- Blockages, restrictions, or kinks in hoses, lines or tubes
- Oil leaks in hoses, lines or tubes or at fittings
- Hydraulic oil viscosity is incorrect.
- Charge pump becomes too inefficient and cannot produce the required oil flow and pressures
- Steering solenoid connectors are not connected properly
- The hystat pump controls are suspect.
- The NEUTRAL setting for the hystat pump is improperly adjusted.
- The control lever is not calibrated properly.
- The speed sensors are not operating properly.
- The steering pedal position sensors are not calibrated properly.
- The electronic pressure override (EPOR) solenoids are not operating properly.
Note: Care must be taken in order to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the machine. You must be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component that contains fluid. Dispose of all fluids according to local regulations.
Blockages, kinks, or restrictions in both the supply and return oil lines can prevent oil flow to or from the hystat motor and can create unusual noises due to the high pressures involved. The hystat motor cannot turn without oil flow to the pump and from the pump. Check for these conditions on all hydraulic oil hoses, lines, and tubes in the steering system.
Check for leaks at all fittings and connections of hydraulic oil hoses, lines, and tubes in the system in question. Correct any problems that are found then retest for the symptom(s).
Leaks at fittings and connections on the pressure side of pumps are a direct source of oil loss in the system, which can lead to component failure if the low oil levels are not monitored and pumps and motors are starved of oil.
Leaks at fittings and connections on the suction side of pumps are a direct source of oil aeration, which can also cause cavitation damage to components and create excess or unusual noise as well.
Leaks at fittings and other types of hydraulic line connections can cause loss of oil flow and prevent components from attaining pressures necessary to perform work. Pressure losses generate complaints of weak force such as the blade tilt or the lift force and implements drifting while in the HOLD condition. Flow losses generate complaints of component speed such as the fan speed or the cylinder speed.
Ensure that oil is the correct viscosity for the operating conditions. In order to determine the correct oil viscosity, refer to the Operation and Maintenance Manual, "Lubricant Viscosities and Refill Capacities" for your machine.
Use a flow meter to test the flow rate of the Hystat Charge Pump. Refer to Testing and Adjusting, "Relief Valve - Test and Adjust" for your machine. If the charge pump becomes too inefficient and cannot produce the required oil flow and pressures, hystat pump will be slow to react, turns will not be as sharp, or the machine may not steer at all.
Ensure that the LEFT and RIGHT hystat pump solenoid connectors are not switched. If the connectors are switched (Left to Right and Right to Left), the machine will try to steer in the wrong direction. The monitoring system will detect this problem (via the speed/direction sensors in the hystat motor) and report an "INCORRECT TURN". Remove the connectors from the solenoids and replace the connectors to the proper position (Left to Left and Right to Right).
Ensure that the control solenoids for the hystat pump are operating properly. Refer to Troubleshooting, "Calibration" for your machine.
If a control solenoid for the hystat pump is not operating properly, the machine may not steer sharp enough, or may not steer at all in one direction. If the solenoid is shorted high, the machine may steer unexpectedly. An intermittent short in the solenoid or the wiring harness/connector can cause complaints of erratic operation.
Test the mechanical neutral position for the hystat pump control valve. Refer to Testing and Adjusting, "Calibration" and Testing and Adjusting, "Piston Pump Neutral - Adjust" for your machine.
If the neutral position of the hystat pump control valve is incorrect (off-center while in the NO STEER condition), the hystat pump control valve will command the actuator piston to move off-center when there is no hystat pump request. This condition may cause the machine to drive from straight line travel in a NO STEER condition, and may cause the machine to steer more sharply in one direction than the other.
Be sure that the control lever position sensor is calibrated properly. Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.
Check the status of the speed sensors in ET. Refer to Testing and Adjusting, "Speed Sensor - Adjust" for your machine. Replace the sensors, if necessary.
Be sure that the steering pedal position sensors are calibrated properly. Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.
Be sure that the EPOR solenoids are calibrated properly. Refer to Testing and Adjusting, "Transmission Drive Pump Pressure Override Calibration" for your machine.