Fault Code Guide

ABS/ATC Circuit Pin and Wire Numbers
Pin
Connector
Pin
Number
Wire
Number
Circuit Description
X3
Green
1 377LR+ Left Rear Sensor, High
2 377LR– Left Rear Sensor, Low
3 377RR+ Right Rear Sensor, High
4 377RR– Right Rear Sensor, Low
5 378T+ ATC Valve, High
6 378T– ATC Valve, Low
7 378RR0 Right Rear Modulator Valve, Out
8 378RR– Right Rear Modulator Valve, Ground
9 378RRI Right Rear Modulator Valve, In
10 378LR0 Left Rear Modulator Valve, Out
11 378LR– Left Rear Modulator Valve, Ground
12 378LRI Left Rear Modulator Valve, In
Table 1, ABS/ATC Circuit Pin and Wire Numbers
3. Connect ohmmeter probes to the sensor connec-
tor terminals and read the resistance.
• If the resistance is 900 to 2000 ohms, the
cable and the sensor circuit are good. Pro-
ceed to the "Wheel Speed Sensor Voltage"
test.
• If the resistance is less than 900 ohms or
greater than 2000 ohms, perform the next
test, "Wheel Speed Sensor Resistance."
Wheel Speed Sensor Resistance
To check the resistance in a wheel speed sensor,
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 wheel sensor cable from the
chassis harness.
3. Connect ohmmeter probes to the pins on the
sensor and read the resistance.
• If the resistance reading is 900 to 2000
ohms but the resistance noted in the previ-
ous test, "Wheel Speed Sensor and Circuit
Resistance" was not, repair or replace the
chassis harness wiring.
• If the resistance is less than 900 ohms or
greater than 2000 ohms, clean the termi-
nals and check the resistance again.
• If the resistance reading is still not correct,
replace the sensor. See Subject 110 for
instructions.
4. Install the connectors and remove the chocks
from the tires.
Wheel Speed Sensor Voltage
NOTE: PC diagnostics can be used for this test
to compare speed signal output of all sensors. A
problem will be indicated by low or erratic out-
put.
To check the voltage output of a wheel speed sen-
sor:
1. Park the vehicle on a level surface, set the park-
ing brake, and shut down the engine.
2. Chock the tires of the axle not being tested.
Raise the vehicle and put jack stands under the
axle so the wheels can rotate.
3. Disconnect the applicable connector from the
ABS ECU for the sensor being tested. See
Table 1.
Meritor WABCO Pneumatic Antilock Braking System
(ABS)
42.00
Testing
Business Class M2 Workshop Manual, Supplement 0, January 2002 170/3