2004–2005 Yamaha Majesty 400 YP400(S) Factory Service Manual (P/N 5RU1-AE1)

• A 443-page, two-manual Yamaha Majesty 400 PDF set: 2004 YP400(S) Service Manual, Manual No. 5RU1-AE1 — 417 pages; 2005 YP400(T) Supplementary Service Manual, Manual No. 5RU1-AE2 — 26 pages. Coverage is for model codes 5RU1/5RU3 and 5RU6/5RU8, respectively.
• Engine repair coverage runs from removal and installation through camshaft and timing-chain work, cylinder-head and valve service, piston inspection, oil-pump service, and crankshaft, balancer, journal-bearing, and transmission work.
• V-belt automatic transmission and centrifugal clutch procedures cover primary and secondary sheave removal, inspection and reassembly, clutch-shoe checks, spring-controlled secondary-sheave work, and belt installation.
• Chassis and cooling procedures address wheel and brake-disc service, master cylinders and calipers, hydraulic brake bleeding, front-fork overhaul, steering-head and swingarm work, plus the radiator, thermostat, water pump, and oil cooler.
• FI and electrical diagnosis includes ECU diagnostic mode, fault-code and fail-safe tables, injector, fuel-pump, TPS, and ISC checks, and circuit troubleshooting for ignition, starting, charging, lighting, signaling, cooling-fan, and immobilizer systems.
• The 2005 supplement distinguishes the dual-front-disc and oil-coated-paper air-filter build from the 2004 single-disc/wet-element specification. It also provides revised cable routing and separate left/right crankshaft journal-bearing selection and must be used with the 2004 base manual.

Both Yamaha factory volumes are first editions: the base manual is dated December 2003, and the supplement September 2004. Yamaha produced them primarily for its dealers and qualified mechanics and assumes basic mechanical knowledge and repair technique. The set is therefore suited to trained technicians and experienced mechanics comfortable with specialty tools and factory test data.

Engine, Drive, and Chassis Repair

The engine chapters cover the liquid-cooled 394.9 cc DOHC single from removal through top-end and crankcase work. Camshaft timing, the decompression system, valve guides and seats, piston and ring inspection, the oil-pump drive, crankshaft and balancer assemblies, journal bearings, starter clutch, generator, and final-drive transmission all receive dedicated procedures. Exploded assembly views and job-order charts support the larger removal and disassembly sections.

Belt-drive work goes beyond routine V-belt replacement. The manual details the primary and secondary sheaves, sheave weights, clutch shoes and housing, secondary-sheave bearings and seals, and controlled spring compression during disassembly and reassembly. Chassis repair covers static wheel balancing, brake-pad and disc inspection, master-cylinder and caliper overhaul, fork seals, bushings and damper rods, the lower bracket and steering bearings, rear shocks, and the swingarm.

Cooling-system coverage handles radiator and cap testing, thermostat inspection, and water-pump mechanical-seal and oil-cooler work. The maintenance chapter adds valve-clearance and exhaust-gas adjustment, compression and ignition-timing checks, engine and transmission oil service, coolant replacement, steering-head adjustment, hydraulic brake bleeding, battery charging, and headlight aiming.

Fuel Injection, Electrical Systems, and Diagnostics

The FI chapter maps the ECU, fuel pump and injector, throttle body, throttle-position and intake-pressure sensors, temperature sensors, lean-angle switch, speed sensor, and idle-speed control valve. Its meter-operated diagnostic mode can display sensor output and command actuators without separate measuring equipment. Fault-code, fail-safe, reinstatement, and symptom-based troubleshooting tables guide circuit and component isolation.

Electrical repair sections provide component locations and circuit-level checks for ignition, the starter cut-off circuit and starter motor, A.C. magneto charging, the rectifier/regulator, lights, signals, and radiator-fan control. The immobilizer section covers system diagnosis, key-code registration, stored malfunction codes, and which registrations are required after ECU, immobilizer-unit, main-switch, or accessory-lock replacement.

Factory Data, Tools, and Diagrams

Specifications are organized by engine, chassis, and electrical system, with general tightening guidance, engine and chassis torque tables, fluid and lubrication data, wear limits, clearances, adjustment data, and electrical test values. Useful diagram sets include the full YP400(S) wiring diagram, FI wiring diagram, cooling-system diagrams, air-induction-system diagrams, electric starting-system circuit diagram, and immobilizer system and circuit diagrams. Detailed cable-routing views locate the wire harness, brake hoses, throttle cables, speed-sensor lead, and charging-system leads.

The special-tool schedule gives Yamaha 90890-series numbers and the YM/YU/ACC alternatives supplied for the U.S. and Canada. Notable examples are the sheave spring compressor 90890-04134 with fixed block 90890-04135, fuel-pressure gauge 90890-03153 with adapter 90890-03181, and plane-bearing installer/remover 90890-04146.

The manual warns that grease must not contact the V-belt or secondary sheave, where contamination can impair drive operation. When splitting the crankcase, hammer contact is limited to reinforced areas; striking the mating surfaces can damage the sealing interface. Fuel-pressure testing, hydraulic brake work, and spring-loaded clutch service call for trained handling, secure support, and the specified service equipment.