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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 2009 Ford Mustang. 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 Connector And Ground
      G03883128Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), 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 248 (TN/OG) AND 133 (BK) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Clockspring C2274
    • Key in ON position.
    • Turn the parking lamps on.
      • Fig 2: Checking Circuits 248 (TN/OG) & 133 (BK) For A Short To Voltage
      G03883128Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), 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 C2274
    • Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM article.
    • Connect the restraint system diagnostic tools (418-F395) to the upper clockspring air bag connector.
    • Disconnect: Upper Clockspring
      • 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.
      • Fig 3: Measuring Voltage Between PCM C175B-19, Circuit 248 (TN/OG), Harness Side & Ground
      G03883128Courtesy of FORD MOTOR CO.
    • Measure the voltage between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), 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 Between PCM C175B-19, Circuit 248 (TN/OG), Harness Side & Ground
      G03883131Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), 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
      • Fig 5: Measuring Resistance Between PCM C175B-19, Circuit 248 (TN/OG), Harness Side & Ground
      G03883131Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), 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 . DISCONNECT the battery. 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 248 (TN/OG) AND 133 (BK) FOR A SHORT TO GROUND 
    • Disconnect: Clockspring C2274
      • Fig 6: Measuring Resistance Between PCM C175B-19, Circuit 248 (TN/OG), Harness Side & Ground
      G03883131Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-19, circuit 248 (TN/OG), harness side and ground; and between the PCM C175b-30, circuit 133 (BK), harness side and ground.
    • 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 
    • Measure the resistance between the PCM C175b-19, circuit 248 (TN/OG), harness side and the PCM C175b-30, circuit 133 (BK), harness side.
    • Is the resistance between 4,100 and 4,500 ohms? 
    1. YES  : Go to  C10.
    2. NO  : Go to  C8.
  8. C8 CHECK CIRCUITS 248 (TN/OG) AND 133 (BK) FOR AN OPEN 
    • Disconnect: Clockspring C2274
      • Fig 7: Measuring Resistance Between PCM C175B-19, Circuit 248 (TN/OG), Harness Side
      GF0001255Courtesy of FORD MOTOR CO.
    • Measure the resistance between the PCM C175b-19, circuit 248 (TN/OG), harness side and the clockspring C2274-4, circuit 248 (TN/OG), harness side; and between the PCM C175b-30, circuit 133 (BK), harness side and the clockspring C2274-5, circuit 133 (BK), 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.
    • Disconnect: Upper Clockspring
      • Fig 8: Measuring Resistance Between Clockspring C2274 Pin 4, 5 & Upper Clockspring Connector Pin 2, 3
      GF0015964Courtesy of FORD MOTOR CO.
    • Measure the resistance between the clockspring C2274 pin 4, component side and the upper clockspring connector pin 2, component side; and between the clockspring C2274 pin 5, component side and the upper clockspring connector pin 3, component side.
    • Are the resistances less than 5 ohms? 
    1. YES  : 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.
    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.
  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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