TM 9-2320-302-20
0013 00-21
ANTI-LOCK BRAKE SYSTEM TROUBLESHOOTING AND TESTING - CONTINUED
0013 00
TIRE SIZE RANGE
1.
For proper ABS operation with the standard ECU, front and rear tire sizes must be within ±14% of each other. When tire
size range is exceeded without electronically modifying ECU, system performance can be affected and warning lamp
can illuminate.
2.
Call Rockwell WABCO at 1-800-535-5560 if you plan a tire size difference greater than 14%. Calculate tire size with
the following equation:
% Difference = {RPM Steer divided by RPM Drive minus 1} x 100 (in this equation RPM means tire revolutions per
mile)
ABS MODULATOR VALVE TEST
1.
Measure the resistance across each valve solenoid coil terminal and ground on the ABS valve to ensure 4.0 to 8.0 ohms
(Figure 30).
1.
Ground Terminal
2.
Solenoid
Figure 30. ABS Modulator Valve.
2.
If resistance is greater than 8.0 ohms, clean electrical contacts in solenoid. Check resistance again.
3.
To check cable and ABS valve as one unit, measure resistance across the pins on ECU connector of harness. Check wir-
ing diagrams of system being tested (Figures 31 through 34).
