769D Off-Highway Truck: Steering System Troubleshooting PART 2

Problem : The steering piston pump does not destroke to standby pressure.

Probable Cause

• Sticking spool in the flow compensator valve
• High pressure setting of the flow compensator valve

(1) Pin (2) Drive (3) Timing Mark (4) Gerotor star valleys (A) Reference Line (B) Reference Line(C) Reference Line

• Timing mark (3) that is on drive (2) must fall on the parallel line between any two gerotor star valleys (4) .

Note: Reference lines (A), (B) and (C) are parallel.

Problem : Soft steering.

Probable Cause

• Air in the steering hydraulic circuit
• Low oil level in steering hydraulic tank

Check The Warning System (Steering System)

(5) Action light (6) Secondary steering indicator (7) Secondary steering alert indicator(8) Brake release and secondary steering control



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

2. Turn the parking brake control to the OFF position.Note: When the parking brake control is in the ON position, friction will not allow the secondary steering system to turn the wheels all the way to the steering cylinder stops.

3. Turn the engine start switch key to the ON position.

4. The Caterpillar Monitoring System action light (5) should flash and the action alarm should sound for approximately three seconds. Secondary steering indicator (6) is activated and the electric motor for the secondary steering and brake electric drive pump must operate for three seconds.

5. The secondary steering and brake electric drive pump will operate when the secondary steering indicator light (6) is ON. When the secondary steering system is used to steer the machine, more steering effort will be needed. The primary steering system will require less steering effort.

6. Start the engine. Secondary steering alert indicator (7), action light (5), and the action alarm should turn off after three seconds.

7. Operate the engine and move secondary steering and brake release control (8) to the MANUAL position. Secondary steering indicator (6) should activate. The steering system must operate in the same way as normal steering operation. Secondary steering alert indicator (7), action light (5), and the action alarm should not activate.

8. Move secondary steering and brake release control (8) to the AUTO position and turn the engine start switch key to the OFF position.

9. Turn the parking brake control to the ON in order to apply the parking brakes.

Problem : Monitoring system, lights, action alarm, and starter does not operate.

Probable Cause

• The battery disconnect switch is in the OFF position.
• Low battery voltage

Problem : The secondary steering alert indicator, the action light, and the action alarm are activated after the engine starts. The secondary steering indicator and the electric motor is OFF.

Probable Cause

• The Power Train Electronic Control Module (Power Train ECM) is not receiving voltage from the "R" terminal on the alternator.
• Bad Cat Data Link
• Bad Power Train ECM
• Bad Caterpillar Monitoring System

Problem : Secondary steering alert indicator, action light, action alarm, secondary steering indicator, and the electric motor are ON.

Probable Cause

• Bad steering pump oil pressure switch
• Low oil in the steering hydraulic tank
• Bad Power Train ECM

Problem : Secondary Steering alert indicator and the action light flashes until the engine starts. Secondary steering indicator and the electric motor are OFF.

Probable Cause

• Open circuit or shorted circuit to ground on secondary steering relay that is mounted on the frame
• Open circuit or shorted circuit to ground on secondary steering relay that is mounted in the cab
• The contacts are corroded or the contacts have failed to open on the secondary steering relay that is mounted on the frame.
• Open circuit type failure from the positive "+" battery terminal to the secondary steering pump oil pressure switch terminal
• Open circuit type failure from the secondary steering relay that is mounted on the frame to the secondary steering and brake release electric drive pump
• Open circuit type failure from the electric motor to the negative terminal on the battery
• Failure of the electric motor
• The secondary steering and brake release electric drive pump will not turn.
• Bad Power Train ECM

Problem : Secondary steering alert indicator does not flash during engine start-up.

Probable Cause

• Bad Cat Data Link
• Bad Power Train ECM
• Bad Caterpillar Monitoring System
• Bad steering pump oil pressure switch

Problem : Secondary steering alert indicator and the action light flashes. Secondary steering indicator and the electric motor operates after the engine starts.

Probable Cause

• Bad Power Train ECM

Problem : Secondary steering indicator does not turn ON and the electric motor does not operate when the secondary steering and brake control is placed in the Manual position.

Probable Cause

• Bad secondary steering and brake release control
• Open circuit between the secondary steering fuse and the secondary steering and brake control
• Open circuit between the secondary steering and brake release control and the secondary steering relay that is located behind the cab

MARYGAR

769D Off-Highway Truck: Steering System Troubleshooting PART 2 2012-12-04T16:33:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown