS system and drive the vehicle. If
the brake operation returns to normal then an inspection of the wheel
speed sensors are in order. We’ve been seeing a speed sensor related
problem that will not set an ABS computer code or if a code is set it
is unrelated to the problem. Might I suggest this approach? Have the repair
facility connect a computer scan tool and monitor the wheel speed information
being reported by the ABS computer. What we’ve found is at about
5 to 6 MPH, if there is a wheel speed sensor problem, there will be a
sudden drop in speed at one or more of the wheels reported by the ABS
computer. The wheel speed sensor that shows the drop in speed when the
others don’t, is the suspect sensor. When the ABS computer sees the
reported drop in wheel speed and you step on the brake (even lightly)
the ABS system will become active and start relieving the brake pressure
to the wheel that it perceives as not turning. I don’t know about
that sensor realignment line your being fed. About all you can do with
the sensors on your vehicle is make sure they’re clean, free of bits
of metal on the magnet of the sensor and that they’re bolted in correctly.
More often than not the problem you’re having is the result of bad
information. A new wheel speed sensor may be the fix.
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