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Home >> Mercury >> 2008 >> Milan Base, 3.0 1, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 107 (Horn System -- F250-F550 Super Duty) >> Diagnosis And Testing >> Horn >> Pinpoint Tests >> Pinpoint Test A: The Horn Does Not Sound

Pinpoint Test A: The Horn Does Not Sound

WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
  1. A1 RETRIEVE THE DIAGNOSTIC TROUBLE CODES (DTCs) 
    • Key in ON position.
    • Record the results from the vehicle security module self-test.
    • Are any DTCs recorded? 
  2. A2 CHECK THE INOPERATIVE HORN FUNCTION 
    • Press the horn switch.
    • Does the horn sound? 
    • Yes  : GO to A3.
    • No  : GO to  A7.
  3. A3 CHECK THE VEHICLE SECURITY MODULE OUTPUT 
    • Trigger the vehicle security module active command HORN OUTPUT ON on the diagnostic tool.
    • Does the horn sound? 
    • Yes  : GO to  A14.
    • No  : GO to A4.
  4. A4 CHECK CIRCUIT 1 (DB) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Vehicle Security Module C2113b.
    • Disconnect: Central Junction Box (CJB) C270a.
    • Key in ON position.
    • Measure the voltage between the vehicle security module C2113b pin 6, circuit 1 (DB), harness side and ground.
      Fig 1: Checking Circuit 1 (DB) For Short To Voltage
      G03910751Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    • Yes  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
    • No  : GO to A5.
  5. A5 CHECK CIRCUIT 1 (DB) FOR AN OPEN TO THE VEHICLE SECURITY MODULE 
    • Key in OFF position.
    • Measure the resistance between the vehicle security module C2113b pin 6, circuit 1 (DB), harness side and the CJB C270a pin 19, circuit 1 (DB), harness side.
      Fig 2: Checking Circuit 1 (DB) For Open To Vehicle Security Module
      G03910752Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to A6.
    • No  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
  6. A6 CHECK THE CJB FOR AN OPEN 
    • Connect: CJB C270a.
    • Connect a fused (15A) jumper wire between the vehicle security module C2113b pin 6, harness side and ground.
      Fig 3: Checking CJB For Open
      G03910753Courtesy of FORD MOTOR CO.
    • Does the horn sound? 
    • Yes  : GO to  A14.
    • No  : REPAIR or INSTALL a new CJB. CLEAR the DTCs. REPEAT the self-test.
  7. A7 CHECK CIRCUIT 57 (BK) FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: Horn C131.
    • Measure the resistance between the horn C131 pin 1, circuit 57 (BK), harness side and ground.
      Fig 4: Checking Circuit 57 (BK) For Open
      G03924769Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to A8.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  8. A8 CHECK THE VOLTAGE TO THE HORN 
    • Measure the voltage between the horn C131 pin 2, circuit 6 (YE/LG), harness side and the horn C131 pin 1, circuit 57 (BK), harness side, while pressing the horn switch.
      Fig 5: Checking Voltage To Horn
      G03924770Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    • Yes  : INSTALL a new horn. REFER to HORN . TEST the system for normal operation.
    • No  : GO to A9.
  9. A9 CHECK CIRCUIT 6 (YE/LG) FOR AN OPEN 
    • Disconnect: Central Junction Box (CJB) C270h.
    • Measure the resistance between the CJB C270h pin 9, circuit 6 (YE/LG), harness side and the horn C131 pin 2, circuit 6 (YE/LG), harness side.
      Fig 6: Checking Circuit 6 (YE/LG) For Open
      G03924771Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to A10.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  10. A10 CHECK THE HORN SWITCH CIRCUITRY 
    • Disconnect: CJB C270a.
    • Measure the resistance between the CJB C270a pin 19, circuit 1 (DB), harness side and ground, while pressing and releasing the horn switch.
      Fig 7: Checking Horn Switch Circuitry
      G03910757Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms with the horn switch pressed, and greater than 10,000 ohms with the horn switch released? 
    • Yes  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
    • No  : GO to A11.
  11. A11 CHECK CIRCUIT 1 (DB) FOR AN OPEN 
    • Disconnect: Clockspring C218a.
    • Measure the resistance between the CJB C270a pin 19, circuit 1 (DB), harness side and the clockspring C218a pin 4, circuit 1 (DB), harness side.
      Fig 8: Checking Circuit 1 (DB) For Open
      G03910758Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to A12.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  12. A12 CHECK CIRCUIT 57 (BK) FOR GROUND 
    • For Mexico vehicles, measure the resistance between the clockspring C218a pin 6, circuit 57 (BK), harness side and ground.
      Fig 9: Measuring Resistance Between Clockspring C218A Pin 6, Circuit 57 (BK), Harness Side And Ground (For Mexico Vehicles)
      G03910759Courtesy of FORD MOTOR CO.
    • For all other vehicles, measure the resistance between the clockspring C218a pin 7, circuit 57 (BK), harness side and ground.
      Fig 10: Measuring Resistance Between Clockspring C218A Pin 7, Circuit 57 (BK), Harness Side And Ground (For All Other Vehicles)
      G03924775Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to A13.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  13. A13 CHECK THE HORN SWITCH CIRCUITRY 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
    • Measure the resistance between the horn pad switch connector pins under the following conditions:
      HORN SWITCH CONTINUITY

      Steering Wheel Pad Horn Switch Position Resistance
      Pressed Less than 5 ohms
      Released Greater than 10,000 ohms
      Fig 11: Checking Horn Switch Circuitry
      G03910760Courtesy of FORD MOTOR CO.
    • Are the resistances correct? 
  14. A14 CHECK FOR CORRECT VEHICLE SECURITY MODULE OPERATION 
    • Disconnect all the vehicle security module connectors.
    • Check for:
      • corrosion
      • pushed-out pins
    • Connect any disconnected connectors making sure they are seated correctly.
    • Make sure all other system connectors are fully seated.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    • Yes  : INSTALL a new vehicle security module. REFER to MULTIFUNCTION ELECTRONIC MODULES . CLEAR the DTCs. REPEAT the self-test.
    • No  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.
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