Fault Code Guide

4. Set a digital multimeter to the AC voltmeter
mode. Connect the probes to the cable connec-
tor terminals for the sensor being tested.
5. Rotate the wheel by hand at a speed of 30 rpm
(one-half revolution per second) and read the
voltage output. The wheel speed sensor must
generate a minimum of 0.2 volt AC.
• If the voltage is at least 0.2 volt AC, skip to
the next step.
• If the voltage reading is less than 0.2 volt
AC, push the sensor in its holder until the
sensor touches the tooth wheel. See Sub-
ject 120 for instructions. Repeat the volt-
age test.
• If the sensor output is still less than 0.2
volt AC, replace the sensor.
6. Install the connector on the ECU. Remove the
jack stands, lower the vehicle, and remove the
chocks from the tires.
Modulator Valve Tests
Modulator Valve Function Check
NOTE: Valves can be tested using the Meritor
WABCO PC Diagnostics software or the follow-
ing procedure.
Modulator valves control the air pressure to each af-
fected brake during an ABS function. To make sure
the modulator valves are working, listen to them
cycle during the ABS self-test.
1. Park the vehicle on a level surface, set the park-
ing brake, and shut down the engine. Chock the
rear tires.
2. Turn the ignition switch on.
3. When the ABS warning light comes on, listen for
the modulator valves to cycle one by one, then
together diagonally. See Fig. 2.
• 4-Channel valve cycle: 1, 2, 3, 4; then 1
and 2 together followed by 3 and 4.
• 6-Channel valve cycle: 1, 2, 3, 4, 5, 6;
then 1, 2, and 3 together followed by 4, 5,
and 6.
4. If the valves do not all cycle correctly, turn the
ignition off and check the connectors for tight-
ness. Repeat the self-test.
5. If the valves still do not cycle correctly, start the
engine and check the air line connections to the
valves for leaks. Shut down the engine and
tighten the air line fittings. Repeat the self-test.
6. If the valves still do not cycle correctly, check for
fault codes. Perform the next test, "Modulator
Valve and Cable Resistance."
Modulator Valve and Cable
Resistance
To check the resistance in a modulator valve and
cable circuit, perform the following test:
1. Park the vehicle on a level surface, set the park-
ing brake, and shut down the engine. Chock the
rear tires.
2. Disconnect the modulator valve connector from
the ABS ECU. See Table 1.
3. Connect ohmmeter probes to the cable connec-
tor pins for the modulator valve "In" solenoid and
"Ground." Read the resistance. Then, move the
probes to the "Out" and "Ground" pins and read
the resistance.
1
2
3
4
A
B
f421562
04/09/97
NOTE: During the self-test, the valves cycle one by one
in order (1–2–3–4), then in pairs diagonally (1/2 and
3/4). A 4-channel valve cycle is shown.
A. Cab B. Curbside
1. Right Front Modulator Valve
2. Left Rear Modulator Valve
3. Left Front Modulator Valve
4. Right Rear Modulator Valve
Fig. 2, Modulator Valve Self-Test Sequence
Meritor WABCO Pneumatic Antilock Braking System
(ABS)
42.00
Testing
Business Class M2 Workshop Manual, Supplement 0, January 2002170/4