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4WABS Components
Light Flash Technique
1. Note: If 12V test light is not available, the amber ABS warning light also flashes during this test. Locate test connector in the engine compartment and install 12V test light between Pins C and E.
2. With the ignition off, jumper Pin E to B.
3. Turn key to RUN position.
4. Remove jumper between Pins E and B after 5 seconds.
5. Count light flashes of test light or amber ABS warning light.
Manually Clearing Diagnostic Codes: All diagnostic trouble codes must be output, all concerns corrected (anti-lock light off) and vehicle driven about 40 km/h (25 mph) before diagnostic trouble codes will be erased.
Note: Do not raise vehicle on hoist and accelerate to 40 km/h (25 mph) to simulate driving the vehicle. Erroneous sensor codes will be set.
Automatic Memory Erasing: A diagnostic trouble code will be automatically erased if no system concerns occur for 50 ignition cycles.
The front inlet valves should read 5-8 Ohms each; all other valves should read 3-6 Ohms each. Sensors should read 800-1400 Ohms across the pins, and more than 10 Ohms from the metal shell to either pin. The pump motor sensor should be 5-40 Ohms. The acceleration sensor is a group of switches which should be closed when the truck is stationary & level. When the sensor is tilted ~1" up in the rear, pins 2-3 should go open; when tilted ~1.5" up in the front, pins 1-3 should go open.
Codes:
11 Possible Source(s):
· Anti-lock brake electronic control module failure.
Action(s) to take:
· REPLACE anti-lock brake electronic control module.
16 Possible Source(s):
· System OK.
Action(s) to take:
· None.
17 Reference Voltage/Intermittent Valve Fault
Possible Source(s):
· 30 amp fuse open.
· Intermittent connections to battery, main relay or ground.
· Main relay coil or contacts open.
· Open or short to ground in Circuit 532 (O/Y).
· Open or short to ground in Circuit 599 (PK/LG).
· Open or short to ground in Circuit 601 (LG/PK).
· Short to ground through anti-lock hydraulic control unit.
· Intermittent valve failures.
· High resistance valves.
22 Front Left Inlet Solenoid Valve Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 495 (T).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 40.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 6.
· Open or shorted inlet front left valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
23 Front Left Outlet Solenoid Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 496 (O).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 26.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 7.
· Open or shorted outlet front left valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
24 Front Right Inlet Solenoid Valve Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 497 (W).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 34.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 8.
· Open or shorted inlet front right valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
25 Front Right Outlet Solenoid Valve Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 498 (PK).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 15.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 5.
· Open or shorted outlet front right valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
26 Rear Axle Inlet Solenoid Valve Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 499 (GY/BK).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 33.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 2.
· Open or shorted inlet rear axle valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
27 Rear Axle Outlet Solenoid Concern Diagnosis
Possible Source(s):
· Intermittent open Circuit 510 (T/R).
· Terminal backout in anti-lock brake electronic control module connector Pins 17 and 27.
· Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 3.
· Open or shorted outlet rear axle valve coil.
· Open or shorted driver in anti-lock brake electronic control module.
31 Left Front Brake Anti-Lock Sensor Diagnosis (Static)
Possible Source(s):
· Poor connection at left front brake anti-lock sensor.
· Terminal damage or backout in anti-lock brake electronic control module connector Pins 24 and 25.
· Terminal damage or backout in two-pin sensor connector.
· Open or shorted left front brake anti-lock sensor.
· Open or shorted Circuit 521 (T/O) or 522 (T/BK).
· Improper front left anti-lock brake sensor cable routing leading to above.
· Defective front left wheel speed sensor electrical test circuit in anti-lock brake electronic control module.
32 Right Front Brake Anti-Lock Sensor Diagnosis
Possible Source(s):
· Poor connection at right front brake anti-lock sensor.
· Terminal damage or backout in anti-lock brake electronic control module connector Pins 36 or 23.
· Terminal damage or backout in two-pin anti-lock brake sensor connector.
· Open or shorted right front brake anti-lock sensor.
