Inspection Procedure 4

Inspection Procedure 4: Horn (HIGH or LOW) does not sound while the theft-alarm system is triggered.

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






















TECHNICAL DESCRIPTION (COMMENT)

If horns do not sound, the horn input signal circuit or the ETACS-ECU may be defective.

TROUBLESHOOTING HINTS

- Horns may be defective
- Horn relay 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:

- MB992006: Extra fine probe
- MB991223: Harness set
- 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. Using scan tool MB991958, read the diagnostic trouble code.

Check if DTC is set to the ETACS-ECU.





(1)
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."
(2)Turn the ignition switch to the "ON" position.
(3)Check whether the ETACS-ECU related DTC is set.
(4)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 2.

STEP 2. Check horn relay connector A-16X for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is horn relay connector A-16X in good condition?

YES Go to Step 3.
NO Repair the damaged parts.
STEP 3. Check the horn relay.

Refer to Theft Alarm Inspection.

Q. Is the horn relay in good condition

YES Go to Step 4.
NO Replace the theft-alarm horn relay.
STEP 4. Measure the voltage at horn relay A-16X.

(1)Remove the relay, and measure at the relay box side.





(2)Measure the voltage between horn relay connector A-16X (terminal No. 2,4) and the body ground.

- The voltage should measure approximately 12 volts (battery positive voltage).

Q. Is the measured voltage approximately 12 volts (battery positive voltage)?

YES Go to Step 6.

NO Go to Step 5.

STEP 5. Check the Wiring harness between horn relay connector A-16X
(terminal No. 2,4) and fusible link (36).

Check the power supply line for open circuit and short circuit.

Q. Is the check result normal?

YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Repair the wiring harness between horn relay connector A-12X and fusible link
(36).
STEP 6. Check ETACS-ECU connector C-312 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is ETACS-ECU connector C-312 in good condition?

YES Go to Step 7.
NO Repair the damaged parts.
STEP 7. Check the Wiring harness between theft-alarm horn relay connector A-16X (terminal No. 1) and ETACS-ECU connector C-312 (terminal No. 11).

Check the output lines for open circuit and short circuit.

Q. Is the check result normal?

YES Go to Step 8.
NO Repair the wiring harness between horn relay connector A-12X and ETACS-ECU connector C-312.
STEP 8. Check horn (HIGH) connector A-44 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is Horn (HIGH) connector A-44 in good condition?

YES Go to Step 9.
NO Repair the damaged parts.
STEP 9. Check the Wiring harness between horn (HIGH) connector A-44
(terminal No. 1) and horn relay connector A-16X (terminal No. 3).

Check the output lines for open circuit and short circuit.

Q. Is the check result normal?

YES Go to Step 10.
NO Repair the wiring harness between horn (HIGH) connector A-44 and horn relay connector A-16X.
STEP 10. Check the horn (HIGH) work normally.





Connect the battery as shown, and verify that the horn sounds.

Q. Is the check result normal?

YES Go to Step 11.

NO Replace the horn (HIGH). go to Step 14.

STEP 11. Check horn (LOW) connector A-51 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is Horn (LOW) connector A-51 in good condition?

YES Go to Step 12.
NO Repair the damaged parts.
STEP 12. Check the Wiring harness between horn (LOW) connector A-51
(terminal No. 1) and horn relay connector A-16X (terminal No. 3).

Check the output lines for open circuit and short circuit.

Q. Is the check result normal?

YES Go to Step 13.
NO Repair the wiring harness between horn (LOW) connector A-51 and horn relay connector A-16X.
STEP 13. Check the horn (LOW) work normally.





Connect the battery as shown, and verify that the horn sounds.

Q. Is the check result normal?

YES Go to Step 14.

NO Replace the horn (LOW). go to Step 14.

STEP 14.Retest the theft-alarm system.

Q. Does the theft-alarm system work normally?

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