Troubleshooting Power Loss After Temperature Sensor Replacement on a Bobcat 743

[MikePhua]

The Bobcat 743, a popular skid steer loader, is known for its durability and versatility in various construction, landscaping, and agricultural tasks. However, like any heavy equipment, issues can arise over time that affect its performance. One such issue is power loss following the replacement of the temperature sensor. In this article, we’ll discuss the possible causes and solutions for a Bobcat 743 that loses power after a temperature sensor replacement, providing insights into troubleshooting and repair.
Understanding the Role of the Temperature Sensor
Before diving into troubleshooting, it’s essential to understand the function of the temperature sensor in the Bobcat 743. The temperature sensor monitors the engine coolant temperature and sends signals to the machine’s electrical system. This data is used by the engine control module (ECM) to regulate various engine functions, including fuel injection and the cooling fan.
When the sensor detects high temperatures, it triggers the activation of cooling mechanisms or alerts the operator to potential overheating. Conversely, if the sensor is faulty or incorrectly installed, it can lead to improper readings that may cause power loss, erratic engine behavior, or engine shutdowns.
Common Issues After Replacing the Temperature Sensor
Several problems can arise after replacing the temperature sensor in a Bobcat 743, leading to a loss of power. These issues often relate to electrical connections, sensor calibration, or wiring problems.

1. Incorrect Wiring or Loose Connections
   One of the most common reasons for power loss after replacing the temperature sensor is a loose or incorrect wiring connection. If the sensor’s wiring is not properly reconnected to the ECM or if the terminals are not securely fastened, it can cause an interruption in the signal sent to the engine control system, resulting in loss of power.
   Solution: Double-check the wiring connections and ensure that all connectors are secure. Look for any signs of fraying, corrosion, or loose terminals that could be causing a poor connection. If necessary, use a multimeter to test for continuity in the wiring.
   
2. Faulty Sensor Installation
   Another issue could be the improper installation of the temperature sensor itself. If the sensor is not correctly seated or tightened, it can lead to inaccurate temperature readings or even cause the sensor to malfunction. Additionally, using a non-compatible sensor could lead to incompatibility with the Bobcat 743’s ECM.
   Solution: Verify that the temperature sensor is correctly installed according to the manufacturer’s specifications. Ensure that the sensor is properly threaded into the block or housing and that it is seated tightly without overtightening. Always use OEM (Original Equipment Manufacturer) parts for replacements to avoid compatibility issues.
   
3. ECM Failure to Recognize New Sensor
   The ECM in a Bobcat 743 is programmed to recognize specific sensors and their respective readings. After replacing the temperature sensor, the ECM may fail to recognize the new sensor if it is not properly calibrated or if the ECM is not reset after the installation.
   Solution: Reset the ECM to ensure it recognizes the new sensor. This can typically be done by disconnecting the battery for a few minutes, which resets the ECM’s memory. If the issue persists, the ECM may need to be reprogrammed by a certified technician.
   
4. Blown Fuse or Electrical Short
   Replacing the temperature sensor may inadvertently cause an electrical short or a blown fuse. If the circuit is damaged during installation, it could result in a loss of power to other components, including the engine.
   Solution: Check all fuses related to the engine management system, as well as any relays that might be connected to the temperature sensor. Replace any blown fuses and test the system again. Inspect the wiring harness for any signs of short circuits or damaged insulation.
   
5. Air in the Cooling System
   After replacing the temperature sensor, if the cooling system has been disturbed (e.g., coolant lines were removed or altered), it is possible that air has entered the cooling system. Air pockets can cause inaccurate readings or prevent the sensor from properly monitoring the coolant temperature.
   Solution: Bleed the cooling system to remove any trapped air. This process involves opening the radiator cap and allowing coolant to flow until all air is purged. Follow the manufacturer’s instructions for the bleeding procedure to ensure the system is free of air.
   

Steps for Effective Troubleshooting
If your Bobcat 743 is experiencing power loss after a temperature sensor replacement, follow these troubleshooting steps to pinpoint the issue:

1. Inspect the Wiring and Connectors
   • Begin by visually inspecting the wiring connected to the new temperature sensor. Look for any signs of wear, corrosion, or loose connections.
     
   • Use a multimeter to test for continuity and verify that power is reaching the sensor.
     
2. Verify the Sensor Installation
   • Check the sensor for proper installation. Ensure it is tightly installed, using the correct tools and torque specifications.
     
   • Ensure that the sensor is compatible with your Bobcat 743 model. Using a non-OEM sensor may result in compatibility issues.
     
3. Reset the ECM
   • If the ECM has not recognized the new sensor, reset it by disconnecting the battery. This will force the ECM to relearn and adapt to the new sensor’s input.
     
   • After reconnecting the battery, check for any improvement in performance.
     
4. Check Fuses and Relays
   • Inspect the fuses and relays associated with the temperature sensor circuit and engine management. Replace any blown fuses, and ensure that all relays are functioning properly.
     
   • If necessary, consult the Bobcat 743 service manual for fuse location and specifications.
     
5. Check for Air in the Cooling System
   • If the cooling system was disturbed during the sensor replacement, air may have entered the system. Bleed the system to remove any trapped air that could affect sensor performance.
     
6. Test the System
   • After addressing the wiring, installation, and ECM issues, perform a thorough test of the system. Start the engine and let it warm up, ensuring that the temperature sensor is providing accurate readings and the engine is running smoothly.
     

Preventive Maintenance Tips for the Bobcat 743
To avoid issues like power loss or sensor failure in the future, regular maintenance is crucial:

• Regularly Inspect Wiring and Connectors: Check the wiring harness for any signs of wear, corrosion, or loose connections, especially if you’ve had previous electrical issues.
  
• Use OEM Parts: Always use genuine John Deere or Bobcat parts when replacing sensors and components. This ensures compatibility and longevity.
  
• Monitor the Cooling System: Keep an eye on coolant levels and ensure the system is free from leaks. Overheating can cause premature sensor failure and engine damage.
  
• Schedule Regular Service Intervals: Follow the recommended service intervals for fluid changes, filter replacements, and system checks to keep the Bobcat 743 in top working condition.
  

Conclusion
Power loss after a temperature sensor replacement on a Bobcat 743 can stem from several potential causes, including wiring issues, faulty sensor installation, or ECM recognition problems. By following a systematic troubleshooting process and addressing each of these factors, operators can restore proper function to their skid steer. Additionally, regular preventive maintenance can help avoid future issues and ensure the machine continues to perform reliably in demanding work environments.