2004 Lexus SC 430FACTORY OEM SERVICE PROCEDURE

Horn System: Inspection

  1. INSPECT HORN BUTTON ASSYΒ 
    1. Check that no continuity exists between terminal 6 of the connector and body ground.
    2. Check that continuity exists between terminal 6 of the connector and body ground when the horn contact plate is pressed against the steering spoke assembly.

    If the continuity is not as specified, repair or replace the steering wheel or wire harness as necessary.

    Fig 1: Identifying Horn Button Assy Connector Terminals
    G03479661Courtesy of Β© TOYOTA, LICENSE AGREEMENT TMS1002
  2. INSPECT RELAY (HORN)Β 
    1. Remove the HORN relay from the engine room R/B.
    2. Measure the HORN relay resistance.
      Fig 2: Identifying Horn Relay Terminals
      G03479662Courtesy of Β© TOYOTA, LICENSE AGREEMENT TMS1002

    Standard:Β 

    HORN RELAY RESISTANCE CHART

    Tester Connection Specified Condition
    3 - 5 10 kΞ© or higher
    3 - 5 Below 1 Ξ© (when battery voltage is applied to terminals 1 and 2)

    If the result is not as specified, replace the relay.

Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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