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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 2007 Lincoln MKX and 2007 Ford Edge. 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.
      • Fig 1: Measuring Voltage Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023012Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • 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 VES10 (WH) AND RES08 (GN/BN) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Clockspring C218a
    • Key in ON position.
    • Turn the parking lamps on.
      • Fig 2: Measuring Voltage Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023012Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • 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
      • 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.
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
    • Disconnect: Upper Clockspring C218b
    • Connect the restraint system diagnostic tools (418-F395) to the upper clockspring air bag connector.
    • Connect the battery.
    • Key in ON position.
    • Turn the parking lamps on.
      • Fig 3: Measuring Voltage Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023012Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • Is any voltage present? 
    1. 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.
    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 . CLEAR the DTCs. REPEAT the self-test.
  4. C4 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR A SHORT TO GROUND 
    • Key in OFF position.
      • Fig 4: Measuring Resistance Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023013Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • 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 .
    • Disconnect: Upper Clockspring C218b
      • Fig 5: Measuring Resistance Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023013Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • 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 . CLEAR the DTCs. REPEAT the self-test.
    2. NO  : Go to  C6.
  6. C6 CHECK CIRCUITS VES10 (WH) AND RES08 (GN/BN) FOR A SHORT TO GROUND 
    • Disconnect: Clockspring C218a
      • Fig 6: Measuring Resistance Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023013Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-56, circuit VES10 (WH), harness side and ground; and between the PCM C175b-57, circuit RES08 (GN/BN), harness side and ground.
    • Are the resistances greater than 10,000 ohms? 
    1. 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.
    2. NO  : REPAIR the circuit in question. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.
  7. C7 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR AN OPEN 
      Fig 7: Measuring Resistance Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023014Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-56, circuit VES10 (WH), harness side and the PCM C175b-57, circuit RES08 (GN/BN), harness side.
    • Is the resistance between 4,279 and 4,363 ohms? 
    1. YES  : Go to  C10.
    2. NO  : Go to  C8.
  8. C8 CHECK CIRCUITS VES10 (GN/BK) AND RES08 (GN/BN) FOR AN OPEN 
    • Disconnect: Clockspring C218a
      • Fig 8: Measuring Resistance Between PCM C175B-56 & C175B-57, Circuit VES10 (WH) & RES08 (GN/BN)
      GF0023015Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-56, circuit VES10 (WH), harness side and the clockspring C218a-15, circuit VES10 (WH), harness side; and between the PCM C175b-57, RES08 (GN/BN), harness side and the clockspring C218a-14, circuit RES08 (GN/BN), harness side.
    • Are the resistances less than 5 ohms? 
    1. YES  : Go to  C9.
    2. NO  : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.
  9. C9 CHECK THE CLOCKSPRING 
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
      • Fig 9: Measuring Resistance Between Clockspring C218A Pin 15 C218B Pin 8, C218A Pin 14 & C218B Pin 9
      GF0023016Courtesy of FORD MOTOR CO.
    • Measure the resistance between the clockspring C218a pin 15, component side and the upper clockspring C218b pin 8, component side; and between the clockspring C218a pin 14, component side and the upper clockspring C218b pin 9, component side.
    • Are the resistances less than 5 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 . CLEAR the DTCs. REPEAT the self-test.
    2. 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.
  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 seat 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 . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . 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 module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.
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