John Deere 650H Speed Sensor Removal and Troubleshooting

[MikePhua]

Introduction
The John Deere 650H crawler dozer, introduced in the early 2000s, has become a staple in the construction industry due to its reliability and performance. A critical component of its drivetrain system is the speed sensor, which monitors the rotational speed of the tracks and communicates this data to the machine's electronic control module (ECM). This information is vital for functions like auto-tracking and anti-stall. However, issues with the speed sensor can lead to operational challenges.
Understanding the Speed Sensor's Role
The speed sensor on the 650H is responsible for detecting the speed of the tracks and relaying this information to the ECM. This data allows the machine to adjust its operations accordingly, ensuring optimal performance. A malfunctioning speed sensor can disrupt these processes, leading to symptoms such as mistracking or erratic movement.
Symptoms of a Faulty Speed Sensor

• Mistracking: The dozer may veer to one side, indicating uneven power distribution between the tracks.
  
• Erratic Movement: Unpredictable speed changes or stalling, especially under load.
  
• Diagnostic Trouble Codes (DTCs): Codes like F3M4 or F3M7, indicating issues with the left or right drive motor speed sensors, respectively.
  
• Loss of Auto-Tracking and Anti-Stall Features: Disabling the sensor can lead to the loss of these automated features.
  

Removing the Speed Sensor

1. Preparation:
   • Ensure the dozer is on a stable surface and the engine is turned off.
     
   • Disconnect the battery to prevent any electrical hazards.
     
2. Locating the Sensor:
   • The speed sensor is typically mounted on the drive motor assembly.
     
   • Refer to the machine's service manual for the exact location.
     
3. Disconnection:
   • Carefully disconnect the electrical connector from the sensor.
     
   • Take note of the connector's orientation for reinstallation.
     
4. Removal:
   • Using appropriate tools, remove any bolts or fasteners securing the sensor.
     
   • Gently pull the sensor out of its mounting position.
     
5. Inspection:
   • Examine the sensor for signs of wear, corrosion, or damage.
     
   • Check the electrical connector for any bent pins or corrosion.
     

Reinstalling the Speed Sensor

1. Preparation:
   • If replacing the sensor, ensure the new one matches the specifications of the original.
     
   • Apply a small amount of dielectric grease to the electrical connector to prevent corrosion.
     
2. Installation:
   • Insert the sensor into its mounting position.
     
   • Secure it with the appropriate bolts or fasteners.
     
3. Reconnection:
   • Reconnect the electrical connector, ensuring it is firmly in place.
     
4. Testing:
   • Reconnect the battery and start the engine.
     
   • Monitor the machine's performance to ensure the issue has been resolved.
     

Calibration and System Reset
After reinstalling the speed sensor, it may be necessary to calibrate the system to ensure accurate readings. This process can typically be done through the machine's diagnostic interface. Refer to the service manual for detailed calibration procedures.
Common Issues and Solutions

• Erratic Movement After Sensor Replacement:
  • Ensure the sensor is properly aligned and securely fastened.
    
  • Check for any wiring issues or loose connections.
    
• Persistent Fault Codes:
  • Clear any stored codes using the diagnostic tool.
    
  • If the codes return, further investigation into the wiring harness or ECM may be necessary.
    

Conclusion
The speed sensor is a vital component of the John Deere 650H crawler dozer's drivetrain system. Proper maintenance and timely replacement of a faulty sensor can prevent operational disruptions and ensure the machine performs at its best. Always refer to the machine's service manual for specific procedures and safety guidelines.