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Inspection Procedure M-2

INSPECTION PROCEDURE M-2: Theft-alarm System: Horn does not sound when the theft-alarm is triggered.

Horn Drive Circuit Part 1:




Horn Drive Circuit Part 2:






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

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

TROUBLESHOOTING HINTS
- Trouble in input signal system
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector
- The horn may be defective
- The horn relay may be defective
- The ETACS-ECU may be defective

DIAGNOSIS
Required Special Tool:
- MB991223: Harness Set
- MB992006: Extra Fine Probe

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?

All the horns : Go to Step 2.
Horn (high) only : Go to Step 8.
Horn (low) only : Go to Step 11.







STEP 2. Check the horn relay.

Q: Is the horn relay in good condition?

YES: Go to Step 3.

NO: Replace the horn relay.




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

Q: Is 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. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.

STEP 4. Check the battery power supply circuit to the horn relay. Measure the voltage at horn relay connector A-06X.

CAUTION: The top and bottom of the horn relay connector are difficult to identify. Prior to inspection, confirm the triangle mark on the relay box.




1. Disconnect 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 and ground, and also between terminal 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 6.

NO: Go to Step 5.




STEP 5. Check the wiring harness between horn relay connector A-06X (terminals 1 and 2) and the battery.

Q: Is the wiring harness between relay connector A-06X (terminals 1 and 2) and the battery in good condition?

YES: No action is necessary and testing is complete.

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. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.




STEP 6. Check ETACS-ECU connector C-217 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ETACS-ECU connector C-217 in good condition?

YES: Go to Step 7.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.







STEP 7. Check the wiring harness between horn relay connector A-06X (terminal 3) and ETACS-ECU connector C-217 (terminal 44).






NOTE: Also check intermediate connector C-31 and joint connector C-103 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-31 or joint connector C-103 are damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Is the wiring harness between horn relay connector A-06X (terminal 3) and ETACS-ECU connector C-217 (terminal 44) in good condition?

YES: Replace the ETACS-ECU.

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. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.




STEP 8. Check horn (high) connector A-19 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is horn (high) connector A-19 in good condition?

YES: Go to Step 9.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Verify that the horn sounds normally.




STEP 9. Check the horn (high).
Connect the battery as shown, and verify that the horn sounds.

Q: Is the horn normal?

YES: Go to Step 10.

NO: Replace the horn (high). Verify that all the vehicle horns should sound when the theft-alarm system is triggered.







STEP 10. Check the wiring harness between horn relay connector A-06X (terminal 4) and horn (high) connector A-19 (terminal 1).

Q: Is the wiring harness between horn relay connector A-06X (terminal 4) and horn (high) connector A-19 (terminal 1) in good condition?

YES: No action is necessary and testing is complete.

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. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.




STEP 11. Check horn (low) connector A-01 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is horn (low) connector A-01 in good condition?

YES: Go to Step 12.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Verify that the horn sounds normally.




STEP 12. Check the horn (low).
Connect the battery as shown, and verify that the horn sounds.

Q: Is the horn normal?

YES: Go to Step 13.

NO: Replace the horn (low). Verify that all the vehicle horns should sound when the theft-alarm system is triggered.







STEP 13. Check the wiring harness between horn relay connector A-06X (terminal 4) and horn (low) connector A-01 (terminal 1).

Q: Is the wiring harness between horn relay connector A-06X (terminal 4) and horn (low) connector A-01 (terminal 1) in good condition?

YES: No action is necessary and testing is complete.

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. Verify that all the vehicle horns should sound when the theft-alarm system is triggered.
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