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Inspection Procedure 3: Theft-alarm horn does not sound while the theft-alarm system is triggered.
 
 
cautionBefore replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
 
 
 
 
TECHNICAL DESCRIPTION (COMMENT)
If theft-horn does not sound, the theft-horn input signal circuit or the ETACS-ECU may be defective.
 
 
TROUBLESHOOTING HINTS
  • Theft-alarm horn may be defective
  • Theft-alarm 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:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Using scan tool MB991958, read the diagnostic trouble code.
Check if DTC is set in the ETACS-ECU.
(1)
cautionTo 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 too (M.U.T.-III) ."
(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.
Is the DTC set?
Diagnose the ETACS-ECU. Refer to .
Go to Step 2.
 
STEP 2. Check the theft-alarm horn work normally.
Connect the battery as shown, and verify that the horn sounds.
Does horn (HI) work normally?
Go to Step 3.
Replace the horn (HI). Then, go to Step 4.
 
STEP 3. Check theft-alarm horn relay connector A-21X for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Is theft-alarm horn relay connector A-21X in good condition?
Go to Step 4.
Repair the damaged parts.
 
STEP 4. Check the theft-alarm horn relay.
Refer to .
Is the theft-alarm horn relay in good condition
Go to Step 5.
Replace the theft-alarm horn relay.
 
STEP 5. Measure the voltage at theft-alarm horn relay A-21X.
(1) Remove the relay, and measure at the relay box side.
(2) Measure the voltage between theft-alarm horn relay connector A-21X (terminal No. 1,4) and the body ground.
  • The voltage should measure approximately 12 volts (battery positive voltage).
Is the measured voltage approximately 12 volts (battery positive voltage)?
Go to Step 7.
Go to Step 6.
 
STEP 6. Check the Wiring harness between theft-alarm horn relay connector A-21X (terminal No. 1,4) and fusible link (36).
Check the power supply lines for open circuit and short circuit.
Is the check result normal?
The trouble can be an intermittent malfunction (Refer to GROUP 00, How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the wiring harness between theft-alarm horn relay connector A-21X and fusible link (36).
 
STEP 7. Check theft-alarm horn connector A-68 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Is theft-alarm horn connector A-68 in good condition?
Go to Step 8.
Repair the damaged parts.
 
STEP 8. Check the Wiring harness between theft-alarm horn connector A-68 (terminal No. 1) and theft-alarm horn relay connector A-21X (terminal No. 3).
Check the output line for open circuit and short circuit.
noteBefore the wiring harness check, check intermediate connector A-66, and then repair them if necessary.
Is the check result normal?
Go to Step 9.
Repair the wiring harness between theft-alarm horn connector A-68 and theft-alarm horn relay connector A-21X.
 
STEP 9. Check ETACS-ECU connector C-410 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Is ETACS-ECU connector C-410 in good condition?
Go to Step 10.
Repair the damaged parts.
 
STEP 10. Check the Wiring harness between theft-alarm horn relay connector A-21X (terminal No. 2) and ETACS-ECU connector C-410 (terminal No. 15).
Check the output lines for open circuit and short circuit.
Is the check result normal?
Go to Step 11.
Repair the wiring harness between theft-alarm horn relay connector A-21X and ETACS-ECU connector C-410.
 
STEP 11. Replace theft-alarm horn.
(1) Replace the theft-alarm horn.
Does the theft-alarm work normally?
he trouble can be an intermittent malfunction (Refer to GROUP 00, How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).
Replace the ETACS-ECU.