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Home / Wheel Loaders / Kubota Wheel Loaders / Kubota R420S

Kubota R420S Troubleshooting

The Kubota R420S wheel loader is powered by 91.4 cu.in (1.5L) Kubota D1503-M-TE3 three-cylinder indirect injection turbocharged diesel engine with a rated power of 39 hp (29 kW) at 2600 rpm. The Kubota R420S is equipped with a hydrostatic transmission, power steering system, wet disc brakes, and 12.5/70x16 standard tires. The hydraulic system has a pump with fluid flow rate of 11.1 gpm (42.1 lpm). The hydraulic pressure is 3000 psi (206 bar). The wheel loader has a rated operating capacity of 1915 lbs (870 kg) and tipping load of 3830 lbs (1740 kg). The max lift height is 110.6 inches (2810 mm) to hinge pin, and boom breakout force is 6560 lbs (2980 kg).

Engine Troubleshooting

Engine hard to start or doesn't start
Air in the fuel pipes - Bleed the fuel pipes.
Fuel filter element is clogged - Install new filter element.
Clogged or burnt injection nozzle - Check and replace nozzles if required.
Dirt or water in fuel system - Drain water or flush dirt from the system.
Valve out of adjustment - Adjust valve clearance.
Fuel injection pump failure - Change or repair the pump.

Diesel starts and suddenly stops
Air cleaner is clogged - Clean or replace air cleaner element.
Clogged fuel filter - Service or replace the filter.
Poor fuel injection pump tightness - Look for any leaks of fuel pump, tighten it fast.
Fuel injectors are faulty or clogged - Clean fuel injectors or change it.
Fuel injection pump is defective - Replacement or repair required.

Diesel shuts off while driving
Engine is not fully warmed up - Warm up engine as required.
Fuel filter element clogging - Clean or replace the filter.
Air in the fuel pipes - Bleed the fuel pipes.
Fuel injection nozzles fault - Install a new kit of correctly balanced nozzles.
Fuel injection pump timing is wrong - Use the correct fuel injection pump timing adjustment.

Engine stalls at idle
Low idle speed set incorrectly - Adjust low idle speed.
Fuel injection pump is damaged - Repair or replace injection pump.
Damaged or clogged injectors - Change or clean fuel injectors.
Valve out of adjustment - Adjust valve clearance.

Loss of engine power
Air filter is clogged - Change or service air filter element.
Defective injection nozzle - Inspect nozzles and replace if necessary.
Fuel injection pressure is wrong - Adjust to proper pressure.
Incorrect valve clearance - Adjust to proper valve clearance.
Low idle speed adjustment is incorrect - Normalize low idle speed.
Fuel hoses or lines are clogged - Fuel lines and hoses need to be cleaned.
Cylinder head gasket is defective - Install new cylinder head gasket.
Leaking or defective piston rings - Piston rings replacement required.

Engine overheating
Insufficient coolant fluid - Add coolant fluid to cooling system and also check it for leaks.
Engine oil level is low - Fill up the oil to required level.
Defective radiator cap or clogged radiator core - Clean radiator or change cap.
Fan belt is loose or defective - Replace the fan belt.
Diesel engine is overloaded - Load reducing required.

Insufficient oil pressure
Lack of oil - Add oil to the engine crankcase.
Plugged engine oil filter - Clean or change engine oil filter.
Different type of engine oil - Use oil of correct viscosity.
Excessive main bearing oil clearance - Change bearings.
Defective oil pump - Remove and inspect oil pump.

Engine knocking sound or abnormal noise
Engine oil level is low - Fill the crankcase with engine oil.
Low coolant temperature - Warm up to required temperature.
Wrong setting of fuel injection pump timing - Set the fuel pump timing correctly.
Wrong adjustment of low idle speed - Normalize low idle speed.
Fuel injectors are faulty or clogged - Replace fuel injectors.
Faulty or misaligned connecting rod - Align or change connecting rod.
Worn or broken pistons - Replace the pistons as required.

