Checking Level Control Pressure Oil Pump

NOTE: Numbers in parentheses ( ) indicate a component or tool in the associated illustration.

WARNING:
^ Risk of Injury to skin or eyes due to hydraulic fluid spraying out under high pressure
^ Risk of poisoning due to consuming hydraulic fluid

NOTE:
^ Before starting work on the hydraulic system, depressurize the system
^ Wear protective clothing and safety gasses

1. Empty pressure oil system at rear axle
2. Connect tester to rear axle connecting piece (57)
3. Pour suitable oil into oil reservoir (2)

NOTE: For testing, increase the quantity of oil to approx. 0.5 liters above the "max. " marking (a) on the oil dipstick (2a)

4. Disconnect return (flow) line (T) at oil reservoir (2), connect oil drain hose (061) to the return (flow) line (T) and guide into oil reservoir (2)
- Pay attention to secure hose routing
- When the pressure relief valve in the valve unit opens, the oil pressure in the return (flow) line increases to approx. 2 bar
5. Connect Hand-Held Tester (HHT) (089) part No. 65 11 0001 99, or equivalent, with suitable test cable (094) to data link connector (X11/4)

WARNING:
^ Risk of accident due to vehicle starting off automatically when engine is running
^ Risk of injury due to being trapped and burns when intervening while starting the engine or when the engine is running

6. Start engine and allow to idle

WARNING:
^ Secure vehicle to prevent it from starting off automatically
^ Wear close-fitting, tight clothing
^ Do not touch hot or rotating parts

7. Place HHT (089) in "lift" position

NOTE:
^ Only carry out the test briefly due to the high pressures.
^ The delivery pressure of the pressure oil pump is limited by the bypass valve in the valve unit

8. Check opening pressure of bypass valve
- Delivery pressure at engine idle speed: 180-190 bar
9. Check delivery rate of pressure oil pump:
- Connect oil drain hose (061) to the return (flow) line (T) in a measuring vessel
- Ensure that there is sufficient oil in the oil reservoir.
- The pump must not draw in air under any circumstances
- Delivery rate at engine idle speed: 0.2 liters/min
10. If not to specifications:
- If the opening pressure of the pressure relief valve and output is clearly not achieved at idle speed, replace pressure oil pump/tandem pump
- Insufficient pressure at optimum delivery rate, replace valve unit
- When the delivery rate is not achieved, replace pressure oil pump/tandem pump
- When the delivery rate is exceeded and output is not achieved at idle speed, replace valve unit
11. Switch off engine
12. Disconnect HHT with test cable

WARNING:
^ Risk of injury to skin or eyes due to hydraulic fluid spraying out under high pressure
^ Risk of poisoning due to consuming hydraulic fluid
^ Wear protective clothing and safety glasses

13. Disconnect tester on distributor fitting (57)
14. Connect return (flow) line (T) to oil reservoir (2)
15. Fill pressure oil system at front and rear axle