Pinpoint Test H: Poor Vehicle Tracking During Anti-Lock Function

H1 BLEED THE BRAKE SYSTEM
- Bleed the brake system using the diagnostic tool. Refer to BRAKE SYSTEM BLEEDING .
- Test drive the vehicle.
- Does the vehicle track correctly?
- Yes : The brake system is operating correctly. The concern may have been caused by air in the hydraulic system or a sticky valve.
- No : GO to H2.
H2 CHECK THE ABS INLET VALVE (CLOSED POSITION)
- Key in ON position.
- Enter the following diagnostic mode on the diagnostic tool: ABS Module Active Command.
- With the vehicle in NEUTRAL, position it on a hoist. Refer to JACKING & LIFTING .
- Rotate all the wheels to make sure they rotate freely (the transmission must be in NEUTRAL).
- Trigger the ABS module LF INLET ON active command.
- Apply moderate brake pedal effort.
- Have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
- Yes : TRIGGER the LF INLET OFF active command. GO to H3.
- No : INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT (HCU) . TEST the system for normal operation.
H3 CHECK THE ABS INLET VALVE (OPEN POSITION)
- Apply moderate brake pedal effort.
- Have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
- Yes : INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT (HCU) . TEST the system for normal operation.
- No : GO to H3.
H4 CHECK THE ABS OUTPUT VALVE (OPEN POSITION)
- Apply moderate brake pedal effort.
- Trigger ABS module LF INLET ON active command.
- Trigger ABS module ABS POWER ON active command (turns on the pump motor) for 6 seconds. (The trigger must be pressed 3 times. Each press runs the pump for 2 seconds.)
- Trigger the ABS module LF OUTLET ON active command, then trigger the ABS module LF OUTLET OFF active command. Repeat 3 times.
- Have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
- Yes : TRIGGER all active commands OFF. GO to H5.
- No : INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT (HCU) . TEST the system for normal operation.
H5 CHECK THE ABS INLET & OUTLET VALVES (CLOSED POSITION)
- Apply moderate brake pedal effort.
- Have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
- Yes : INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT (HCU) . TEST the system for normal operation.
- No : REPEAT this procedure (beginning with Step H2) for the RF, LR and RR wheels using the appropriate active commands. If no failure occurs, the system is operating normally.