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

WARNING: This page is about a different car, the 2005 Mercury Montego, 2005 Ford Freestyle, and 2005 Ford Five Hundred. However, it is still accessible from the selected car via links, so may be relevant.

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-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 1: Measuring Voltage Between PCM Connector And Ground
  Courtesy 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 C4.
C2 CHECK CIRCUITS 151 (LB/BK) AND 848 (DG/OG) FOR A SHORT TO VOLTAGE
- Key in OFF position.
- Disconnect: Clockspring C2274a.
- Key in ON position.
- Turn the parking lamps on.
- Measure the voltage between the PCM C175b-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 2: Measuring Voltage Between PCM Connector And Ground
  Courtesy of FORD MOTOR CO.
- Is any voltage present?
- Yes : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.
- No : TURN the parking lamps off. GO to C3.
C3 CHECK THE CLOCKSPRING FOR A SHORT TO VOLTAGE
- Key in OFF position.
- Connect: Clockspring C2274a.
- Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
- Connect the restraint system diagnostic tool (418-F403) to the upper clockspring air bag connector.
- Disconnect: Upper Clockspring.
- Connect the battery.
- Key in ON position.
- Turn the parking lamps on.
- Measure the voltage between the PCM C175b-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 3: Measuring Voltage Between PCM Connector And Ground
  Courtesy 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 : 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.
C4 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR A SHORT TO GROUND
- Key in OFF position.
- Measure the resistance between the PCM C175b-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 4: Measuring Resistance Between PCM Connector And Ground
  Courtesy of FORD MOTOR CO.
- Are the resistances greater than 10,000 ohms?
- Yes : GO to C7.
- No : GO to C5.
C5 CHECK THE CLOCKSPRING FOR A SHORT TO GROUND
- Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
- Disconnect: Upper Clockspring.
- Measure the resistance between the PCM C175b-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 5: Measuring Resistance Between PCM Connector And Ground
  Courtesy of FORD MOTOR CO.
- Are the resistances greater than 10,000 ohms?
- 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.
- No : GO to C6.
C6 CHECK CIRCUITS 151 (LB/BK) AND 848 (DG/OG) FOR A SHORT TO GROUND
- Disconnect: Clockspring C2274a.
- Measure the resistance between the PCM C175b-30, circuit 151 (LB/BK), harness side and ground; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and ground.
  
  Fig 6: Measuring Resistance Between PCM Connector And Ground
  Courtesy 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 in question. INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.
C7 CHECK THE SPEED CONTROL SWITCH CIRCUITRY FOR AN OPEN
- Disconnect: Clockspring C2274a.
- Measure the resistance between the PCM C175b-30, circuit 151 (LB/BK), harness side and the clockspring C2274a-5, circuit 151 (LB/BK), harness side; and between the PCM C175b-19, circuit 848 (DG/OG), harness side and the clockspring C2274a-4, circuit 848 (DG/OG), harness side.
  
  Fig 7: Checking Speed Control Switch Circuitry For An Open
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : GO to C8.
- No : REPAIR the circuit in question. CLEAR the DTCs. REPEAT the self-test.
C8 CHECK THE CLOCKSPRING
- Remove the driver air bag module. Refer to SUPPLEMENTAL RESTRAINT SYSTEM .
- Disconnect: Upper Clockspring.
- Measure the resistance between the upper clockspring pin 3, component side and the clockspring pin 5, component side; and between the upper clockspring pin 2, component side and the clockspring pin 4, component side.
  
  Fig 8: Checking Clockspring
  Courtesy of FORD MOTOR CO.
- Are the resistances less than 5 ohms?
- Yes : GO to C9.
- 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.
C9 CHECK THE SPEED CONTROL SWITCH
- Measure the resistance between the upper clockspring pin 2, harness side and the upper clockspring pin 3, harness side.
  
  Fig 9: Checking Speed Control Switch
  Courtesy of FORD MOTOR CO.
- Is the resistance between 3,965 and 4,655 ohms?
- Yes : GO to C10.
- No : INSTALL 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.
C10 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 are seated 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 . INSTALL the driver air bag module. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . 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. INSTALL the driver air bag. REFER to SUPPLEMENTAL RESTRAINT SYSTEM . CLEAR the DTCs. REPEAT the self-test.