John Deere 690E LC: Issues with Running in Only L Mode

[MikePhua]

The John Deere 690E LC is a popular hydraulic excavator used in various construction and earth-moving applications. However, some users have reported an issue where the machine only runs correctly in Low (L) mode, with improper performance in other modes. This article examines the potential causes of this issue and provides guidance on troubleshooting and resolving the problem.
Understanding the Problem
The John Deere 690E LC is equipped with different operating modes, including High (H), Low (L), and sometimes a Power mode, which adjust the machine's performance based on the task. When the excavator is only functioning properly in Low mode but struggles in other modes, it can indicate a deeper issue in the hydraulic or control systems.
Operators have described issues such as:

• Sluggish or Unresponsive Performance: The excavator runs well in Low mode but becomes sluggish or unresponsive in High mode or Power mode.
  
• Loss of Power or Hydraulic Functionality: There is a noticeable reduction in digging, lifting, or digging force when the machine switches to a higher mode.
  
• Erratic Engine Behavior: In some cases, the engine may not accelerate properly or stalls when the mode is switched from Low to High or Power.
  

Possible Causes of the Issue
Several factors can contribute to this issue, including problems with the hydraulic system, transmission, or control systems.

1. Hydraulic System Problems:
   The hydraulic system is essential for the operation of various functions on the 690E LC, such as digging and lifting. If the hydraulic system is malfunctioning, it can cause the machine to perform poorly in higher power modes.
   • Hydraulic Pressure Issues: Low hydraulic pressure can cause poor machine performance, especially under load. A malfunctioning hydraulic pump, pressure relief valve, or fluid contamination can affect pressure levels.
     
   • Clogged Hydraulic Filters: Clogged filters restrict fluid flow and can reduce the machine's performance, particularly in higher modes that require increased hydraulic capacity.
     
2. Transmission or Gearbox Issues:
   Transmission problems can affect the machine’s ability to shift between modes properly. In cases where the machine only works in Low mode, a fault in the transmission might be limiting the performance in High or Power modes.
   • Transmission Fluid Levels: Low or dirty transmission fluid can cause shifting problems and improper power distribution. This can result in reduced performance when switching to higher modes.
     
   • Faulty Transmission Solenoids: The transmission solenoids control the shifting process, and if one is malfunctioning, it could prevent the machine from operating correctly in higher modes.
     
3. Engine Performance:
   The engine plays a crucial role in providing the necessary power for the hydraulic system and other components. A weak or inefficient engine can lead to performance issues in higher modes.
   • Fuel System Issues: Dirty fuel injectors or clogged filters can cause poor engine performance, especially at higher RPMs when more power is needed.
     
   • Engine Sensors and ECU Problems: Malfunctions in the engine control unit (ECU) or sensors can lead to incorrect fuel delivery, which could result in inadequate engine power when switching to higher modes.
     
4. Control System Malfunctions:
   The 690E LC is equipped with advanced electronic control systems that regulate the machine’s performance in different modes. A malfunction in these systems can lead to inconsistent or poor performance in High or Power mode.
   • Faulty Mode Selector Switch: If the mode selector switch is malfunctioning, it may not be sending the correct signals to the ECU, causing the machine to stay in Low mode or operate incorrectly in higher modes.
     
   • ECU Malfunction: The ECU monitors and controls several functions, including engine performance, hydraulic systems, and transmission. A faulty ECU could prevent the machine from operating efficiently in higher modes.
     

Troubleshooting and Solutions
Here are some steps you can take to diagnose and potentially resolve the issue with the John Deere 690E LC:

1. Check Hydraulic Fluid and Filters:
   Start by checking the hydraulic fluid levels and inspecting the filters for signs of clogging or contamination. Replacing clogged filters and topping off hydraulic fluid may improve performance. Also, inspect the hydraulic pump for any signs of wear or damage.
   
2. Inspect Transmission Fluid:
   Low or dirty transmission fluid could cause the machine to perform poorly in higher modes. Check the transmission fluid levels and ensure it’s clean. If necessary, replace the fluid and inspect the transmission for any faults, such as worn gears or solenoids.
   
3. Examine the Engine:
   Inspect the fuel system for clogged injectors or dirty filters. Ensure that the engine is receiving proper fuel flow. Check for any error codes in the ECU that could indicate issues with the engine sensors or fuel system.
   
4. Test the Mode Selector and ECU:
   Verify that the mode selector switch is functioning properly and that the signals are being correctly sent to the ECU. If the switch is faulty, it may need to be replaced. Additionally, consider having the ECU scanned for error codes that could pinpoint malfunctions in the control systems.
   
5. Consult with a Professional Technician:
   If you are unable to resolve the issue through basic checks and repairs, it may be necessary to consult with a professional technician who can run diagnostic tests on the hydraulic, transmission, and control systems. They will have the necessary tools and expertise to identify and fix complex issues.
   

Conclusion
When the John Deere 690E LC excavator only runs correctly in Low mode, it’s often a sign of underlying issues with the hydraulic system, transmission, or control systems. By performing a thorough inspection of key components such as the hydraulic fluid, transmission, engine, and electronic controls, you can diagnose and potentially resolve the issue. Regular maintenance and timely repairs are essential to keep the excavator running smoothly in all operating modes, ensuring reliable performance for various tasks.