3 Diagnostics, Troubleshooting and Testing
29
Meritor WABCO Maintenance Manual MM-0112 (Revised 07-05)
Tire Size Range
ABS
For correct ABS/ATC operation with the standard ECU, front and rear
tire sizes must be within ± 14% of each other. When this tire size range
is exceeded without electronically modifying the ECU, the system
performance can be affected and the indicator lamp can illuminate.
Calculate the tire size with the following equation:
RPM — tire revolutions per mile
RSC
RSC requires that the steer axle tire size range be no more than 4%
of a pre-set value.
Call Meritor WABCO at 800-535-5560 if you plan a tire size range
greater than those specified.
Testing Components
CAUTION
When troubleshooting and testing the ABS system, do not
damage the connector terminals.
Voltage Check
Measure voltage at the pins indicated in Table F.
앫 Voltage must be between 9.5 and 14.0 volts.
앫 The ignition must be turned ON for this test.
Table F: Voltage Check Pins
NOTE: Pin locations are illustrated in Figure 3.23 (Frame) and
Figure 3.24 (Basic and Universal).
Figure 3.23
Figure 3.24
% Difference =
RPM Steer
RPM Drive
– 1 x 100
ECU Connector Pins
Universal 14-Pin 4 and 9
9 and 4
Basic 14-Pin 7 and 4
8 and 9
Frame-mounted X1-Grey 1 and 12
2 and 11
Figure 3.23
X2-BLACK
11 2
10 3
94
85
76
12 1
X1-GRAY
12 1
11 2
10 3
94
85
76
X3-GREEN
X4-BROWN
(ONLY FOR 6 CHANNEL)
12 1
11 2
10 3
94
85
76
11 2
10 3
94
85
76
12 1
VIEW INTO ECU CONNECTOR
1002052a
Figure 3.24
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
15
BASIC
UNIVERSAL
1
2
3
4
5
6
7
8
9
10
11
13
14
15
14
VIEW INTO ECU CONNECTOR
4004020a
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