Pinpoint Test G: Poor Vehicle Tracking During Anti-Lock Function
Anti-Lock Control
Pinpoint Tests
Pinpoint Test G: Poor Vehicle Tracking During Anti-lock Function
Normal Operation
The operating voltage required to operate the ABS module, hydraulic pump and isolation valves is in a range between 10 and 16 volts.
Fused ignition voltage is supplied to the ABS module from Smart Junction Box (SJB) fuse 18 (10A) along circuit 1844 (LG/RD). Fused battery voltage is supplied to the ABS module from Bussed Electrical Center (BEC) fuse 65 (30A) along circuit 601 (LB/BK) and BEC fuse 8 (40A) along circuit 534 (YE/LG). Ground is provided to the ABS module along circuit 1205 (BK). There are 2 ground circuits (one for the ABS module and one for the hydraulic pump motor) both share the same circuit number and wire color.
This pinpoint test is intended to diagnose the following:
- Base brake system
- Hydraulic Control Unit (HCU)
PINPOINT TEST G: POOR VEHICLE TRACKING DURING ANTI-LOCK FUNCTION
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G1 CHECK THE BASE BRAKE COMPONENTS
- Eliminate the base brake system as the cause of the concern.
- Is the base brake system operating correctly?
Yes
GO to G2.
No
REPAIR the base brake system. TEST the system for normal operation.
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G2 BLEED THE ABS HCU
- Bleed the HCU.
- 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 G3.
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G3 CHECK THE ABS INLET VALVE (CLOSED POSITION)
- Ignition ON.
- With the vehicle in NEUTRAL, position it on a hoist. Refer to Maintenance/Service and Repair.
- Check all the wheels to make sure they spin freely (the transmission must be in NEUTRAL).
- Enter the following diagnostic mode on the scan tool: ABS DataLogger: Left Front Inlet Valve (ABSLF_I) Output Command.
- Toggle the ABSLF_I output command ON.
- Apply moderate brake pedal effort.
- Have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
Yes
TOGGLE the ABSLF_I output command OFF. GO to G4.
No
TOGGLE the ABSLF_I output command OFF. INSTALL a new HCU. REFER to Hydraulic Control Unit (HCU) Removal and Replacement. TEST the system for normal operation.
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G4 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) Removal and Replacement. TEST the system for normal operation.
No
GO to G5.
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G5 CHECK THE ABS OUTPUT VALVE (OPEN POSITION)
- Apply moderate brake pedal effort.
- Enter the following diagnostic mode on the scan tool: ABS DataLogger.
- Left Front Inlet Valve (ABSLF_I) Output Command
- Pump Motor (ABS_MTR) Output Command
- Left Front Outlet Valve (ABSLF_O) Output Command
- Toggle the ABSLF_I output command ON.
- Toggle the ABS_MTR output command ON for 6 seconds. (The output command must be toggled ON 3 times. Each toggle runs the pump for 2 seconds.)
- Toggle the ABSLF_O output command ON.
- Toggle the ABSLF_O output command OFF. Repeat 3 times.
- While the output commands are toggled ON, have an assistant attempt to rotate the LF wheel.
- Does the LF wheel rotate?
Yes
TOGGLE all output commands OFF. GO to G6.
No
TOGGLE all output commands OFF. INSTALL a new HCU. REFER to Hydraulic Control Unit (HCU) Removal and Replacement. TEST the system for normal operation.
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G6 CHECK THE ABS INLET AND 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) Removal and Replacement. TEST the system for normal operation.
No
REPEAT this procedure (beginning with Step G2) for the RF, LR and RR wheels using the appropriate output commands. If no failure occurs, the system is operating normally.
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