· Open or shorted Circuit 514 (Y/R) or 516 (Y/BK).
33 Rear Axle Speed Sensor Diagnosis
Possible Source(s):
· Poor connection at vehicle speed sensor.
· Terminal damage or backout in anti-lock brake electronic control module connector Pins 21 or 22.
· Terminal damage or backout in two-pin sensor connector.
· Open or shorted vehicle speed sensor coil.
· Open or shorted Circuit 518 (LG/R) or 519 (LG/BK).
· Improper vehicle speed sensor cable routing leading to above.
· Defective vehicle speed sensor electrical test circuit in anti-lock brake electronic control module. Note: some vehicles were built using Circuit 523 (R/PK) in place of 518 (LG/R).
35
41
55
75 Left Front Brake Anti-Lock Sensor Diagnosis (Dynamic)
Possible Source(s):
· Damaged/missing front brake anti-lock sensor indicator teeth or missing front brake anti-lock sensor indicator.
· Air gap too small or too large.
· Excessive axle vibration.
· Weak front brake anti-lock sensor.
· Loose front brake anti-lock sensor.
· INTERMITTENT short or open in Circuit 521 (T/O) or 522 (T/BK).
· Disturbances caused by ignition or radio frequency interference.
· Defective trigger circuit in anti-lock brake electronic control module.
36
42
56
76 Right Front Brake Anti-Lock Sensor Diagnosis (Dynamic)
Possible Source(s):
· Damaged/missing front brake anti-lock sensor indicator teeth or missing front brake anti-lock sensor indicator.
· Air gap too small or too large.
· Excessive axle vibration.
· Weak front brake anti-lock sensor.
· Loose front brake anti-lock sensor.
· INTERMITTENT short or open in Circuit 514 (Y/R) or 516 (Y/BK).
· Disturbances caused by ignition or radio frequency interference.
· Defective trigger circuit in anti-lock brake electronic control module.
37
43
57
77 Rear Axle Speed Sensor Diagnosis (Dynamic)
Possible Source(s):
· Damaged/missing indicator ring teeth or missing indicator ring.
· Air gap too small or too large.
· Excessive axle vibration.
· Weak rear axle sensor.
· Loose rear axle sensor.
· Disturbances caused by ignition or radio frequency interference.
· Defective trigger circuit in anti-lock brake electronic control module.
· Intermittent short or open in Circuit 518 (LG/R) or 519 (LG/BK). Note: Some vehicles were built using Circuit 523 (R/PK) in place of 518 (LG/R).
51 Hydraulically Inoperative Front Left Outlet Valve or Sensor Disturbance Detected
Possible Source(s):
· Pinched or closed brake line or hose.
· Worn or clogged front left outlet valve.
52 Hydraulically Inoperative Right Front Outlet Valve or Sensor Disturbance Detected
Possible Source(s):
· Pinched or closed brake line or hose.
· Worn or clogged front right outlet valve.
53 Hydraulically Inoperative Rear Axle Outlet Valve or Sensor Disturbance Detected
Possible Source(s):
· Pinched or closed brake line or hose.
· Worn or clogged rear axle outlet valve.
63 Pump Motor Triggered but Did Not Run
Possible Source(s):
· Damaged pump motor.
· Terminal backout in anti-lock brake electronic control module harness connector Pins 17, 29, 37 and 38.
· Open or shorted pump motor relay coil.
· Open contacts in pump motor relay.
· Terminal backout in pump motor 4-way, Pins 1, 2, 3 or 4.
65 Acceleration Sensor
Possible Source(s):
· Terminal backout in anti-lock brake electronic control module wiring harness connector Pins 30, 31 and 32.
· Worn or damaged acceleration switch.
· Worn or damaged anti-lock brake electronic control module.
· Acceleration switch terminal backout, Pins 1, 2 and 3.
· Short to ground in Circuits 836 (O/W), 886 (O/BK) and 887 (Y).
67 Pump Motor Running but Not Triggered
Possible Source(s):
· Damaged trigger circuit in anti-lock brake electronic control module.
