Inspection Procedure 2: With the Parking Brake Released, the Brake Warning Light Remains Illuminated (ABS Warning Light Is Off)
Inspection Procedure 2: With the parking brake released, the brake warning light remains illuminated (ABS warning light is turned off).
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.
^ Whenever the ECU is replaced, ensure that the communication circuit is normal.
CIRCUIT OPERATION
^ When the parking brake switch is turned ON, the combination meter terminal No. 4 is grounded, and then the brake warning light is illuminated.
^ When the brake fluid level drop is detected, the brake fluid level switch is turned from ON to OFF. ETACS-ECU monitors the brake fluid level switch, and gives an instruction via the CAN bus line to the combination meter to illuminate the brake warning light.
PROBABLE CAUSES
^ The brake pad thickness is at the limit value or less.
^ The brake fluid amount is at the "LOWER" level or lower.
^ Poor adjustment of the parking brake lever
^ Damaged wiring harness and connectors
^ Parking brake switch malfunction
^ Brake fluid level switch malfunction
^ Combination meter malfunction
^ ETACS-ECU malfunction
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. Using scan tool MB991958, diagnose the CAN bus lines.
Using scan tool MB991958, diagnose the CAN bus lines.
Q: Is the check result normal?
YES: Go to Step 2.
NO: Repair the CAN bus lines. (Refer to Troubleshooting Can Bus Diagnostics Table.)
STEP 2. Scan tool diagnostic trouble code for other systems
Using scan tool MB991958, check if the diagnostic trouble code is set in the combination meter and ETACS-ECU.
Q: Is any DTC set?
YES: Carry out the diagnosis for the DTC.
NO: Go to Step 3.
STEP 3. Brake fluid level check
Check that the brake fluid is filled up to the "MIN" level or higher.
Q: Is the check result normal?
YES: Go to Step 5.
NO: Go to Step 4.
STEP 4. Brake pad check
Q: Is the check result normal?
YES: Fill the brake fluid up to the "MAX" level. Then go to Step 18.
NO: Replace the brake pad. Then, go to Step 18.
STEP 5. Brake fluid level switch check
Refer to On-vehicle Service, Brake Fluid Level Switch Check Testing and Inspection.
Q: Is the check result normal?
YES: Go to Step 6.
NO: Replace the reservoir tank assembly. Then, go to Step 18.
STEP 6. Connector check: C-312 ETACS-ECU connector, A-09 brake fluid level switch connector
Q: Is the check result normal?
YES: Go to Step 7.
NO: Repair the defective connector.
STEP 7. Voltage measurement at A-09 brake fluid level switch connector
1) Disconnect the connector, and measure at the wiring harness side.
2) Turn the ignition switch to the ON position.
3) Measure the voltage between the terminal No.2 and the body ground.
OK: Battery positive voltage
Q: Is the check result normal?
YES: Go to Step 9.
NO: Go to Step 8.
STEP 8. Voltage measurement at C-312 ETACS-ECU connector
CAUTION:
Keep the C-312 ETACS-ECU connector remain connected, then disconnect A-09 brake fluid level switch connector.
1) Turn the ignition switch to the ON position.
2) Measure the voltage between the terminal No. 1 and the body ground by backprobing.
OK: Approximately battery voltage
Q: Is the check result normal?
YES: Repair the wiring harness between C-312 ETACS-ECU connector terminal No. 1 and A-09 brake fluid level switch connector terminal No. 2.
NO: Replace the ETACS-ECU. Then go to Step 18.
STEP 9. Wiring harness check: Between A-09 brake fluid level switch connector and the body ground
Check for an open circuit in the wiring harness between A-09 brake fluid level switch connector terminal No. 1 and the body ground.
Q: Is the check result normal?
YES: Go to Step 10.
NO: Repair the wiring harness.
STEP 10. Parking brake lever stroke check
Q: Is the check result normal?
YES: Go to Step 11.
NO: Adjust the parking brake lever stroke. Then, go to Step 18.
STEP 11. Parking brake switch check
Q: Is the check result normal?
YES: Go to Step 12.
NO: Replace the parking brake switch. Then, go to Step 18.
STEP 12. Connector check: C-122 parking brake switch connector
Q: Is the check result normal?
YES: Go to Step 13.
NO: Repair the defective connector.
STEP 13. Voltage measurement at C-122 parking brake switch connector
1) Disconnect the connector, and measure at the wiring harness side.
2) Turn the ignition switch to the ON position.
3) Measure the voltage between the terminal No. 1 and the body ground.
OK: Battery positive voltage
Q: Is the check result normal?
YES: Go to Step 17.
NO: Go to Step 14.
STEP 14. Connector check: C-04 combination meter connector, C-23 intermediate connector
Q: Is the check result normal?
YES: Go to Step 15.
NO: Repair the defective connector.
STEP 15. Voltage measurement at C-04 combination meter connector
1) Release the parking brake lever (not operated).
2) Turn the ignition switch to the ON position.
3) Without disconnecting the connector, measure the voltage between the terminal No. 4 and the body ground by backprobing.
OK: Battery positive voltage
Q: Is the check result normal?
YES: Go to Step 17.
NO: Go to Step 16.
STEP 16. Wiring harness check: Between C-04 combination meter connector and C-122 parking brake switch connector
Check for a short circuit in the wiring harness between C-04 combination meter connector terminal No. 4 and C-122 parking brake switch connector terminal No. 1.
Q: Is the check result normal?
YES: Go to Step 17.
NO: Repair the wiring harness.
STEP 17. Retest the system.
Q: Does the brake warning light turn ON and OFF normally according to the parking brake lever operation?
YES: Intermittent malfunction.
NO: Replace the combination meter assembly. Then, go to Step 18.
STEP 18. Retest the system.
Q: Does the brake warning light turn ON and OFF normally according to the parking brake lever operation?
YES: The procedure is complete.
NO: Return to Step 1.