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Test No. 7: While System Is In Alarming Condition, Horns Do Not Sound; Or When System Is Not Set, Horns Sound

WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Three different horns are used when theft deterrent system is in alarming condition. Theft deterrent horn is located in right rear corner of engine compartment. Two standard horns are mounted at each side of vehicle, just behind front bumper. Theft deterrent horn is entirely controlled by theft deterrent ECU. Standard horns are controlled either by pushing horn switch or by body control ECU when theft deterrent system has been activated. For testing procedures covering standard horns and horn system, see BODY CONTROL SYSTEMS - AVALON article under COMMUNICATION DEVICES in ACCESSORIES & EQUIPMENT.
  1. Turn ignition off. Disconnect theft deterrent ECU 26-pin electrical harness connector T4. Using a DVOM, measure voltage between theft deterrent ECU 26-pin electrical harness connector T4 terminal No. 24 (Black/Red wire) and good vehicle ground point. See Figure. If voltage is 10-14 volts, go to next step. If voltage is not 10-14 volts, check and repair power supply circuit (Black/Red wire) between theft deterrent ECU and battery. See ANTI-THEFT in SYSTEM WIRING DIAGRAMS article. After repairs have been made, perform confirmation test. See CONFIRMATION TEST .
  2. Remove theft deterrent horn, and disconnect Black single-pin electrical harness connector. See Figure. Using a DVOM, measure voltage between theft deterrent horn electrical harness connector and good vehicle ground point. If voltage is 10-14 volts, go to next step. If voltage is not 10-14 volts, check and repair power supply circuit (White wire) between theft deterrent ECU and battery. See ANTI-THEFT in SYSTEM WIRING DIAGRAMS article. After repairs have been made, perform confirmation test. See CONFIRMATION TEST .
  3. Using fused jumper wires, connect positive voltage to terminal of theft deterrent horn and ground the body of the horn. Horn should operate. If horn operates, go to next step. If horn does not operate, replace horn. After repairs have been made, perform confirmation test. See CONFIRMATION TEST .
  4. Disconnect theft deterrent ECU 26-pin electrical harness connector T4 and theft deterrent horn Black single-pin electrical harness connector. Check White wire between theft deterrent ECU 26-pin electrical harness connector T4 terminal No. 25 and theft deterrent horn Black single-pin electrical harness connector. See ANTI-THEFT in SYSTEM WIRING DIAGRAMS article. If wiring harnesses and electrical connectors are okay, go to next step. If wiring harnesses or electrical connectors are defective, repair as necessary. After repairs have been made, perform confirmation test. See CONFIRMATION TEST .
  5. Check theft deterrent ECU ground circuits. See ANTI-THEFT in SYSTEM WIRING DIAGRAMS article. If ground circuits are faulty, repair and retest system. If ground circuits are okay, substitute original theft deterrent ECU with a known-good unit and recheck system operation. If system operates properly, original theft deterrent ECU was defective. If system still does not operate properly, perform theft deterrent ECU pin voltage/resistance checks. See Figure. If voltage/resistance values are okay, replace theft deterrent ECU. After repairs have been made, perform confirmation test. See CONFIRMATION TEST .
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