A forklift parked with its mast half-stripped is not earning anyone money, and this 248-page Komatsu AX20 series service manual PDF (SM123) is how you finish the job on nine FG15 and FG18 lift truck configurations, HC and HT through ST and STLS. Wiring schematics in the appendix trace every circuit on the truck, a full hydraulic diagram maps the lift, tilt, and steering circuits, and the teardown chapters walk the Torqflow transmission, differential, wheel brakes, and power steering valve from removal through reassembly, ring gear backlash included. Check throttle position sensor 1 against its 0.6 volt released reading, then pull general hardware to 68.6 Nm (50.6 ft-lbs). Every hour you spend hunting a spec, the truck sits. Bookmarked, text-searchable, and printable, so your grease-stained copy lives on the bench while the PDF stays clean.
What's Inside This Komatsu AX20 Series Manual
| System | Pages | Key Topics |
|---|---|---|
| Introduction | 7-8 | AX20 Series Forklift Trucks, Maintenance Procedures, Computerized Sensors, Diagnostic Monitors, Repair Testing and Adjustment Procedures |
| Applicable AX20 EPA Lift Truck Models | 9-10 | FG15HC-17, FG15HT-17, FG15HTLS-17, FG15ST-17, FG15STLS-17, FG18HT-17, FG18HTLS-17, FG18ST-17 |
| Federal EPA Emission Control Statements | 11-14 | Identification Label, Warranty Rights and Obligations, Manufacturer Warranty Coverage, Owner Warranty Responsibilities, Emission-Related Parts |
| Safety | 15-45 | Safety Management, Safe Travel, Loading Operations, Stopping and Parking, Maintenance, Structure and Stability of the Lift Truck |
| General Information and Specifications | 46-54 | Specifications - Mast Data & Features - Indoor & Outdoor Trucks, Truck Data - Pneumatic Tire Lift Trucks, Truck Data - Cushion Tire Lift Trucks |
| Service Data | 55-59 | Gasoline Engine Trucks Pneumatic, Gasoline Engine Lift Trucks Cushion |
| Testing, Adjusting and Measuring | 60-76 | Adjust Ignition Timing, Adjust Spark Plug Gap, Adjust Valve Clearance, Adjust Fan Belt Tension, Measure Engine Cylinder Compression, Adjust the Parking Brake Lever |
| Inspection | 77-95 | Inspect Engine Starting Operation, Inspect Engine Running Condition, Inspect Air Cleaner Assembly (Cleaning the Filter Element) |
| Maintenance Operations | 96-102 | Lubricant List, Change Engine Oil and Filter - Gasoline/Lp Engines, Differential Case (Checking Differential Oil Level, Changing Differential Oil) |
| Engine Removal and Installation | 103-108 | Engine Removal, Engine Disassembly, Engine Installation, Motor Mounts |
| Transmission and Drive Axle Removal | 109-112 | Transmission Removal, Drive Axle Removal, Clutch/Torque Converter Removal |
| Clutch and Brake Master Cylinder Service | 113-127 | Clutch Disassembly, Clutch Assembly, Brake Master Cylinder, Bleeding Brake Lines |
| Steering Axle and Power Steering Valve | 128-158 | Steering Axle Removal, Steering Axle Disassembly, Power Steering Valve, Troubleshooting Steering |
| Wheel Brake and Differential Service | 159-197 | Wheel Brake Removal, Wheel Brake Disassembly, Differential Service, Ring Gear Backlash |
| Torqflow Transmission Service | 198-227 | Torqflow Transmission Disassembly, Control Valve, Hydraulic Circuit, Transmission Assembly |
| Masts | 228-248 | 35/40/50/55/60D-Md Series 2-Stage Masts, 30/35/40/50/55/60D-Ms 2-Stage Masts, 30/35/40/50/55/60D-Mt 3-Stage Masts |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| All Models | ||
| Throttle position sensor 1 (pedal released) voltage | Approx. 0.6V | p. 65 |
| Throttle position sensor 2 (pedal depressed fully) voltage | Approx. 4.5V | p. 65 |
| Accelerator pedal position sensor 1 voltage (at idle) | Approx. 0.6V | p. 66 |
| Accelerator pedal position sensor 2 voltage (at idle) | Approx. 0.3V | p. 66 |
| Tightening torque for general service | 50.6 ft/lbs. (68.6Nm) (7.0 kgfm) | p. 78 |
| Replacement interval | 6 months or 1,200 hours of operation | p. 77 |
| Air cleaner element replacement interval | Every 6 months or 1,200 hours of operation | p. 102 |
| Camber plate Camber | 0.045 in. (1.15mm) | p. 199 |
| Camber plate Load | 123.6 lbf/.035 in. (550N/0.9mm) | p. 199 |
| Engine Oil Capacity | 4.0 qts. (3.8 L) | p. 78 |
| Pneumatic tire trucks | ||
| Hydraulic Tank Capacity (Pneumatic tire trucks) | 8.2 gal (31 L) | p. 101 |
| Cushion tire trucks | ||
| Hydraulic Tank Capacity (Cushion tire trucks) | 5.8 gal (22 L) | p. 101 |
Komatsu AX20 Series Common Problems This Manual Covers
Komatsu FG15-17 forklift transmission clutch slipping, loses forward drive under load, sets 15SAL1 forward clutch fault
Check transmission fluid level and refill with 3.17 gal (12 L) after draining, page 100 covers the procedure. Run a stall test; readings outside 2,100 ± 100 rpm point to clutch or converter wear. Tear down per the Torqflow procedures on page 198 and measure clutch pack end gap against the 0.8 to 1.3mm spec on page 215.
