Step-by-step electrical diagnosis for Yamaha Error Code 12, resistance specs for the SMG stator and CKP sensor, and related OE part numbers.
In over 80% of Error Code 12 cases on Smart Motor Generator (SMG) models, the Crankshaft Position Sensor (CKP) and stator windings are still intact — the culprit is high contact resistance or melting at the white 3-pin phase connector under the right side cover. Only replace the stator/rotor assembly if phase resistance or insulation to ground fails spec.
| Test Point | Normal Specification (20°C) | Failure Symptom | Recommended Action |
|---|---|---|---|
| 3-Pin White Phase Connector (W-R-B) | < 0.05 Ω contact drop, no discoloration | Melted plastic housing / blackened pins | Replace with high-amp waterproof connector or direct solder |
| Stator 3-Phase Winding Resistance | 0.072 – 0.088 Ω between any two phases | Open circuit (OL) or continuity to ground | Replace Stator Assy if shorted to engine ground |
| CKP Hall Sensor 6-Pin Plug | 5V reference stable, clean terminals | Water ingress / bent female pin | Clean with contact cleaner & pack dielectric grease |
| Flywheel Rotor Assy Magnet Track | Clean magnetic trigger ring, no scoring | Metal debris bridged across hall trigger track | Clean debris; replace Rotor Assy (B74-H1450-00-00) if cracked |
Because the SMG system uses the stator as the starter motor, cranking draws 60–90A through the 3 phase wires. Any terminal corrosion melts the plug and triggers Code 12.
Unplug the 3-pin connector and test continuity between each stator wire (White, Red, Blue) and the crankcase. Any continuity means the stator winding insulation is burned.
After repairing the connector or stator, confirm battery charging voltage reaches 14.0–14.5V DC at 5,000 RPM.
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