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Pinpoint Test B: The Horn Is Always On

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

Refer to SYSTEM WIRING DIAGRAMS , Horn/Cigar Lighter for schematic and connector information.

Normal Operation 

The horn relay is controlled through circuit 1 (DB) by the horn switch and through the lighting control module (LCM). When the horn switch is pressed, the horn relay control circuit 1 (DB) is grounded through the clockspring to the vehicle harness. The horn relay is then energized causing voltage to be applied to circuit 6 (YE/LG), enabling the horn to sound.

When the LCM has enabled the anti-theft system, the LCM supplies a ground through the horn relay control circuit 1 (DB). The horn relay is then energized causing voltage to be applied to circuit 6 (YE/LG), enabling the horn to sound.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST B: THE HORN IS ALWAYS ON 

  1. B1 CHECK THE HORN CIRCUIT 
    • Key in OFF position.
    • Disconnect: Horn Relay
    • Does the horn continue to sound? 
    1. YES  : REPAIR circuit 6 (YE/LG). TEST the system for normal operation.
    2. NO  : Go to  B2.
  2. B2 CHECK THE HORN RELAY 
    • Substitute a known good relay.
    • Check the horn.
    • Dose the horn sound? 
    1. YES  : REMOVE the known good relay. INSTALL a new horn relay. TEST the system for normal operation.
    2. NO  : REMOVE the known good relay. Go to  B3.
  3. B3 CHECK THE LCM 
    • Disconnect: LCM C2145b
    • Does the horn continue to sound? 
    1. YES  : Go to  B4.
    2. NO  : Go to  B7.
  4. B4 CHECK CIRCUIT 1 (DB) FOR A SHORT TO GROUND 
    • Disconnect: Clockspring C218a
    • Does the horn continue to sound? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : Go to  B5.
  5. B5 CHECK THE CLOCKSPRING 
    • Connect: Clockspring C218a
    • Remove the driver air bag module. Refer to REMOVAL AND INSTALLATION article.
    • Disconnect: Clockspring C218b
    • Does the horn continue to sound? 
    1. YES  : INSTALL a new clockspring. REFER to REMOVAL AND INSTALLATION article. TEST the system for normal operation.
    2. NO  : Go to  B6.
  6. B6 CHECK THE STEERING WHEEL SWITCH HARNESS 
    • Visually inspect the steering wheel switch harness for shorts or damage.
    • Is the steering wheel switch harness OK? 
    1. YES  : INSTALL a new driver air bag module, or a new steering wheel, as necessary. REFER to REMOVAL AND INSTALLATION article for the driver air bag module, or REMOVAL & INSTALLATION article for the steering wheel. TEST the system for normal operation.
    2. NO  : INSTALL a new steering wheel switch harness. INSTALL the driver air bag module. REFER to REMOVAL AND INSTALLATION article. TEST the system for normal operation.
  7. B7 CHECK THE LCM FOR CORRECT OPERATION 
    • Disconnect all the LCM connectors.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect all the LCM connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    1. YES  : INSTALL a new LCM. REFER to REMOVAL AND INSTALLATION article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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