Inspection Procedure 16: HSA (Hill Start Assist) Works on A Flat Road

Inspection Procedure 16: HSA (Hill Start Assist) works on a flat road.

CAUTION
^ If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines (Refer to CAN Bus Diagnostics Table CAN Bus Diagnostics Table).
^ Whenever ECU is replaced, ensure that the CAN bus lines are normal.
^ When the hydraulic unit (integrated with ASC-ECU) is replaced, always carry out the calibration of the steering wheel sensor, the G and yaw rate sensor and brake fluid pressure sensor.

COMMENTS ON TROUBLE SYMPTOM
^ A failure may have occurred in the calibration or the G and yaw rate sensor.
^ Some drivers mistake a brake dragging for HSA operation.
^ If the suspension is modified, the vehicle posture changes, and the ASC-ECU judges that the vehicle is on a steep slope and may activate HSA.

PROBABLE CAUSES
^ Improper installation of the G and yaw rate sensor
^ G and yaw rate sensor malfunction
^ ASC-ECU malfunction
^ Brake drag
^ Damaged wiring harness and connectors

DIAGNOSIS

Required Special Tools:
^ MB991958: Scan Tool (M.U.T.-III Sub Assembly)
^ MB991824: Vehicle Communication Interface (V.C.I.)
^ MB991827: M.U.T.-III USB Cable
^ MB991910: M.U.T.-III Main Harness A

STEP 1. HSA operation check
Check if the HSA works on a flat road with one occupant (driver) only in the vehicle.
Q: Does the HSA work on a flat road?
YES: Go to Step 2
NO: This diagnosis is complete.

STEP 2. Using scan tool MB991958, check the data list
Check the following service data (Refer to Scan Tool Testing and Procedures).
^ Item 09: G sensor
Q: Is the check result normal?
YES: Go to Step 5.
NO: Go to Step 3

STEP 3. G and yaw rate sensor installation check
Check that the G and yaw rate sensor is installed correctly.
Q: Is the check result normal?
YES: Carry out the calibration of the G and yaw rate sensor. Then go to Step 4
NO: Reinstall the G and yaw rate sensor correctly and then go to Step 6.

STEP 4. Brake drag check
Check the brake system for drag.
Q: Is the check result normal?
YES: Go to Step 5
NO: Repair the brake drag, and then go to Step 5.

STEP 5. Retest the system.
Check if the HSA works on a flat road with one occupant (driver) only in the vehicle.
Q: Does the HSA work on a flat road?
YES: Replace the G and yaw rate sensor. Then go to Step 6.
NO: Go to Step 6.

STEP 6. Retest the system.
Check if the HSA works on a flat road with one occupant (driver) only in the vehicle.
Q: Does the HSA work on a flat road?
YES: Return to Step 2.
NO: This diagnosis is complete.