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

Anti-Lock Control - Non-Hybrid

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

Normal Operation

The operating voltage required to supply the ABS module, hydraulic pump and isolation valves is in a range between 10 and 16 volts. The ABS module uses input from several different sensors (wheel speed sensors, Brake Pedal Position (BPP) switch, sensor cluster, etc.) to determine if an ABS event is necessary. If an ABS event is necessary, the ABS module commands the hydraulic pump motor on and command the Hydraulic Control Unit (HCU) to actuate the appropriate solenoids. During an ABS event, the front and rear end of the vehicle should track true to the direction of travel along the vehicle centerline unless driver input dictates otherwise, there is an internal issue with the HCU (Hydraulic Control Unit) or an issue with the base brake system (caliper, tubes, etc.) that allows one or more wheels to lock up.

Fused battery voltage is supplied to the ABS module from Battery Junction Box (BJB) fuse 10 (30A) along circuit SBB10 (YE/RD) and fuse 8 (40A) along circuit SBB08 (VT/RD). Fused ignition voltage is supplied to the ABS module from Smart Junction Box (SJB) fuse 42 (10A) along CBP42 (GN) and ground is provided to the module along circuit GD123 (BK/GY).

This pinpoint test is intended to diagnose the following:

- Base brake system

- HCU (Hydraulic Control Unit)

PINPOINT TEST L : POOR VEHICLE TRACKING DURING ANTI-LOCK FUNCTION

L1 BLEED THE BRAKE SYSTEM

- Bleed the brake system using the scan tool.

- 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 sticking valve in the HCU (Hydraulic Control Unit).

No
GO to L2.

L2 VERIFY VEHICLE TRACKING DURING NON-ABS BRAKING

- Test drive the vehicle and verify vehicle tracking during normal braking.

Does the vehicle track correctly during normal braking?

Yes
GO to L3.

No
The condition could be caused by a base brake component or vehicle alignment. REFER to Brakes and Traction Control to verify base brake components and REFER to Suspension &/or Alignment to verify suspension components.

L3 CHECK THE ABS INLET VALVE (CLOSED POSITION)

- With the vehicle in NEUTRAL, position it on a hoist.

- Rotate all the wheels to make sure they rotate freely (the transaxle must be in NEUTRAL).

- Connect the scan tool.

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: ABS DataLogger.

- Apply moderate brake pedal effort.

- Toggle the left front inlet valve (LF_INLET) active command ON and at the same time, have an assistant attempt to rotate the LF wheel.

Does the LF wheel rotate?

Yes
TOGGLE the LF_INLET output command OFF. GO to L4.

No
TOGGLE the LF_INLET output command OFF. INSTALL a new HCU (Hydraulic Control Unit). REFER to Hydraulic Control Unit (HCU) . TEST the system for normal operation.

L4 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 (Hydraulic Control Unit). REFER to Hydraulic Control Unit (HCU) . TEST the system for normal operation.

No
GO to L5.

L5 CHECK THE ABS OUTPUT VALVE (OPEN POSITION)

- Apply moderate brake pedal effort.

- NOTE: Each activation of the output command runs the pump for 2 seconds.
Toggle the following active commands ON:
- LF_INLET

- Left front outlet valve (LF_OUTLET)

- Hydraulic pump motor (PMP_MOTOR)
- At the same time, have an assistant attempt to rotate the LF wheel.



Does the LF wheel rotate?

Yes
TOGGLE all output commands OFF. GO to L6.

No
TOGGLE all output commands OFF. INSTALL a new HCU (Hydraulic Control Unit). REFER to Hydraulic Control Unit (HCU) . TEST the system for normal operation.

L6 CHECK THE ABS INLET AND OUTLET VALVE (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 (Hydraulic Control Unit). REFER to Hydraulic Control Unit (HCU) . TEST the system for normal operation.

No
Beginning with Step L3, REPEAT this procedure for the RF, LR and RR wheels using the appropriate output commands. If no failure occurs, the system is operating normally.