MWO-9-2320-272-35-1
MODIFICATION OF 5-TON M939, M939A1, M939A2 SERIES FAMILY OF VEHICLES (FOV)
M939 BRAKE STABILIZATION PROGRAM (RETROFIT OF ANTI-LOCK BRAKE SYSTEM (ABS) FOR M939 FOV); MODIFICATION WORK ORDER
JANUARY 2007
CHANGE 1
MWO-9-2320-272-35-1 - Page 28 of 109
MWO 9-2320-272-35-1
26
(8)
Diagnostic Code Descriptions.
(a)
Code 00, 07, 8.8, and C1. Indicates that the system is working. Diagnostic tester will
indicate 00 with vehicle moving and 07 when vehicle is stationary indicating that there are
no active faults. Code 8.8 is a self diagnostic test. Code C1 indicates that the ABS is a 2S/2M
system (two sensors with modulator valves).
(b)
Code 03 or 04. Indicates that a wheel sensor or wheel sensor lead has a short or open circuit.
Disconnect wheel sensor lead from wiring harness lead and measure the resistance between
the two pins of wheel sensor lead. The ohmmeter reading should be between 980 and 2350
Ohms. Replace wheel sensor if not within limits. To check wiring harness lead, disconnect
ABS main wiring harness connector from ECU and check for short or open circuit between
sensor lead pins 1 and 10 (table 2) for 2A right rear wheel wheel sensor and pins 2 and 11
for 2B left rear wheel sensor. Also check for damaged connector pins. Replace or repair as
necessary.
NOTE
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.
(c)
Codes 13 or 14. 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 AC meter 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. 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:
— Dragging brake
— Pinched or kinked air delivery hose
— Defective modulator valve or failed primary air system
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
30-36 Ohms between bottom pins. Check for 15-18 Ohms between either bottom pin and 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 (table 2) 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 (table 2). 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 (table 2). Replace ECU or ABS
main wiring harness as necessary.
(f)
Codes 72, 73, 78, and 79. Indicate that a solenoid or its cable has a short to ground. The most
likely cause is a damaged cable or solenoid. To check this, remove ABS main wiring harness
connector from ECU and check for continuity between pins 3, 13, and 23 for (BLUE) forward
valve cable and 4, 14, and 24 for (YELLOW) rear valve cable and vehicle B+, with battery
and starter switches in the ON or RUN position. If resistance is less than 10M
Ω
in any test,
move battery and starter switches to the OFF position. Repair or replace ABS main wiring
harness connector or defective ECU.
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