Inspection Procedure 3: Brake Warning Light Stays On With the Parking Brake Lever Released

Inspection Procedure 3: Brake Warning Light Stays ON with the Parking Brake Lever Released.








CAUTION
^ If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines.
^ Whenever ECU is replaced, ensure that the CAN bus lines are 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 illuminates.
^ When reduction of the brake fluid amount is detected, the brake fluid level switch is turned from ON to OFF. ETACS-ECU monitors the brake fluid level switch, and instructs the combination meter via the CAN bus line to illuminate the brake warning light.

COMMENTS ON TROUBLE SYMPTOM
This may be caused by the ground fault in the parking brake switch circuit and the open circuit in the brake fluid level switch circuit.

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
^ Malfunction of ETACS-ECU

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. M.U.T.-III CAN bus diagnostics
Use scan tool to diagnose the CAN bus lines.

Q: Is the check result normal?
YES: Go to Step 2.
NO: Repair the CAN bus lines. On completion, go to Step 2.

STEP 2. DTC check after resetting CAN bus lines
Use scan tool to check that the DTC 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

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: A-06 brake fluid level switch connector, C-312 ETACS-ECU connector

Q: Is the check result normal?
YES: Go to Step 7.
NO: Repair the damaged connector.

STEP 7. Measure the voltage at A-06 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. 1 and the body ground.
OK: Battery positive voltage

Q: Is the check result normal?
YES: Go to Step 10.
NO: Go to Step 8.

STEP 8. Measure the voltage at the C-312 ETACS-ECU connector.

CAUTION
With the C-312 ETACS-ECU connector kept connected, disconnect the A-06 brake fluid level switch connector.

1) Turn the ignition switch to the ON position.
2) Measure the voltage between terminal No.1 and the body ground by backprobing.
OK: Battery positive voltage

Q: Is the check result normal?
YES: Go to Step 9.
NO: Replace the ETACS-ECU. Then go to Step 18.

STEP 9. Wiring harness check: between A-06 brake fluid level switch connector and C-312 ETACS-ECU connector
Check for open circuit in the harness wire between A-06 brake fluid level switch connector terminal No.1 and C-312 ETACS-ECU connector terminal No.1.

Q: Is the check result normal?
YES: Go to Step 16.
NO: Repair the wiring harness. Then go to Step 18.

STEP 10. Wiring harness check: between A-06 brake fluid level switch connector and body ground
Check for open circuit in the harness wire between A-06 brake fluid level switch connector terminal No.2 and body ground.

Q: Is the check result normal?
YES: Go to Step 11.
NO: Repair the wiring harness.

STEP 11. Parking brake lever stroke check

Q: Is the check result normal?
YES: Go to Step 12.
NO: Adjust the parking brake lever stroke. Then go to Step 18.

STEP 12. Parking brake switch check

Q: Is the check result normal?
YES: Go to Step 13.
NO: Replace the parking brake switch. Then go to Step 18.

STEP 13. Connector check: C-117 parking brake switch connector

Q: Is the check result normal?
YES: Go to Step 14.
NO: Repair the damaged connector.

STEP 14. Measure the voltage at C-117 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 15.

STEP 15. Connector check: C-04 Combination meter connector, C-21 intermediate connector

Q: Is the check result normal?
YES: Go to Step 16.
NO: Repair the defective connector.

STEP 16. Wiring harness check: between the C-04 combination meter connector and the C-117 parking brake switch connector
Check for short circuit in the harness wire between the C-04 combination meter connector terminal No.4 and the C-117 parking brake switch connector terminal No.1.

Q: Is the check result normal?
YES: Go to Step 17.
NO: Repair the wiring harness. Then go to Step 18.

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.