23
Troubleshooting and Testing
4.6
Standard Testing
4.6.1
System Requirement
Tire Size Range
For correct hydraulic ABS operation, front and rear tire sizes must be within 8% of each other.
Contact the WABCO Customer Care Center at 855-228-3203 if you plan a tire size difference greater
than 8%.
Calculate the tire size with the following equation:
% Difference =
((RPM Steer/RPM Drive) – 1) x 100
RPM = tire revolutions per mile
CAUTION
When troubleshooting or testing the ABS, do not damage the connector terminals. Damaged
connector terminals may cause system malfunction.
4.7
Component Testing
4.7.1
ABS and ATC Warning Lamp
If the ABS and ATC warning lamps do not come on after the ignition is turned on, or come on but do not go
out after three seconds, check all ABS fuses. See the “System Diagnostics” section of this manual to check
lamp function using TOOLBOX™ Software.
Not all vehicles are equipped with an ATC lamp. See the vehicle manufacturer’s manual for
more information.
4.7.2
Wheel Speed Sensor Adjustment
On steering axles, the sensor is typically accessible on the in-board side of the steering knuckle.
On drive axles, the sensor is typically accessible on the in-board side of the rear axle spindle.
To adjust the sensor, push the sensor in until it contacts the tooth wheel.
Do not pry or push sensors with sharp objects.
Sensors will self-adjust during wheel rotation.
See the “System Diagnostics” section of this manual to check the wheel speed sensor air gap condition
using TOOLBOX™ Software.
No sensor gap is allowable at installation. During normal operation, a gap of up to 0.028-inch
(0.7 mm) is allowable.
