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Test H: Poor Vehicle Tracking During Anti-Lock Function, Light Off

Verify Complaint

Verify condition exists. Bleed brake system. See BLEEDING BRAKE SYSTEM . If vehicle still does not track properly, go to next. If vehicle tracks properly after bleeding brakes, problem is corrected.

Check ABS Pump Motor Operation

Connect scan tester to Data Link Connector (DLC). Using scan tester, put ECU into active command mode. Command pump motor relay to run. If pump motor runs, command pump motor relay to off and go to next step. If pump motor does not run, go to DTC C1095 .

Check Left Front ABS Valve Function

Raise and support vehicle. Turn ignition on. While rotating left front wheel, moderately apply brake pedal. If wheel rotates, replace HCU. If wheel does not rotate, go to next step.
NOTE: Left front ABS inlet valve must be activated before applying brake pressure. After completing next test step, return left front ABS inlet valve to off position.

Check Left Front ABS Inlet Valve Function

With scan tool in active command mode, command left front ABS inlet valve to On. While rotating left front wheel, moderately apply brake pedal. If left front wheel does not rotate, replace HCU. If left front wheel rotates, go to next step.

Check Left Front ABS Outlet Valve Function

With scan tester, command left front inlet valve, outlet valve and pump motor relay on while still applying brake pedal. If brake pedal rises, go to next step. If brake pedal does not rise, replace HCU. Command all left front ABS valves and pump motor relay off.

Check Right Front ABS Valve Function

Turn ignition on. While rotating right front wheel, moderately apply brake pedal. If wheel rotates, replace HCU. If wheel does not rotate, go to next step.

Check Right Front ABS Inlet Valve Function

Be sure inlet valve in actuated. With scan tester in active command mode, command right front inlet valve to on. While rotating right front wheel, moderately apply brake pedal. If right front wheel does not rotate, replace HCU. If right front wheel rotates, go to next step. Return ABS inlet valve to off.

Check Right Front ABS Outlet Valve

Command right front inlet valve, outlet valve and pump motor relay to on while still applying light brake pedal. If brake pedal rises, go to next step. If brake pedal does not rise, replace HCU. Return pump motor relay, outlet and inlet valves to off.

Check Left Rear ABS Valve Function

Raise and support vehicle. Turn ignition on. While rotating left rear wheel, moderately apply brake pedal. If wheel rotates, replace HCU. If wheel does not rotate, go to next step.

Check Left Rear ABS Inlet Valve Function

Be sure left rear ABS inlet valve is open before applying brake pedal. With scan tester in active command mode, command left rear ABS inlet valve on. While rotating left rear wheel, moderately apply brake pedal. If left rear wheel does not rotate, replace HCU. If left rear wheel rotates, go to next step. Return left rear ABS inlet valve to off.

Check Left Rear ABS Outlet Valve

Command left rear inlet valve, outlet valve and pump motor relay on while still applying brake pedal. If brake pedal rises, go to next step. If brake pedal does not rise, replace HCU. Command inlet valve, outlet valve and pump motor relay off.

Check Right Rear ABS Valve Function

Raise and support vehicle. Turn ignition on. Apply moderate brake pressure while turning right rear wheel. If wheel turns, replace HCU. If wheel does not turn, go to next step.

Check Right Rear ABS Inlet Valve Function

With scan tester in active command mode, command right rear inlet valve on. While rotating right rear wheel, moderately apply brake pedal. If wheel rotates, go to next step. If wheel does not rotate, replace HCU. Restore inlet valve to off position.

Check Right Rear ABS Outlet Valve Function

Command right rear ABS inlet valve, outlet valve and ABS pump motor relay on. While rotating right rear wheel, moderately apply brake pedal. If brake pedal rises, See appropriate DISC & DRUM article. If brake pedal does not rise, replace HCU. Command inlet and outlet valves and pump motor relay to off. Restore all connections. Retest system.