The exact method used to locate and trigger the wheel speed
sensors is absolutely critical to the correct operation
of the Traction Control System. There are a number of different
ways to construct the pick-ups, the easiest being the bolt
detection method. The TC system needs a minimum of four
pulses per revolution, there is no maximum. There can be
a different number of pulses from front to rear, but not
between left and right across the same axle. Eg. 34 teeth
at the front and 4 teeth at the rear is fine, 34 left front
and 4 right front will not work.
The sensor works by detecting the presence of a ferrous
trigger point. Mount the sensor at a gap of 1mm from the
hub bolts / disc bolts. The head of the bolt must be flat,
a cap head will cause a double trigger as it picks up each
side of the head. Turn the hub slowly and check the gap
never grows bigger than 1mm from any of the bolts. The sensor
must be rigidly mounted so no large vibrations occur that
will move the sensor head more than 0.8mm away from the
reference points and the head must be at 90° to the surface.
If a sensing plate / disc is used, it must not be warped
or mounted at an angle that would cause the distance between
the head and disc to change by more than ±0.5mm. The material
used for the reference must be of a ferrous type, if in
doubt, check to see if it attracts a magnet. The reference
can be painted or plated.
