Testing Procedure Dodge Ram Wagon B3500

Testing Procedure

For connector terminal identification, see CONNECTOR IDENTIFICATION. For wiring diagrams, see WIRING DIAGRAMS. (Scheme 84)for diagnostic instructions.

Scheme 84

Open RWAL dump solenoid

Dump solenoid is energized by battery voltage sent by CAB if isolation solenoid action is not enough to eliminate wheel-lock conditions. Dump solenoid allows brake fluid to flow away from brake cylinders into an accumulator. CAB will pulse dump solenoid activations and allow a maximum of 16 dump cycles in a complete anti-lock stop action. CAB deactivates dump solenoid when rear wheel deceleration rate matches programmed limit.

1. Ground connection for HCU
2. Open circuit in HCU dump solenoid
3. Poor connections in 14-pin CAB connector
4. Poor connections in 4-pin HCU connector
5. Faulty CAB unit.

For connector terminal identification, see CONNECTOR IDENTIFICATION. For wiring diagrams, see WIRING DIAGRAMS. (Scheme 85)for diagnostic instructions.

Scheme 85

Short to ground in HCU RWAL reset switch circuit.

If brake pedal is released during an anti-lock stop, the RWAL reset switch contacts open and indicate to the CAB that brake fluid pressure has equalized across the HCU. CAB then resets dump solenoid cycle counter to zero so another complete anti-lock stop action is possible. Brake fluid that was sent to accumulator is forced back into hydraulic circuit.

Short circuit in HCU RWAL reset switch or harness wiring.

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 86)for diagnostic instructions.

Scheme 86

1. Mechanical malfunction in rear brakes
2. Faulty rear wheel speed sensor or exciter ring

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 87)for diagnostic instructions.

Scheme 87

Open 4X4 switch sense circuit.

Vehicles equipped with 4-wheel drive have an indicator switch mounted to transfer case or front axle. This switch is closed to ground when the transfer case is shifted into 4WD mode. While in 4-wheel drive, switch is closed and indicates to CAB that both axles are operating together. CAB extends maximum number of dump solenoid dump cycles in the event of anti-lock braking.

1. Mechanical function in rear brakes
2. Faulty 4X4 switch and/or switch circuit
3. Bald tires
4. RWAL valve

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 88)for diagnostic instructions.

Scheme 88

Intermittent poor connection in wheel speed sensor circuits.

Vehicle speed is calculated by comparing magnetic induction (AC voltage sine wave) signal generated by wheel speed sensor/exciter ring to a time value. The CAB compares the frequency of the sine wave to a time value to calculate vehicle speed. During braking, CAB monitors rate of rear wheel deceleration and checks for wheel-lock conditions.

1. Debris built up on tip of wheel speed sensor
2. Broken, chipped or missing teeth on exciter ring
3. Bent exciter ring
4. Faulty wheel speed sensor

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 89)for diagnostic instructions.

Scheme 89

Short to ground in RWAL isolation solenoid circuit.

If the CAB senses that rear wheel speed deceleration is excessive, it will energize the isolation solenoid by providing battery voltage to the solenoid. This prevents a further increase of driver induced brake pressure to the rear wheels. The CAB unit has an internal fuse as a fail-safe for ABS control. Rear brake isolation and dump solenoids cannot be activated by CAB if fuse is open. Brake system operates normally but without ABS control over rear brakes.

1. Short to ground in RWAL isolation solenoid
2. Fuse pellet in CAB open
3. Faulty CAB unit

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 90)for diagnostic instructions

Scheme 90

Short to ground in RWAL dump solenoid circuit.

When CAB detects wheel-lock conditions, an isolation solenoid is energized to prevent further fluid pressure increase pressure to rear brakes. If this action does not eliminate wheel-lock conditions, a second dump (pressure-venting) solenoid is activated for a few milliseconds to allow existing fluid pressure to flow away from rear brakes into an accumulator. CAB monitors fluid release amount and rate and pulses the dump solenoid until ring gear deceleration rate is within programmed limit. CAB deactivates solenoids when wheel-lock conditions no longer exist.

1. Short circuit in HCU dump solenoid
2. Short to ground in RWAL dump solenoid
3. Faulty CAB unit

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 91)for diagnostic instructions.

