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Pinpoint Test C: DTC P0579 Or DTC P0581 - Cruise Control Switch Circuit Failure

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.
  1. C1 CHECK THE SPEED CONTROL SWITCH CIRCUITS FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: PCM C175b.
    • Key in ON position.
    • Turn the parking lamps on.
    • Measure the voltage between the PCM C175B-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 1: Checking The Speed Control Switch Circuits For A Short To Voltage
      G04584968Courtesy of FORD MOTOR CO.
    • Is any voltage present? 

    Yes  : TURN the parking lamps off. GO to C2.

    No  : TURN the parking lamps off. GO to  C5.

  2. C2 CHECK CIRCUITS 151 (LB/BK) AND 848 (DG/OG) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Clockspring C218a.
    • Key in ON position.
    • Turn the parking lamps on.
    • Measure the voltage between the PCM C175b-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 2: Checking Circuits 151 (LB/BK) And 848 (DG/OG) For A Short To Voltage
      G04584969Courtesy of FORD MOTOR CO.
    • Is any voltage present? 

    Yes  : REPAIR the circuit(s) in question. CLEAR the DTCs. REPEAT the self-test.

    No  : GO to C3.

  3. C3 CHECK THE CLOCKSPRING FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Connect: Clockspring C218a.
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
    • Connect the restraint system diagnostic tool to the upper clockspring.
    • Disconnect: Clockspring C218b.
      • WARNING: Make sure there is no one inside the vehicle and that there is nothing blocking or set in front of any air bag module when the battery is connected. Failure to follow these instructions may result in personal injury.
    • Connect the battery.
    • Key in ON position.
    • Turn the parking lamps on.
    • Measure the voltage between the PCM C175b-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 3: Checking The Clockspring For A Short To Voltage
      G04584970Courtesy of FORD MOTOR CO.
    • Is any voltage present? 

    Yes  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

    No  : GO to C4.

  4. C4 CHECK THE STEERING WHEEL HARNESS FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Connect: Clockspring C218b.
    • Disconnect: Speed Control Switch(es).
    • Key in ON position.
    • Turn the parking lamps on.
    • If equipped with remote audio/climate control switches, measure the voltage between the speed control switch C203, harness side and ground as follows:
      SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Speed Control Switch Circuit
      Pin 1 151 (LB/BK)
      Pin 2 848 (DG/OG)
    • If not equipped with remote audio/climate control switches, measure the voltage between the speed control switch C2330a, harness side and ground as follows:
      SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Speed Control Switch Circuit
      Pin 1 151 (LB/BK)
      Pin 2 133 (BK)
      Pin 3 848 (DG/OG)
    • Is any voltage present? 

    Yes  : REPAIR the circuit in question. DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

    No  : INSTALL a new speed control switch(es). REFER to SPEED CONTROL SWITCH . DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

  5. C5 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR A SHORT TO GROUND 
    • Key in OFF position.
    • Measure the resistance between the PCM C175b-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 4: Checking The Speed Control Switch Circuitry For A Short To Ground
      G04584971Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 

    Yes  : GO to  C9.

    No  : GO to C6.

  6. C6 CHECK THE CLOCKSPRING FOR A SHORT TO GROUND 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
    • Disconnect: Clockspring C218b.
    • Measure the resistance between the PCM C175b-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 5: Checking The Clockspring For A Short To Ground
      G04584972Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 

    Yes  : GO to  C8.

    No  : GO to C7.

  7. C7 CHECK CIRCUITS 151 (LB/BK) AND 848 (DG/OG) FOR A SHORT TO GROUND 
    • Disconnect: Clockspring C218a.
    • Measure the resistance between the PCM C175b-19, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and ground.
      Fig 6: Checking Circuits 151 (LB/BK) And 848 (DG/OG) For A Short To Ground
      G04584973Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 

    Yes  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

    No  : REPAIR the circuit(s) in question. CLEAR the DTCs. REPEAT the self-test.

