Inspection Procedure 15: HSA (Hill Start Assist) Does Not Work
Inspection Procedure 15: HSA (Hill Start Assist) does not work.
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 Diagnosis 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
^ The slope gradient may be low.
^ The vehicle is not completely stationary.
^ A failure may have occurred in the calibration of the G and yaw rate sensor or brake fluid pressure sensor.
^ The parking brake switch may be seized, which causes the HSA to fail to start the operation.
^ A problem (noise interference) may have occurred in the CAN bus line, resulting in an improper communication with ASC-ECU or each ECU.
NOTE:
^ The HSA does not work even when the wheel speed sensor outputs pulse (vehicle moved) while the vehicle is parked.
^ The HSA is affected by the loading conditions and vehicle posture at the occurrence of phenomenon. When checking the HSA operation in actual driving, carry out the check on the vehicle with one occupant (driver) only.
PROBABLE CAUSES
^ Improper installation of the G and yaw rate sensor
^ G and yaw rate sensor malfunction
^ Calibration failure of the brake fluid pressure sensor
^ Seizure of the parking brake switch
^ Malfunction of wheel speed sensor
^ Malfunction of hydraulic unit (integrated with ASC-ECU)
^ Wiring harness or connector failure of CAN bus line
^ 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
^ MB991997: ASC check harness
STEP 1. HSA operation check
Check if the HSA works with one occupant (driver) only in the vehicle.
Q: Is the check result normal?
YES: This diagnosis is complete.
NO: Go to Step 2.
STEP 2. Parking brake check
With the parking brake not pulled, check if the brake warning light is illuminated.
Q: Is the brake warning light illuminated with the parking brake not pulled?
YES: Carry out the Inspection procedure 3 "Brake Warning light Stays ON with the Parking Brake Lever Released (ABS warning light is OFF)."(Refer to Inspection Procedure 3: Brake Warning Light Stays on With the Parking Brake Lever Released.)
NO: Go to Step 3.
STEP 3. Using scan tool MB991958, diagnose the CAN bus line.
Use scan tool to diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 4.
NO: Repair the CAN bus lines. (Refer to Troubleshooting Symptom Chart.) Then go to Step 14.
STEP 4. Using scan tool MB991958, check the DTC
Use scan tool MB991958 to check the DTC for the ASC system.
Q: Is the DTC set?
YES: Carry out the diagnosis for the diagnostic trouble code (Refer to Diagnostic Trouble Code Descriptions).
NO: Go to Step 5.
STEP 5. Using scan tool MB991958, check the data list
Check the following service data (Refer to Scan Tool Testing and Procedures).
^ Item 120: Parking brake switch (Input)
Q: Is the check result normal?
YES: Go to Step 6.
NO: Carry out the Inspection procedure 3 "Brake Warning light Stays ON with the Parking Brake Lever Released (ABS warning light is OFF)."(Refer to Inspection Procedure 3: Brake Warning Light Stays on With the Parking Brake Lever Released..), and then go to Step 14.
STEP 6. Using scan tool MB991958, check the data list
Check the following service data (Refer to Scan Tool Testing and Procedures).
^ Item 09: G sensor
^ Item 12: Yaw rate sensor
Q: Is the check result normal?
YES: Go to Step 10
NO: Go to Step 7
STEP 7. Connector check: A-51 ASC-ECU connector, C-137 G and yaw rate sensor
Q: Is the check result normal?
YES: Go to Step 8.
NO: Repair the connector, and then go to Step 14.
STEP 8. Check the harness wire between C-137 G and yaw rate sensor connector terminal No. 2, 3 and A-51 ASC-ECU connector No. 18, 19.
^ Check the communication lines for open circuit and short circuit.
Q: Is the check result normal?
YES: Go to Step 9.
NO: Repair the wiring harness, and then go to Step 14.
STEP 9. 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 10
NO: Reinstall the G and yaw rate sensor correctly and then go to Step 14.
STEP 10. Using scan tool MB991958, check the data list
Check the following service data (Refer to Scan Tool Testing and Procedures).
^ Item 10: Master cylinder pressure
Q: Is the check result normal?
YES: Go to Step 11
NO: Carry out the calibration of the brake fluid pressure sensor. Then go to Step 12
STEP 11. Using scan tool MB991958, check the DTC the other system.
Use scan tool MB991958 to check that the diagnostic trouble code is set in the TS-SST-ECU.
Q: Is the diagnostic trouble code set?
YES: Carry out the diagnosis for the diagnostic trouble code. (Refer to Diagnosis Troubleshooting Diagnostic Trouble Code Descriptions)
NO: Go to Step 12.
STEP 12. Retest the system.
Check if the HSA works with one occupant (driver) only in the vehicle.
Q: Is the check result normal?
YES: If a trouble is solved, it is determined that there is an intermittent malfunction such as poor engaged connector(s) or open circuit.
NO: Replace the G and yaw rate sensor. Then go to Step 13.
STEP 13. Retest the system.
Check if the HSA works with one occupant (driver) only in the vehicle.
Q: Is the check result normal?
YES: This diagnosis is complete.
NO: Replace the hydraulic unit (ASC-ECU) Then go to Step 14.
STEP 14. Retest the system.
Check if the HSA works with one occupant (driver) only in the vehicle.
Q: Is the check result normal?
YES: This diagnosis is complete.
NO: Return to Step 1.