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Pinpoint Test B: The Set Speed Fluctuates

WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. 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. B1 CHECK THE SPEED CONTROL CABLE/THROTTLE BODY LINKAGE 
    • Key in OFF position.
    • Visually inspect the speed control cable connections, the throttle body linkage, and the speed control actuator pulley cover.
    • Are the speed control cable connections, the throttle body linkage, and the speed control actuator pulley cover OK?  
    1. YES  : Go to  B2.
    2. NO  : INSTALL a new speed control cable or REPAIR the throttle body linkage. To INSTALL a new speed control cable, REFER to Speed Control Cable . TEST the system for normal operation. For repair of the throttle body linkage, REFER to ACCELERATION CONTROL article. TEST the system for normal operation. For repair of the speed control actuator pulley cover, INSTALL the cover correctly. TEST the system for normal operation.
  2. B2 CHECK THE SPEEDOMETER OPERATION 
    • Drive the vehicle and observe the speedometer operation.
    • Does the speedometer needle fluctuate? 
    1. YES  : REFER to INSTRUMENT CLUSTER article.
    2. NO  : Go to  B3.
  3. B3 CHECK FOR A BASE ENGINE CONCERN 
    • Drive the vehicle and determine if there is a base engine concern.
    • Is a base engine concern present? 
    1. YES  : REFER to the Introduction - Gasoline Engines article.
    2. NO  : Go to  B4.
  4. B4 CHECK THE VEHICLE SPEED SIGNAL VOLTAGE 
    CAUTION: Make sure the vehicle is secured correctly before attempting to place the transmission range selector lever in DRIVE (D) or in 1st gear if equipped with a manual transaxle.
    • Disconnect: Speed Control Actuator C122
    • Disconnect: Active Torque Coupling C3254 (if equipped)
    • Raise the vehicle on a hoist. REFER to JACKING AND LIFTING article.
      • NOTE: For vehicles with a manual transaxle, place the transaxle into 1st gear.
    • Start the vehicle, place the transaxle in DRIVE (D) and with the engine at idle allow all of the drive wheels to spin.
      • Fig 1: Checking Vehicle Speed Signal Voltage
      GF0010779Courtesy of FORD MOTOR CO.
    • Measure and record the AC voltage between the speed control actuator C122-3, circuit 679 (GY/BK), harness side and ground with the vehicle drive wheels spinning a minimum of 8 km/h (5 mph).
    • Apply the brakes until the drive wheels come to a stop. Place the transaxle in PARK (P), fully engage the parking brake and turn the engine off.
    • Is the AC voltage greater than 4.5 volts? 
    1. YES  : Go to  B5.
    2. NO  : Go to  B6.
  5. B5 CHECK THE VEHICLE SPEED SIGNAL FREQUENCY 
    CAUTION: Make sure the vehicle is secured correctly before attempting to place the transmission range selector lever in DRIVE (D) or in 1st gear if equipped with a manual transaxle.
      NOTE: For vehicles with a manual transaxle, place the transaxle into 1st gear.
    • Start the vehicle, place the transaxle in DRIVE (D) and with the engine at idle allow all of the drive wheels to spin.
      • Fig 2: Checking Vehicle Speed Signal Frequency
      GF0025547Courtesy of FORD MOTOR CO.
    • Measure and record the frequency between the speed control actuator C122-3, circuit 679 (GY/BK), harness side and ground with the vehicle drive wheels spinning a minimum of 8 km/h (5 mph). Record the speedometer reading.
    • Apply the brakes until the drive wheels come to a stop. Place the transaxle in PARK (P), fully engage the parking brake and turn the engine off.
    • Divide the frequency reading by 2.2 to get a mph result and compare this to the reading of the speedometer (example: 10 mph = 22 Hz).
    • Does the frequency reading result match the speedometer reading? 
    1. YES  : INSTALL a new speed control actuator. REFER to Speed Control Actuator . TEST the system for normal operation.
    2. NO  : Go to  B6.
  6. B6 CHECK FOR CORRECT ABS MODULE OPERATION 
    • Disconnect the ABS module connector.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect the ABS module connector and make sure it seats correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still presents? 
    1. YES  : INSTALL a new ABS module. REFER to VEHICLE DYNAMIC SYSTEMS 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.
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