John Deere 6020 to 6620 Tractor Repair Manual

Check the fuel filters first and bleed the injection system as shown in the Fuel, Air Intake, Cooling and Exhaust Systems section. If the filters are clear, test the Lucas or Bosch VP44 injection pump for delivery pressure and timing. A blocked pre-filter or contaminated pump is the most common cause of a no-start after the tractor has been sitting, and the section provides the full bleeding procedure and pump service steps to restore clean fuel delivery and smooth combustion.

Check the hydraulic oil level and condition first, then test pump output at the test port as described in the Hydraulic System section. Worn axial piston pump internals or a clogged suction strainer are the usual causes of low system pressure. If pump output is within spec, trace the selective control valve for a stuck spool or failed solenoid before condemning the pump, as the section covers both hydraulic and electrohydraulic control variants with the pressure test values and spool inspection procedure.

Inspect the cooling system as outlined in the Fuel, Air Intake, Cooling and Exhaust Systems section: check coolant level and condition, pressure-test the system for leaks and test the thermostat. A failed water pump is a known failure point on this series - replace it on any evidence of weeping from the shaft seal or reduced coolant flow. Clean the radiator core and the air pre-cleaner before assuming a deeper engine fault, then verify fan belt tension and radiator cap pressure rating.

On SynchroPlus transmissions, low transmission oil pressure from a worn pump or blocked suction strainer is the typical cause of gear slip under load. On PowrQuad and AutoQuad units, worn electrohydraulic clutch packs cause sluggish or refused shifts as line pressure drops. The transmission sections cover clutch pack removal, wear measurement and replacement, and the calibration procedure required after reassembly to restore correct shift pressure and timing across the full gear range.