TM-9-2320-272-23-2
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 2 OF 5
SEPTEMBER 2012
TM-9-2320-272-23-2 - Page 57 of 1417
INTRODUCTION - Continued
c.
Codes 13 or 14.
NOTE
If the gap on both sensors is too great, you may not show a fault. The ECU will
think the vehicle is not moving and you will not have ABS brakes.
Occurs when vehicle is moving and indicates that the wheel sensor output is insufficient for a moving
vehicle. The most likely reason for this code is that the gap between wheel sensor and tone ring is
too great. Lift and support rear-rear axle wheels, disconnect wheel sensor leads and connect a
multimeter to right or left wheel sensor leads. Measure AC voltage while rotating wheel at a rate of
one revolution every two seconds. The output voltage should be at least 200 millivolts (.002 VAC).
If less than limit, try pushing wheel sensor in until sensor connects tone ring and recheck voltage.
If voltage is not within limit, replace wheel sensor.
d.
Codes 23 or 24. Occurs when vehicle is moving and indicates that there is an intermittent loss of
sensor signal. This type of fault is often difficult to diagnose. The most likely causes include:
a.
Dragging brake
b.
Pinched or kinked air delivery hose. Defective modulator valve or failed primary air system.
c.
Check brakes to ensure that they release completely and look for visual external damage
to delivery hoses or delivery tubes. Check exhaust ports of ABS valves for obstruction.
Repair or replace defective hardware as necessary.
e.
Code 62, 63, 68, or 69 indicates that a solenoid or its cable has an open circuit internally. The most
likely causes include bad solenoid or loose solenoid connection. Disconnect the appropriate
solenoid connector and check resistance at the solenoid pins. Check for 30 to 60 Ohms between
either bottom pin or the top pin. Check the female terminals on the connector for excessive pin
spread or corrosion. Replace defective solenoid or connector as required. Additional possible
causes are a bad solenoid cable, ABS main wiring harness connector not completely latched into
the ECU, or a damaged harness pin. Attach the solenoid cable (figure 1) to solenoid. Remove main
wiring harness connector from ECU and check the resistance between pins 3 and 13, 3 and 23, and
13 and 23 for forward (BLUE) valve cable or between 4 and 14, 4 and 24, and 14 and 24 for rear
(YELLOW) valve cable (figure 1). The resistance should be approximately 32 Ohms between pins
3 and 13 and 4 and 14 and resistance should be approximately 16 Ohms between pins 3 and 23,
13 and 23, 4 and 24, and 14 and 24 (figure 1). Replace ECU or ABS main wiring harness as
necessary.
TM 9-2320-272-23-2
0154
0154-2
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