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

WARNING: This page is about a different car, the 2008 Mercury Sable, 2008 Ford Taurus X, and 2008 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  1. C1 CHECK THE SPEED CONTROL SWITCH CIRCUITRY 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-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 1: Measuring Voltage
      GF0023012Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
    1. YES  : TURN the parking lamps off. Go to  C2 .
    2. NO  : TURN the parking lamps off. Go to  C4 .
  2. C2 CHECK CIRCUITS RES08 (GN/BN) AND VES10 (WH) 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-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 2: Measuring Voltage
      GF0023012Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
    1. YES  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : TURN the parking lamps off. 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 article.
    • Connect the restraint system diagnostic tool (418-F395) to the upper clockspring air bag connector.
    • Disconnect: Upper Clockspring Connector
      • WARNING: Make sure no one is in the vehicle and there is nothing blocking or placed in front of any air bag module when the battery is connected. Failure to follow these instructions may result in serious personal injury in the event of an accidental deployment.
    • Connect the battery.
    • Key in ON position.
    • Turn the parking lamps on.
    • Measure the voltage between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 3: Measuring Voltage
      GF0023012Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
    1. YES  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : INSTALL a new speed control switch. REFER to Speed Control Switch . DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
  4. C4 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR A SHORT TO GROUND 
    • Key in OFF position.
    • Measure the resistance between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 4: Measuring Resistance
      GF0023013Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 
    1. YES  : Go to  C7.
    2. NO  : Go to  C5.
  5. C5 CHECK THE CLOCKSPRING FOR A SHORT TO GROUND 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM article.
    • Disconnect: Upper Clockspring
    • Measure the resistance between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 5: Measuring Resistance
      GF0023013Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 
    1. YES  : INSTALL a new speed control switch. REFER to Speed Control Switch . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : Go to  C6.
  6. C6 CHECK CIRCUITS RES08 (GN/BN) AND VES10 (WH) FOR A SHORT TO GROUND 
    • Disconnect: Clockspring C218a
    • Measure the resistance between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground; and between the PCM C175b-56, circuit VES10 (WH), harness side and ground.
      • Fig 6: Measuring Resistance
      GF0023013Courtesy of FORD MOTOR CO.
    • Are the resistances greater than 10,000 ohms? 
    1. YES  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : REPAIR the circuit in question. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
  7. C7 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR AN OPEN 
    • Disconnect: Clockspring C218a
    • Measure the resistance between the PCM C175b-57, circuit RES08 (GN/BN), harness side and the clockspring C218a-14, circuit RES08 (GN/BN), harness side; and between the PCM C175b-56, circuit VES10 (WH), harness side and the clockspring C218a-15, circuit VES10 (WH), harness side.
      • Fig 7: Measuring Resistance
      GF0023015Courtesy of FORD MOTOR CO.
    • Are the resistances less than 5 ohms? 
    1. YES  : Go to  C8.
    2. NO  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.
  8. C8 CHECK THE CLOCKSPRING 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM article.
    • Disconnect: Upper Clockspring
    • Measure the resistance between the clockspring C218a-14, component side and the upper clockspring pin 8, component side; and between the clockspring C218a-15, component side and the upper clockspring pin 9, component side.
      • Fig 8: Measuring Resistance
      GF0023016Courtesy of FORD MOTOR CO.
    • Are the resistances less than 5 ohms? 
    1. YES  : Go to  C9.
    2. NO  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
  9. C9 CHECK THE SPEED CONTROL SWITCH 
    • Measure the resistance between the upper clockspring pin 8, harness side and the upper clockspring pin 9, harness side.
      • Fig 9: Measuring Resistance
      GF0042491Courtesy of FORD MOTOR CO.
    • Is the resistance between 3,965 and 4,655 ohms? 
    1. YES  : Go to  C10.
    2. NO  : INSTALL new speed control switch. REFER to Speed Control Switch . DISCONNECT the battery. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
  10. C10 CHECK FOR CORRECT PCM OPERATION 
    • Disconnect all the PCM connectors.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect all the PCM connectors and make sure they are seated correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    1. YES  : INSTALL a new PCM. REFER to ELECTRONIC ENGINE CONTROLS article. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM 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. INSTALL the driver air bag. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
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