Fault Code Guide

6. Turn the ignition switch off.
7. If the voltage at the ECU is not within the speci-
fied range, check the battery voltage and test the
wiring to the ECU and to ground.
8. Connect the X1 connector to the ECU and re-
move the chocks from the tires.
ABS Pneumatic System Test
To check for air leaks in the ABS pneumatic system,
listen for the sound of escaping air at each valve. To
confirm a slow air leak, apply a soap-and-water solu-
tion to air line fittings and watch for bubbles.
Wheel Speed Sensor Tests
Wheel Speed Sensor and Circuit
Resistance
To check the resistance in a wheel speed sensor cir-
cuit, 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 sensor cable connector from the
ABS ECU. See Table 1.
ABS/ATC Circuit Pin and Wire Numbers
Pin
Connector
Pin
Number
Wire
Number
Circuit Description
X1
Gray
1 376C ECU Ignition Supply
2 376C ECU #2 Positive 12 Volt Supply
3 376T Wheel Spin Light and ATC Switch
4 1587+ J1587+
5 376R Retarder Interrupt Signal
6 1922-/1939- J1922–/1939–
7 1922+/1939+ J1922+/1939+
9 1587 J1587–
10 376L ABS Light
11 XGRD ECU Ground
12 XGRD ECU Ground
X2
Black
1 — Not used
2 378LFI Left Front Modulator Valve, In
3 378RF0 Right Front Modulator Valve, Out
4 378RFI Right Front Modulator Valve, In
5 377RF+ Right Front Sensor, High
6 377RF– Right Front Sensor, Low
7 377LF– Left Front Sensor, Low
8 377LF+ Left Front Sensor, High
9 378RF– Right Front Modulator Valve, Ground
10 378LF0 Left Front Modulator Valve, Out
11 378LF– Left Front Modulator Valve, Ground
12 — Not used
Meritor WABCO Pneumatic Antilock Braking System
(ABS)
42.00
Testing
Business Class M2 Workshop Manual, Supplement 0, January 2002170/2