· Terminal backout in anti-lock brake electronic control module harness connector Pins 2 and 3.
· Welded relay contacts.
· Short to ground in Circuit 539 (PK/LB).
-- Amber ABS Warning Lamp On, No Code
Possible Source(s):
· Worn or damaged ignition switch.
· Open ignition feed circuit to anti-lock brake electronic control module.
· Low battery voltage (less than 8V).
· Blown ignition fuse.
· Open system ground.
ABS and Speedometer Are Not Functioning Properly
Possible Source(s):
· No signal to anti-lock brake electronic control module from vehicle speed sensor.
· No signal to speedometer from anti-lock brake electronic control module.
· Defective vehicle speed sensor.
Unwarranted ABS Activity
Possible Source(s):
· Tone ring is damaged.
Action(s) to take:
· INSPECT both front brake anti-lock sensor indicators and the rear axle tone ring.
Possible Source(s):
· Sensor output is weak.
Action(s) to take:
· Left front brake anti-lock sensor -- GO to «Pinpoint Test L».
· Right front brake anti-lock sensor -- GO to «Pinpoint Test M».
· Rear axle sensor -- GO to «Pinpoint Test N».
Possible Source(s):
· Intermittent open or shorted sensor circuit.
· Intermittent open sensor circuit at intermediate connections especially bulkhead.
Possible Source(s):
· Chafed wire insulation or pinched wire due to improper routing causing intermittent short.
Action(s) to take:
· INSPECT wiring harness from front brake anti-lock sensors on knuckle to the frame and from the rear axle to the frame for worn or chafed wire insulation.
Possible Source(s):
· Rear brake adjustment too tight.
· Linings are "grabby".
Wheels Lock Up
Possible Source(s):
· Hydraulic outlet (dump) valve.
· Damp or contaminated rear brake shoe linings, stuck/leaking wheel cylinder, overadjusted rear brakes.
· Hung-up parking brake.
· Leaking rear axle seal.
Hard or Soft Brake Pedal
Possible Source(s):
· Stuck shut inlet (isolation) valve (hard) or leaky outlet (dump) valve (soft).
· Leaky inlet (isolation) valve during ABS (soft).
· Hydraulic leak in brake line or hose, fitting, brake master cylinder, wheel cylinder, or caliper.
· Air in brake system.
· Little or no vacuum boost.
· Stuck or inoperative wheel cylinder or caliper.
· Pinched or crimped brake line or hose.
Lack of Deceleration During Medium/Hard Brake Application
Possible Source(s):
· Stuck shut inlet (isolation) valve or leaky outlet (dump) valve -- rear axle ONLY.
Possible Source(s):
· Hydraulic leak in brake line or hose, fitting, brake master cylinder, wheel cylinder, or caliper.
· Air in brake system.
· Little or no vacuum boost.
· Stuck or inoperative wheel cylinder or caliper.
· Pinched or crimped brake line or hose.
· Ineffective brake shoe or pad linings.
Vehicle Pulls During Braking
Possible Source(s):
· Fully or partially blocked right front inlet (isolation) valve.
· Fully or partially blocked left front inlet (isolation) valve.
· Improperly adjusted rear brake.
· Frozen or binding caliper (one side of vehicle).
· Uneven brake pad or shoe wear.
· Pinched or crimped brake line or hose.
ABS Warning Light On Intermittently with Code 16
Possible Source(s):
· Ignition circuit 601 loose.
· INSPECT Circuit 601 harness from ignition switch to anti-lock brake electronic control module harness connector for opens/shorts especially at the bulk-head connector. CORRECT as necessary.
Possible Source(s):
· Loose anti-lock brake electronic control module grounds.
Action(s) to take:
· INSPECT anti-lock brake electronic control module grounds for looseness, corrosion or excessive dirt. CORRECT as necessary.
Possible Source(s):
· Loose power log at power distribution box.
Action(s) to take:
· CORRECT and REPAIR as necessary.
Possible Source(s):
· Low battery/charging system.
Action(s) to take:
· VERIFY ABS warning light does not come on at idle with high electrical loads.
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