Manual Section: Torqflow Transmission Service p. 198Engine cranks but won't start, runs rough and hunts at idle after sitting overnight
Pull the plugs and set gap to .031 - .035 in. (0.8 - 0.9 mm), the procedure on page 61 walks through it. Verify ignition timing and check valve clearance at .015 in. (0.38 mm), covered on page 56. Inspect the air cleaner element; replace it every 6 months or 1,200 hours regardless of appearance.
Manual Section: Testing, Adjusting and Measuring p. 60Hydraulic lift slow or weak under load, mast hesitates and drifts down when raised
Test main relief pressure at the valve; adjust to the 2,625 psi (18.1 MPa) set point listed on page 75. Check hydraulic oil level and condition, then inspect the suction line for collapse or air leaks. Trace the circuit against the hydraulic schematic on page 245 to isolate a leaking lift cylinder or worn pump.
Manual Section: Testing, Adjusting and Measuring p. 75Throttle sensor error E07 on display, engine stuck at idle and won't respond to pedal
Test throttle position sensor 1 with the pedal released; expect approximately 0.6V. Sensor 2 should read approximately 4.5V with the pedal fully depressed, both values on page 65. Verify accelerator pedal sensor 1 shows approximately 0.6V at idle per page 66, then inspect harness connectors for corrosion before replacing anything.
Manual Section: Testing, Adjusting and Measuring p. 65Brake pedal goes soft and spongy, pedal slowly sinks to floor when held
Inspect the master cylinder bore for scratches and corrosion, then bleed the brake lines following the procedure in the section starting on page 113. Pull the drums and measure lining thickness; replace shoes below 0.08 in. (2.0mm) and drums worn past 10.01 in. (256mm) inside diameter, both specs on page 85.
Manual Section: Clutch and Brake Master Cylinder Service p. 113Steering wanders and drifts at travel speed, wheel binds hard at full lock
Check tire pressures and kingpin play first, then inspect steering axle mounting hardware; snug loose general-service bolts to 50.6 ft/lbs (68.6 Nm) per page 78. Bleed air from the system and work through the power steering valve troubleshooting in the steering section starting on page 128, checking the spool for binding or scoring.
Manual Section: Steering Axle and Power Steering Valve p. 128Frequently Asked Questions
What is the tightening torque for the cylinder head mounting bolts on the Komatsu AX20 Series forklift?
The tightening torque for the cylinder head mounting bolts is 50.6 ft/lbs (68.6 Nm). This should be performed every 12 months or 2,400 hours of operation, whichever occurs first. p. 78
What is the specified torque for the oil pan drain plug on the Komatsu AX20 Series forklift?
The oil pan drain plug should be tightened to a torque of 21.7 - 28.9 lbs./ft (29.4 - 39.2 Nm). p. 98
What is the correct spark plug gap for the K21 engine in the Komatsu AX20 Series forklift?
The spark plug gap should be set to .031 - .035 in. (0.8 - 0.9 mm). p. 61
What is the required fan belt tension for the K21 engine?
The fan belt tension should be set to .43 - .51 in. (11 - 13 mm) of deflection when applying a pressing force of 22 lbf (98N) (10 kg). p. 62
What is the standard compression pressure for the K21 engine in a Komatsu AX20 Series forklift?
The standard compression pressure for the K21 engine is 178 psi (1,230 kPa) at 250 rpm. p. 63
How quickly can I access this Komatsu FG15HC-17 manual after buying?
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