Inspection Procedure 5

Inspection Procedure 5: The activated theft-alarm siren sounds even though no faulty operation is made.

CAUTION:
Before replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.














TECHNICAL DESCRIPTION (COMMENT)

If the activated theft-alarm siren sounds even though no faulty operation is made, the theft-alarm siren may not be able to receive the signal from the ETACS-ECU via the LIN cutoff control unit.
NOTE:
The theft alarm siren may be sounding by false alarm. Investigate what kind of situation the theft-alarm siren sounded under. Check if there was any condition that caused false alarm.

TROUBLESHOOTING HINTS

- theft-alarm siren may be defective
- LIN cutoff control unit may be defective
- The ETACS-ECU may be defective
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector

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 (Vehicles with CAN communication system)

STEP 1. Vehicle status check when theft-alarm siren is sounding

(1)Since it is suspected that the theft-alarm has sounded accidentally, investigate whether the vehicle is under the situation below. Repair if an abnormality is found.

- The windows and sunroof are open.
- Some moving accessories are fitted in the vehicle.
- The interior equipment has been modified before a malfunction occurs.

(2)Set the sensitivity level of theft-alarm sensor to Level 4 by using the customization function.

(3)Check if the theft-alarm siren sounds during the status of "Ready to be triggered"
even though no faulty operation is made.

Q. Is the check result normal?

YES Go to Step 2
NO The diagnosis is complete.
STEP 2. Using scan tool MB991958, read the ETACS-ECU diagnostic trouble code.

Check if DTC is set to the ETACS-ECU.

CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.





Connect scan tool MB991958. Refer to "How to connect scan tool (M.U.T.-III) Reading and Clearing Diagnostic Trouble Codes."
(1)Turn the ignition switch to the "ON" position.
(2)Check whether the ETACS-ECU DTC is set.
(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the DTC set?

YES Diagnose the ETACS-ECU (Refer to Electronic Time and Alarm Control System (ETACS)).

NO Go to Step 3.

STEP 3. LIN cutoff control unit check

Check for continuity of the LIN cutoff control unit.(Refer to LIN Cutoff Control Unit Inspection.)

Q. Is the check result normal?

YES Go to Step 4.
NO Replace LIN cutoff control unit.
STEP 4. Check ETACS-ECU connector C-312, C-301 and LIN cutoff control unit C-140 for loose, corroded or damaged terminals, or terminals pushed back in the connector

Q. Is the check result normal?

YES Go to Step 5.
NO Repair the defective connector.
STEP 5. Check the Wiring harness between ETACS-ECU connector 301 (terminal No. 13) and LIN cutoff control unit C-140 (terminal No. 3).

Check the signal line for open circuit and short circuit.

Q. Is the check result normal?

YES Go to Step 6.
NO Repair the wiring harness.
STEP 6. Check the Wiring harness between ETACS-ECU connector 312 (terminal No. 9) and LIN cutoff control unit C-140 (terminal No. 8).

Check the signal line for short circuit.

NOTE:
Also check intermediate connector C-130 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-130 is damaged, repair or replace the connector as described in Harness Connector Inspection Harness Connector Inspection.

Q. Is the check result normal?

YES Go to Step 7.
NO Repair the wiring harness.
STEP 7. Retest the theft-alarm system.

Check if the activated theft-alarm siren sounds even though no faulty operation is made.

Q. Is the check result normal?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the ETACS-ECU.