Troubleshooting the GTH 644 No Drive Unless a Function is Called For

[MikePhua]

Introduction
The GTH 644 telehandler is a robust machine used for lifting, moving, and placing materials on construction sites. However, some operators have reported an issue where the telehandler does not move unless a function, such as the boom or tilt, is activated. This issue can cause delays in operations and may indicate an underlying problem with the drive system or other components. This article discusses potential causes of this issue and provides troubleshooting steps to resolve it.
Understanding the Problem: No Drive Unless a Function is Activated

1. Symptoms of the Issue
   The key symptom is that the GTH 644 telehandler is unable to drive or move unless one of its hydraulic functions (like the boom or tilt) is engaged. Once a function is called for, the telehandler moves normally. This suggests a possible issue related to the hydraulic system, electronic controls, or drive system that is preventing the machine from functioning as intended.
   
2. Potential Impact on Operations
   If this problem is not addressed, the telehandler's mobility will be compromised, leading to inefficiencies and potential safety risks. The issue affects the ease of operation, as the operator has to activate a hydraulic function every time they wish to drive the machine, which can be cumbersome and time-consuming.
   

Possible Causes of the Issue

1. Hydraulic System Pressure Issues
   The GTH 644’s drive system relies on the hydraulic system to function properly. If the system is not generating enough pressure or if there is an issue with the hydraulic pump, the machine may not engage the drive system correctly unless a function is activated.
   Solution: Check the hydraulic pressure to ensure it is within the manufacturer’s recommended range. Inspect hydraulic lines, pumps, and valves for any leaks or blockages that could cause a drop in pressure.
   
2. Electrical or Control System Malfunction
   The telehandler’s drive system is controlled by electronic components that manage various functions, including the hydraulic drive engagement. A malfunction in the electronic control system (such as a faulty sensor or control valve) could be causing the drive system to remain inactive until another function is called for.
   Solution: Inspect the electronic control system, including sensors, wiring, and fuses, for any issues. Perform a diagnostic check if the telehandler is equipped with one, and replace or repair any malfunctioning components.
   
3. Drive Motor or Transmission Issues
   If the drive motor or transmission is failing, the machine may not engage the drive system properly, especially if other hydraulic functions are working as expected. Internal issues within the transmission could result in a loss of power to the drive wheels, which may only be resolved by activating other hydraulic functions.
   Solution: Inspect the drive motor and transmission for signs of wear or damage. Check the oil levels in the transmission and replace any damaged components as needed. A transmission specialist may be required if internal issues are suspected.
   
4. Hydraulic Valve or Solenoid Issues
   A malfunctioning hydraulic valve or solenoid could cause the drive system to fail unless a function is activated. The solenoid valve controls the flow of hydraulic fluid to the various functions, including the drive system. If it’s not functioning properly, the hydraulic system may not engage the drive.
   Solution: Inspect the hydraulic valves and solenoids for any signs of failure. Ensure that they are clean and functioning correctly, and replace any faulty parts. Check for blockages or debris that may prevent proper fluid flow.
   
5. Low Hydraulic Fluid or Contamination
   Low or contaminated hydraulic fluid could cause intermittent issues with the drive system, as well as other hydraulic functions. If the fluid is not at the correct level or if it’s contaminated, the hydraulic system may not perform as expected.
   Solution: Check the hydraulic fluid level and condition. If the fluid is low or dirty, replace it with the manufacturer’s recommended fluid. Regularly inspect and change the hydraulic filters to prevent contamination.
   

Step-by-Step Troubleshooting Process

1. Step 1: Check Hydraulic Pressure
   Begin by checking the hydraulic pressure levels. Use a pressure gauge to ensure that the hydraulic system is generating the proper pressure. If the pressure is too low, this may indicate a pump issue, a leak, or a problem with the hydraulic fluid.
   
2. Step 2: Inspect the Electrical System
   Examine the electrical control system for any malfunctions. Look for blown fuses, faulty sensors, or damaged wiring. If your telehandler has diagnostic capabilities, use them to identify any error codes related to the drive system.
   
3. Step 3: Inspect the Hydraulic Valves and Solenoids
   Ensure that the hydraulic valves and solenoids are functioning correctly. If any valves are sticking or solenoids are not engaging properly, this could be the cause of the issue. Clean or replace any faulty components as needed.
   
4. Step 4: Check the Transmission and Drive Motor
   Inspect the transmission and drive motor for signs of wear or damage. If you notice any unusual noises, leaks, or a lack of movement, further investigation and possibly a professional repair may be needed.
   
5. Step 5: Check the Hydraulic Fluid Level
   Inspect the hydraulic fluid level and quality. If the fluid is low or contaminated, drain and replace it with the correct type of hydraulic fluid. Also, replace any dirty or clogged filters.
   

Preventive Maintenance Tips

1. Regular Fluid Checks
   Regularly check the hydraulic fluid levels and quality to ensure optimal system performance. Contaminated or low fluid can lead to reduced efficiency and cause intermittent issues like the one described.
   
2. Routine Inspections
   Perform routine inspections of the hydraulic system, drive system, and electronic components. Catching issues early can prevent more serious problems down the line and ensure that the telehandler is always ready for use.
   
3. Clean and Replace Filters Regularly
   Hydraulic filters should be cleaned and replaced at regular intervals to prevent contamination of the hydraulic fluid. A clogged filter can reduce fluid flow and cause problems with system performance.
   

Conclusion
The issue of no drive unless a function is called for in the GTH 644 telehandler can be caused by a variety of factors, including hydraulic pressure problems, electrical system malfunctions, transmission issues, or faulty hydraulic valves. By following a systematic troubleshooting process and checking each system component, operators can diagnose and fix the issue effectively. Regular maintenance, including fluid checks and component inspections, will also help prevent similar problems in the future, ensuring that the telehandler remains operational and efficient for daily tasks.