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

F1 CHECK THE BASE BRAKE SYSTEM 

• Inspect the base brake system.
• Is the base brake system OK? 

Yes 

GO to F2.

No 

REFER to BRAKE SYSTEM-GENERAL INFORMATION .

F2 BLEED THE BRAKE SYSTEM 

• Bleed the brake system. Refer to BRAKE SYSTEM-GENERAL INFORMATION .
• Place the air suspension switch in the ON position after the vehicle is off the hoist.
• Does the vehicle track poorly? 

Yes 

GO to F3.

No 

The brake system is operating correctly. TEST the system for normal operation.

F3 CHECK THE LF HYDRAULIC CONTROL UNIT (HCU) VALVE OPERATION 

• Place the air suspension switch in the OFF position.
• Key in ON position.
• Connect the diagnostic tool.
• Lift the vehicle and rotate all the wheels to make sure they turn freely (the transmission must be in NEUTRAL).
• Trigger the ABS module active command PMP MOTOR ON for four seconds. (Trigger must be pushed twice. Each press runs the pump for two seconds.)
• 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 F4.

F4 CHECK THE LF HCU VALVE RELEASE 

• Trigger the ABS module active command LF INLET ON and LF OUTLET ON.
• Have an assistant turn the LF wheel using a two foot lever, such as a breaker bar, immediately after pressing trigger (the diagnostic tool will energize the valves for only two seconds per trigger press).
• Does the LF wheel turn? 

Yes 

GO to F5.

No 

GO to F6.

F5 CHECK THE RF HCU VALVE OPERATION 

• Key in ON position.
• Trigger the ABS module active command PMP MOTOR ON for four seconds. (Trigger must be pushed twice. Each press runs the pump for two seconds.) Apply moderate brake pedal effort.
• Have an assistant attempt to rotate the RF wheel.
• Does the RF wheel rotate? 

Yes 

INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT - (HCU) . TEST the system for normal operation.

No 

GO to F6.

F6 CHECK THE RF HCU VALVE RELEASE 

• Trigger the ABS module active command RF INLET ON and RF OUTLET ON.
• Have an assistant turn the RF wheel using a two foot lever, such as a breaker bar, immediately after pressing trigger (the diagnostic tool will energize the valves for only two seconds per trigger press).
• Does the RF wheel turn? 

Yes 

GO to F7.

No 

GO to F11.

F7 CHECK THE LR HCU VALVE OPERATION 

• Key in ON position.
• Trigger the ABS module active command PMP MOTOR ON for four seconds. (Trigger must be pushed twice. Each press runs the pump for two seconds.) l Apply moderate brake pedal effort.
• Have an assistant attempt to rotate the LR wheel.
• Does the LR wheel rotate? 

Yes 

INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT - (HCU) . TEST the system for normal operation.

No 

GO to F8.

F8 CHECK THE LR HCU VALVE RELEASE 

• Trigger the ABS module active command LR INLET ON and LR OUTLET ON.
• Have an assistant turn the LR wheel using a two foot lever, such as a breaker bar, immediately after pressing trigger (the diagnostic tool will energize the valves for only two seconds per trigger press).
• Does the LR wheel turn? 

Yes 

GO to F9.

No 

GO to F11.

F9 CHECK THE RR HCU VALVE OPERATION 

• Key in ON position.
• Trigger the ABS module active command PMP MOTOR ON for four seconds. (Trigger must be pushed twice. Each press runs the pump for two seconds.)
• Apply moderate brake pedal effort.
• Have an assistant attempt to rotate the RR wheel.
• Does the RR wheel rotate? 

Yes 

INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT - (HCU) . TEST the system for normal operation.

No 

GO to F10.

F10 CHECK THE RR HCU VALVE RELEASE 

• Trigger the ABS module active command RR INLET ON and RR OUTLET ON.
• Have an assistant turn the RR wheel using a two foot lever, such as a breaker bar, immediately after pressing trigger (the diagnostic tool will energize the valves for only two seconds per trigger press).
• Does the RR wheel turn? 

Yes 

The ABS is operating correctly. TEST the system for normal operation.

No 

GO to F11.

F11 CHECK FOR DIAGNOSTIC TROUBLE CODES (DTCS) 

• Retrieve and document continuous DTCs.
• Are any DTCs retrieved? 

Yes 

GO to the ANTI-LOCK BRAKE SYSTEM (ABS) MODULE DIAGNOSTIC TROUBLE CODE (DTC) INDEX .

No 

INSTALL a new HCU. REFER to HYDRAULIC CONTROL UNIT - (HCU) . TEST the system for normal operation.