2005–2012 Honda TRX400EX and TRX400X ATV Factory Service Manual

This Honda factory service manual covers the 2005–2012 TRX400EX and TRX400X ATVs. Model identification distinguishes A (U.S.), CM (Canada), and U (Australia, New Zealand, and European Direct Sales) destination codes.

Text search, navigation, and wiring detail: An OCR text layer supports searches through the service chapters, although some table entries and diagram labels are missed and the cover has no searchable text. Chapter bookmarks provide direct navigation. Small wire-color and connector labels on the wide wiring diagram require zooming.

• Engine repair: Engine removal and installation, cylinder-head and valve service, cylinder/piston inspection, crankcase separation, and crankshaft/balancer work.

• Clutch and transmission: Wet-clutch overhaul, gearshift linkage repair, transmission inspection, and reverse-lock mechanism inspection and adjustment.

• Fuel and lubrication: Carburetor disassembly, pilot-screw adjustment, high-altitude settings, and oil-pump, oil-cooler, oil-strainer, and oil-tank service.

• Brakes and chassis: Hydraulic disc brake bleeding and overhaul, wheel-bearing replacement, steering-shaft service, suspension arms, rear axle, swingarm, and shock linkage.

• Electrical diagnosis: Alternator and starter-clutch service, AC-CDI ignition tests, electric-starter troubleshooting, lights/switches checks, wiring diagrams, and cable/harness routing.

Honda wrote this manual for qualified professional technicians with appropriate service training, tools, and shop equipment.

Engine Repair and Dry-Sump Lubrication

The air-cooled 397cc single-cylinder engine sections cover valve-guide replacement, valve-seat refacing, camshaft/decompressor inspection, and cam-chain timing. Cylinder-compression testing accounts for the automatic decompressor's effect on the reading.

Lubrication service: The Lubrication System Diagram accompanies oil-pump relief-valve checks, rotor-clearance inspection, and strainer servicing. The manual warns that installing the oil filter backward can cause severe engine damage.

Maintenance data includes intake and exhaust valve clearances, DPR8Z/DPR9Z spark-plug specifications, oil-change capacities, wear limits, and component-specific torque tables.

Transmission, Clutch, and Reverse System

The manual separates in-frame clutch service from work on the five-speed transmission with reverse or the crankshaft, which requires engine removal and crankcase separation. Internal inspection covers the shift forks, shift drum, gear/bushing clearances, and crankshaft-to-balancer timing.

Clutch procedures identify holder 07724-0050002 and U.S. alternative 07724-0050001. The reverse-switch and ignition control module (ICM) sections explain the starting interlock and reverse-speed limiter, helping technicians distinguish normal reverse lockout from an ignition fault during a no-start diagnosis.

Carburetor Inspection and Adjustment

The carburetor section covers the accelerator pump, air cut-off valve, float valve, jets, and throttle linkage, supported by an exploded assembly drawing. It includes the idle-drop pilot-screw procedure and high-altitude carburetor changes.

Float inspection specifies assembly replacement when the level is outside tolerance. Tightening the pilot screw against its seat can damage the seat, a specific caution addressed in the disassembly and adjustment procedures.

Chassis and Hydraulic Disc Brakes

Chassis repair covers front wheel hubs, double-wishbone front suspension, the rear swingarm, axle bearing holder, and steering tie-rods. Rear axle instructions distinguish actual tightening torque from the wrench reading when the specified locknut tools are used.

Front and rear brake sections detail master-cylinder and caliper inspection, piston/seal renewal, parking-brake service, and pad/disc checks. Shock-absorber coverage addresses removal, pivot bearings, and assembly replacement; detailed preload and damping adjustments are referred to the owner's manual.

Electrical Tests and Wiring References

Charging diagnosis includes battery load testing, current-leakage checks, alternator charging-coil inspection, and regulator/rectifier circuit checks. AC-CDI testing covers ignition-coil, exciter-coil, and ignition-pulse-generator peak voltage; the tool list specifies the U.S. IgnitionMate tester MTP07-0286.

Separate Battery/Charging System, Ignition System, and Electric Starter diagrams accompany connector-terminal checks and starter-motor brush/armature inspections. The wide Wiring Diagram, marked 0030Z-HN1-A400, provides wire-color codes and switch-continuity charts for tracing lighting, starting, and ignition circuits.

Troubleshooting charts also address hard starting, power loss, poor idle/high-speed performance, and handling faults.

Suspension springs store energy, and brake contamination reduces stopping power; follow Honda's safety precautions and use appropriate protective equipment.

English PDF and Included Pages

Supplied as one printable 344-page PDF in English, including one cover page, three preliminary pages, and eight Memo pages. The wide wiring-diagram sheet is also included in that total.