Hydrostatic Transmission Troubleshooting

HST transmission is making noise
Dirty transmission fluid or insufficient fluid level - Pour fresh fluid or add transmission fluid to proper level.
Worn or out of adjustment speed control linkage - Adjust or repair linkage.
Relief valve failure - Install a new relief valve.
Excessive transmission load - Reduce transmission load.
Worn or defective parts of the hydrostatic transmission - After disassembling and inspection, change defective components.

Loss of power
Low oil level - Check transmission oil level and add oil as required.
Relief valve is damaged - Replace relief valve as required.
Speed control pedal linkage is bent or not adjusted - Adjust or change linkage.

Hot transmission oil
Transmission oil insufficient - Need to add transmission oil.
Dirty transmission oil filter element - Clean or replace the transmission filter.
Clogged or damaged cooling components - Check all cooling components and change or clean if required.
Transmission is under excessive load - Reduce loading.

Transmission oil leaking
Seals or gaskets are broken - Seals and gaskets need to be replaced.
High internal transmission case pressure - Repair or replace damaged components.
Oil drain pipe is plugged - Check pipe and service if necessary.

Hydraulics Troubleshooting

Hydraulic system is overheated
Hydraulic pressure incorrectly adjusted - Set pressure correctly.
Main relief valve malfunction or improper adjustment - Replace or set up the relief valve.
Dirty hydraulic oil - Change hydraulic oil.
Hydraulic oil level is low - Fill up the hydraulic oil.
Worn hydraulic oil pump - Install new pump or repair it.

Lift arm won't raise or lower
Defective lift controls - Replace or repair.
Hydraulic pump is broken - Replace or repair pump if necessary.
Defective hydraulic control valve - Replace or repair the valve.
Damaged hydraulic cylinder - Change or repair lift cylinder.
Low hydraulic fluid level - Checking hydraulic fluid level and add if necessary.

Bucket tilt does not work
Defective bucket controls - Inspect and repair if necessary.
Hydraulic pump not working - Install new pump or repair it.
Hydraulic control valve is faulty - Replace or repair the valve.
Faulty hydraulic bucket cylinder - Change or repair cylinder.
Hydraulic fluid level low - Fill up the hydraulic fluid.

Bucket or lift arm is working slowly
Hydraulic pump is defective - Check the pump capacity and replace pump if required.
Hydraulic cylinder leaking - Repair leak by replacing the seals.
Low hydraulic fluid level - Fill the system to proper hydraulic fluid level.
Hydraulic control valve is defective or set improper - Set correctly or repair.
Hydraulic pressure is low - Adjust it correctly.

Lift arm or bucket is jerky
Air in the hydraulic system - Bleed air from hydraulic system.
Hydraulic oil filter element is clogged - Clean or replace the filter.
Contaminated hydraulic oil - The oil must be changed.
Scored cylinder tube or rod - Change failed component.

Hydraulic pump makes excessive noise
Lack of oil or hydraulic leakage - Add hydraulic oil or correct system leaks.
Hydraulic filter is dirty - Clean or install new filter.
Suction line clogging - Need to clean the suction line.
Pump sucks air - Need to bleed air.
Worn pump components - Rebuild or install new pump.

Electrical Troubleshooting

Battery will not charge
Electrical wire connections are loose or corroded - Clean or tighten wiring connections.
Battery terminal clamps are defective - Terminal clamps need to be replaced.
Worn-out battery - Battery change required.
Belt is damaged or loose - Need to adjust belt tension or replace belt.

Starter motor turns slow
Low battery output voltage - Battery needs to be recharged.
Battery discharges quickly - Battery needs service or replacement.
Terminals are faulty or battery cables are disconnected - Check cable connections and replace or service terminals.

Starter motor is not working
Battery is discharged or defective - Recharge or replace battery.
Battery cables are disconnected or improperly connected - Inspect cables and connect properly.
Battery voltage is low - Charge the battery.
Defective starter motor - Starter needs to be replaced.

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WHEEL LOADERS SPECIFICATIONS

Wheel Loaders, Skid Steers, and Compact Track Loaders