Yamaha FI Code 12: Crank Sensor — Causes & Fix
On Yamaha motorcycles and scooters, FI fault code 12 means the ECU is getting no signal from the crankshaft position sensor — the sensor that tells the ECU engine speed and position for spark and injection timing.
- Applies to
- Yamaha motorcycles
- Est. repair cost
- $25 – $160
- Time to fix
- 30–90 minutes
What it means
Common causes are a loose or corroded crank-sensor connector, damaged wiring, metal debris on the sensor, or a failed crankshaft position sensor. This is a generic Yamaha fuel-injection (FI) fault code, so it applies across Yamaha FI models — scooters and underbones like the Mio, NMAX, Aerox, and Sniper, plus YZF-R and MT motorcycles. Yamaha shows the code as a number on the diagnostic/odometer display, and the engine-warning light comes on. Once the fault is repaired and the ECU no longer detects it, the code clears; cycling the ignition (or using a Yamaha diagnostic tool) may be needed to confirm.
Symptoms
- Engine won’t start (blinking engine-warning light)
- FI code 12 shown
- Sudden cut-out while running
How to fix it
- 1
Inspect the crank sensor connector and wiring
1. Locate the crankshaft position sensor near the flywheel/crankcase. 2. Reseat the connector and check for corrosion or broken wires. 3. Clean any metal debris from the sensor tip.
- 2
Test or replace the sensor
1. Measure the sensor coil resistance against spec. 2. Replace the sensor if open, shorted, or out of range, then clear the code.
Frequently asked questions
Why won’t my Yamaha start with code 12?
Without a crank signal the ECU doesn’t know when to fire the spark or injector, so the engine can’t run. Check the sensor connector and wiring first.
Last updated July 15, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.