  8. C8 CHECK THE SPEED CONTROL SWITCH FOR A SHORT TO GROUND 
    • Disconnect: Speed Control Switch(es).
    • If equipped with remote audio/climate control switches, measure the resistance between the speed control switch C203, harness side and ground as follows:
      SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Speed Control Switch Circuit
      Pin 1 151 (LB/BK)
      Pin 2 848 (DG/OG)
    • If not equipped with remote audio/climate control switches, measure the resistance between the speed control switch C2330a, harness side and ground as follows:
      SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Speed Control Switch Circuit
      Pin 1 151 (LB/BK)
      Pin 2 133 (BK)
      Pin 3 848 (DG/OG)
    • Are the resistances greater than 10,000 ohms? 

    Yes  : INSTALL a new speed control switch(es). REFER to SPEED CONTROL SWITCH . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

    No  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.

  9. C9 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR AN OPEN 
    • Measure the resistance between the PCM C175b-19, circuit 151 (LB/BK), harness side and the PCM C175b-30, circuit 848 (DG/OG), harness side.
      Fig 7: Measuring Resistance Between PCM C175b-19, Circuit 151 (LB/BK) And PCM C175b-30, Circuit 848 (DG/OG)
      G04584974Courtesy of FORD MOTOR CO.
    • Is the resistance between 3,965 and 4,655 ohms? 

    Yes  : GO to  C13.

    No  : GO to C10.

  10. C10 CHECK CIRCUITS 151 (LB/BK) AND 848 (DG/OG) FOR AN OPEN 
    • Disconnect: Clockspring C218a.
    • Measure the resistance between the PCM C175b-19, circuit 151 (LB/BK), harness side and the clockspring C218a-13, circuit 151 (LB/BK), harness side; and between the PCM C175b-30, circuit 848 (DG/OG), harness side and the clockspring C218a-3, circuit 848 (DG/OG), harness side.
      Fig 8: Checking Circuits 151 (LB/BK) And 848 (DG/OG) For An Open
      G04584975Courtesy of FORD MOTOR CO.
    • Are the resistances less than 5 ohms? 

    Yes  : GO to C11.

    No  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.

  11. C11 CHECK THE CLOCKSPRING 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
    • Disconnect: Clockspring C218b.
    • Measure the resistance between the clockspring C218b pin 11, component side and the clockspring C218a pin 3, component side; and between the clockspring C218b pin 3, component side and the clockspring C218a pin 13, component side.
      Fig 9: Checking Clockspring
      G04584976Courtesy of FORD MOTOR CO.
    • Are the resistances less than 5 ohms? 

    Yes  : GO to C12.

    No  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.

  12. C12 CHECK THE STEERING WHEEL HARNESS 
    • Disconnect: Speed Control Switch(es).
    • If equipped with remote audio/climate control switches, measure the resistance between the clockspring C218b, harness side and the speed control switch C203, harness side as follows:
      CLOCKSPRING AND SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Clockspring Connector-Pin Speed Control Switch Connector-Pin Circuit
      C218b-3 C203-1 151 (LB/BK)
      C218b-11 C203-2 848 (DG/OG)
    • If not equipped with remote audio/climate control switches, measure the resistance between the clockspring C218b, harness side and the speed control switch; and between the speed control switch C2330a, harness side and the speed control switch C2330b, harness side as follows:
      CLOCKSPRING AND SPEED CONTROL SWITCH PINS AND CIRCUITS REFERENCE

      Clockspring Connector-Pin Speed Control Switch Connector-Pin Speed Control Switch Connector-Pin Circuit
      C218b-3 C2330a-1 - 151 (LB/BK)
      C218b-3 - C2330b-6 151 (LB/BK)
      C218b-11 C2330a-3 - 848 (DG/OG)
      C218b-11 - C2330b-4 848 (DG/OG)
      - C2330a-2 C2330b-5 133 (BK)
    • Are the resistances less than 5 ohms? 

    Yes  : INSTALL new speed control switch(es). REFER to SPEED CONTROL SWITCH . CLEAR the DTCs. REPEAT the self-test.

    No  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.

  13. C13 CHECK FOR CORRECT PCM OPERATION 
    • Disconnect all the PCM connectors.
    • Check for:
      • corrosion
      • pushed-out pins
    • Connect all the PCM connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 

    Yes  : INSTALL a new PCM. REFER to ELECTRONIC ENGINE CONTROLS . TEST the system for normal operation.

    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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