Inspection Procedure N-2

Theft-alarm System: Horn does not Sound when the Theft-alarm is Triggered.

Theft-alarm Horn Drive Circuit:

Horn Drive Circuit Part 1:

Horn Drive Circuit Part 2:

CIRCUIT OPERATION
When the theft-alarm system is triggered, the ETACS-ECU sounds the theft-alarm horn and all the vehicle horns.

TECHNICAL DESCRIPTION (COMMENT)
If the theft-alarm horn and the vehicle horns do not sound when the theft-alarm system is triggered, the ETACS-ECU may be defective.

TROUBLESHOOTING HINTS
- The theft-alarm horn may be defective
- The horn may be defective
- The theft-alarm horn relay may be defective
- The 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 Tool:
- MB991223: Test Harness Set

STEP 1. Check which horn is defective.
Check which horn does not sound when the theft-alarm system is triggered.

Q: Which horn does not sound?

theft-alarm horn: Go to Step 2.
horn: Go to Step 12.
theft-alarm horn and all vehicle horns: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 2. Check the theft-alarm horn.




1. Remove the horn.




2. Connect the battery as shown, and check that the theft-alarm horn sounds.

Q: Does the theft-alarm horn sound?

YES: Go to Step 3.

NO: Replace the theft-alarm horn. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 3. Check theft-alarm horn relay connector A-06X for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is theft-alarm horn relay connector A-06X in good condition?

YES: Go to Step 4.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.







STEP 4. Check the theft-alarm horn relay.

Q: Is the theft-alarm horn relay normal?

YES: Go to Step 5.

NO: Replace the theft-alarm horn relay. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 5. Check the fusible link 4. line of the power supply circuit to the theft-alarm horn relay. Measure the voltage at theft-alarm horn relay connector A-06X.




1. Disconnect theft-alarm horn relay connector A-06X and measure the voltage available at the relay box side of the connector.




2. Measure the voltage between terminal 1, 2 and 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 7.

NO: Go to Step 6.




STEP 6. Check the wiring harness between theft-alarm horn relay connector A-06X (terminals 1 and 2) and fusible link (4).

Q: Is the wiring harness between theft-alarm horn relay connector A-06X (terminals 1 and 2) and fusible link (4) in good condition?

YES: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 7. Check theft-alarm horn connector A-25 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is theft-alarm horn connector A-25 in good condition?

YES: Go to Step 8.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.







STEP 8. Check the wiring harness between theft-alarm horn relay connector A-06X (terminal 4) and theft-alarm horn connector A-25 (terminal 1).

Q: Is the wiring harness between horn relay connector A-06X (terminal 4) and theft-alarm horn connector A-25 (terminal 1) in good condition?

YES: Go to Step 9.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 9. Check ETACS-ECU connector C-117 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ETACS-ECU connector C-117 in good condition?

YES: Go to Step 10.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.













STEP 10. Check the wiring harness between theft-alarm horn relay connector A-06X (terminal 3) and ETACS-ECU connector C-117 (terminal 40).

NOTE: Also check intermediate connector C-89 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-89 is damaged, repair or replace the damaged component(s) as described in Harness Connector Inspection.

Q: Is the wiring harness between theft-alarm horn relay connector A-06X (terminal 3) and ETACS-ECU connector C-117 (terminal 40) in good condition?

YES: Go to Step 11.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 11. Check the fit of the theft-alarm horn.

NOTE: The theft-alarm horn is grounded to the vehicle body via its mounting bolt.

Q: Is the theft-alarm horn installed correctly?

YES: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

NO: Install the theft-alarm horn correctly. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 12. Check horn relay connector A-05X for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is horn relay connector A-05X in good condition?

YES: Go to Step 13.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.







STEP 13. Check the horn relay.

Q: Is the horn relay normal?

YES: Go to Step 14.

NO: Replace the horn relay. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 14. Check the battery power supply circuit to the horn relay. Measure the voltage at horn relay connector A-05X.




1. Disconnect horn relay connector A-05X, and measure at the relay box side.




2. Measure the voltage between terminal 1, 2 and 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 16.

NO: Go to Step 15.




STEP 15. Check the wiring harness between horn relay connector A-05X (terminals 1 and 2) and the battery.

Q: Is the wiring harness between horn relay connector A-05X (terminals 1 and 2) and the battery in good condition?

YES: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 16. Check horn connector A-27 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are horn relay connector A-05X and horn connector A-27 in good condition?

YES: Go to Step 17.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.







STEP 17. Check the wiring harness between horn relay connector A-05X (terminal 4) and horn connector A-27 (terminal 1).

Q: Is the wiring harness between horn relay connector A-05X (terminal 4) and horn connector A-27 (terminal 1) in good condition?

YES: Go to Step 18.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.




STEP 18. Check ETACS-ECU connector C-117 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ETACS-ECU connector C-117 in good condition?

YES: Go to Step 19.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.










STEP 19. Check the wiring harness between horn relay connector A-05X (terminal 3) and ETACS-ECU connector C-117 (terminal 44).

NOTE: Also check intermediate connector C-89 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-89 is damaged, repair or replace the damaged component(s) as described in Harness Connector Inspection.

Q: Is the wiring harness between horn relay connector A-05X (terminal 3) and ETACS-ECU connector C-117 (terminal 44) in good condition?

YES: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

NO: The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 20. Check the horn.




1. Remove the horn.




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

Q: Is the horn normal?

YES: Go to Step 21.

NO: Replace the defective horn. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

STEP 21. Check the fit of the horn.
Check that the horn is installed correctly.

NOTE: The horn is grounded to the vehicle body via its mounting bolt.

Q: Is the horn installed correctly?

YES: Replace the ETACS-ECU. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.

NO: Install the horn correctly. All the vehicle horn (including the theft-alarm horn) should sound when the theft-alarm system is triggered.