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

Refer to appropriate SYSTEM WIRING DIAGRAMS - EDGE or SYSTEM WIRING DIAGRAMS - MKX article, Speed Control for schematic and connector information.

Normal Operation 

The PCM sends a signal through circuit VES10 (WH) to the speed control switches, which passes through the clockspring. The return signal is sent to the PCM through circuit RES08 (GN/BN) and the clockspring.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST C: DTC P0579 OR DTC P0581 - SPEED CONTROL SWITCH CIRCUIT FAILURE 

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
      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
      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 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.
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM article.
    • 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
      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 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.
      • Fig 4: Measuring Resistance
      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 article.
    • Disconnect: Upper Clockspring C218b
      • Fig 5: Measuring Resistance
      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 article. 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
      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 article. 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 
      Fig 7: Measuring Resistance
      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
      GF0044350Courtesy 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.
      • Fig 9: Measuring Resistance
      GF0044351Courtesy of FORD MOTOR CO.
    • Measure the resistance 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 article.
      • Fig 10: Measuring Resistance
      GF0044352Courtesy of FORD MOTOR CO.
    • Measure the resistance between the clockspring C218a pin 15, component side and the upper clockspring C218b pin 8, component side.
      • Fig 11: Measuring Resistance
      GF0044353Courtesy of FORD MOTOR CO.
    • Measure the resistance 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 article. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : INSTALL a new clockspring. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. 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 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 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 module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM article. CLEAR the DTCs. REPEAT the self-test.
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