Scheme 91

Open circuit in wheel speed sensor circuits between 14-pin CAB connector and rear wheel speed sensor.

Vehicle speed is calculated by comparing magnetic induction signal (AC voltage sine wave) generated by wheel speed sensor/exciter ring to a time value. The CAB compares the frequency of the sine wave to a time value to calculate wheel speed. During braking, CAB monitors rate of rear wheel deceleration and checks for wheel-lock conditions.

1. Poor connection in 14-pin CAB connector
2. Poor connection in rear wheel speed sensor connector
3. Faulty rear wheel speed sensor

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 92)for diagnostic instructions.

Scheme 92

Short circuit in rear wheel speed sensor circuits.

Vehicle speed is calculated by comparing magnetic induction signal (AC voltage sine wave) generated by wheel speed sensor/exciter ring to a time value. The CAB compares the frequency of the sine wave to a time value to calculate wheel speed. During braking, CAB monitors rate of rear wheel deceleration and checks for wheel-lock conditions.

1. Short circuit in wheel speed sensor circuits
2. Faulty rear wheel speed sensor

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 93)for diagnostic instructions.

Scheme 93

CAB senses brakes being continuously activated while vehicle exceeds 40 MPH.

The primary function of the switch is to turn on brake lights when braking. The switch sends signals to vehicle systems that must know when vehicle is braking. When the switch contacts open (brakes applied), the CAB receives the brake applied signal. The Powertrain Control Module receives a signal from the brake lamp switch to cancel cruise control when brakes are applied. The CAB receives signal from brake lamp switch to begin monitoring differential ring gear deceleration rate and ABS.

1. Open circuit between terminal 7 and stop lamp switch in 14-pin CAB connector
2. Poor connection in 14-pin CAB connector
3. Poor connection in brake lamp switch connector
4. Open circuit from brake lamp switch to ground
5. Misadjusted brake lamp switch
6. Faulty brake lamp switch
7. Faulty CAB unit

For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS .

(Scheme 94)for diagnostic instructions.

Scheme 94

CAB must experience a lock loop failure

The CAB primary functions are

1. Detecting wheel-lock tendencies
2. Controlling brake fluid pressure to rear brakes during anti-lock braking
3. Monitoring the RWAL system for proper operation
4. Running self-checking diagnostics

The CAB generates and stores DTC's for detected faults. One fault at a time can be stored in memory. Detected faults trigger a red brake warning light and an amber ABS warning light located on instrument panel. DTC's remain in memory when ignition is shut off with the exception of DTC's 9 and 11. These two codes are erased when ignition is turned off and then are stored in memory the next time the ignition is turned on, provided system fault still exists.

Fault in CAB unit

The CAB is the only component of the RWAL system that can set DTC 12A. Code only occurs when phase lock loop failure occurs.

The CAB must experience a program check failure

The CAB primary functions are

1. Detecting wheel-lock tendencies
2. Controlling brake fluid pressure to rear brakes during anti-lock braking
3. Monitoring the RWAL system for proper operation
4. Running self-checking diagnostics

The CAB generates and stores DTC's for detected faults. One fault at a time can be stored in memory. Detected faults trigger a red brake warning light and an amber ABS warning light located on instrument panel. DTC's remain in memory when ignition is shut off with exception of DTC's 9 and 11. These two codes are erased when ignition is turned off and then are stored in memory the next time the ignition is turned on, provided system fault still exists.

Fault in CAB unit

CAB is the only component of the RWAL system that can set DTC 12B. Code only occurs when program check failure occurs.

CAB must experience a RAM failure

The CAB primary functions are

1. Detecting wheel-lock tendencies
2. Controlling brake fluid pressure to rear brakes during anti-lock braking
3. Monitoring the RWAL system for proper operation
4. Running self-checking diagnostics

The CAB generates and stores DTC's for detected faults. One fault at a time can be stored in memory. Detected faults trigger a red brake warning light and an amber ABS warning light located on instrument panel. DTC's remain in memory when ignition is shut off with exception of DTC's 9 and 11. These two codes are erased when ignition is turned off and then are stored in memory the next time the ignition is turned on, provided system fault still exists.

Fault in CAB unit

The CAB is the only component of the RWAL system that can set DTC 12C. Code only occurs when RAM failure occurs.