797F Off-Highway Truck Steering System: General Information

Electronic Technician Screens for the Steering System

"Configuration" screen for the Chassis ECM

The "Configuration" screen for the Chassis ECM shows a list of parameters. If the steering system on the machine is electronically controlled, then the "Value" for the "Steering Accumulator Charging System Installation" parameter must be set to "Installed".

"Override Parameter" screen for the Chassis ECM

Another screen within the Electronic Technician (ET) is the "Override Parameter" screen for the Chassis ECM. If the steering system on the machine is electronically controlled, then the "Value" for the "Steering Accumulator Charging Sol Current Override" parameter can be changed from 0 to 100 percent. The percentage represents a current value between 0 milliamperes to 1000 milliamperes. If 0 percent is entered as the "Value" for this parameter, then the Chassis ECM will send 0 milliamperes of current to the displacement solenoid for the steering pump. At 0 milliamperes, the steering pump is at the maximum displacement and the steering pump is at the maximum flow. If 60 percent or more is entered as the "Value" for this parameter, then the Chassis ECM will send 600 milliamperes or more of current to the displacement solenoid for the steering pump. At 600 milliamperes, the steering pump is at the minimum displacement and the steering pump is at the minimum flow.

Note: The setting for the high pressure cutoff valve for the steering pump can be checked at this point. Set the "Value" to 0 percent and operate the machine at HIGH IDLE. The engine speed and the steering accumulator pressure can be observed at the top of screen.

"Status" screen for the Chassis ECMGroup 6

The "Steering Accumulator Charging Solenoid Current" is one of the parameters that is shown on the group 6 "Status" screen for the Chassis ECM. If the steering system on the machine is electronically controlled, then the "Value" that is displayed for this parameter will change from 0 to 65.0 percent. The percentage represents a current value between 0 milliamperes to 650 milliamperes. If 0 percent is shown as the "Value" for this parameter, then the Chassis ECM is sending 0 milliamperes of current to the displacement solenoid for the steering pump. At 0 milliamperes, the steering pump is at the maximum displacement and the steering pump is at the maximum flow. If 65 percent or more is shown as the "Value" for this parameter, then the Chassis ECM is sending 650 milliamperes or more of current to the displacement solenoid for the steering pump. At 650 milliamperes, the steering pump is at the minimum displacement and the steering pump is at the minimum flow.

Machine Preparation for Troubleshooting

WARNING: Sudden movement of the machine or release of air or oil under pressure can cause possible injury or death to persons on or near the machine.To prevent possible injury or death, do the procedure that follows before testing and adjusting the Hydraulic System.

Move the machine to a smooth horizontal location. Move away from any machines that are working and any personnel.

Move the transmission shift lever to the NEUTRAL position. Activate the parking brakes.

Lower the body to the frame.

Stop the engine. Move the engine start switch to the OFF position.
Note: The pressure will not be released from the steering accumulators when you use the battery disconnect switch or the engine shutdown switch.

While the engine is not running, turn the steering wheel completely in both directions. Continue to turn the steering wheel in both directions until the front wheels will not move.

Turn the engine start switch key to the ON position. Do not start the engine. Turn the engine start switch key to the OFF position.
Note: This releases any pressure that is in the solenoid valve which is used to purge the accumulator. Refer to Operation and Maintenance Manual, "Steering Accumulator Pressure - Release" for more information.

Ensure that all of the oil pressure is released before any fittings, hoses, or components are worked on.

Permit only one operator on the machine. Either keep other personnel away from the machine, or keep other personnel in the view of the operator.

Place blocks in front of the wheels and behind the wheels.

Troubleshooting can be difficult. There is a list of possible problems on the following pages. In order to repair a problem, refer to the problem and the probable causes that are listed.

This list of problems and probable causes will only give an indication of the existence of a possible problem and of the repairs that may be required. There are sometimes more repairs or other repairs that are required beyond the recommendations that are in the list. Remember that a problem is not normally caused by only one part. A problem is usually caused by the relation of one part with other parts. This list can not provide all possible problems and all probable causes. The service person must find the problem and the source of the problem. The service person must then perform the necessary repairs.