Test No. 46: Horns Operate All The Time

NOTE: Three different horns are used. One theft-deterrent horn is located on passenger's strut tower in engine compartment. Two standard horns are mounted at each side of vehicle, just behind the front bumper. Theft-deterrent horn is entirely controlled by theft-deterrent Electronic Control Unit (ECU). Standard horns are controlled either by pushing horn switch or by body ECU when theft-deterrent system has been activated. For testing procedures covering theft-deterrent horn and theft-deterrent system, see ANTI-THEFT SYSTEMS - AVALON article.

Check operation of horn relay by consulting wiring diagram to ensure relay is not stuck closed. See WIRING DIAGRAMS in STEERING COLUMN SWITCHES - CARS article. Horn relay is located in fuse/relay box at driver's side front corner of engine compartment. See Figure. If horn relay is okay, go to next step. If horn relay is defective, replace horn relay and recheck horn operation.
Check wiring harness and electrical connectors between body ECU and horn relay, and between horn switch and the horn relay for short to ground that would cause horn relay to operate. Also, check wiring harness and electrical connectors between horn relay and the horn switch for short to voltage which would cause the horn to operate. See WIRING DIAGRAMS in STEERING COLUMN SWITCHES - CARS article. Body ECU is located at driver's side of instrument panel on the fuse/relay box. See Figure. Electrical connector B4 (25-pin) and electrical connector B5 (25-pin) are located at each side of body ECU and a 12-pin electrical connector at rear of body ECU. See Figure. Repair wiring harness or electrical connectors as necessary and recheck horn operation.