Yamaha FI Code 24: O2 Sensor — Causes & Fix
On Yamaha motorcycles and scooters, FI fault code 24 means the O2 (oxygen) sensor is inactive or sending no normal signal — the sensor the ECU uses to trim the mixture for clean, efficient running.
- Applies to
- Yamaha motorcycles
- Est. repair cost
- $25 – $150
- Time to fix
- 30–90 minutes
What it means
Typical causes are a loose/corroded connector, an exhaust leak upstream of the sensor, damaged wiring, or an aged/failed O2 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
- FI code 24 with warning light on
- Worse fuel economy
- Mild running roughness; may fail emissions
How to fix it
- 1
Inspect connector and exhaust
1. Find the O2 sensor in the exhaust header. 2. Reseat the connector; check for exhaust leaks before the sensor.
- 2
Test and replace
1. Check the sensor and its heater circuit. 2. Replace an aged or dead sensor, then clear the code.
Frequently asked questions
Can I ride with code 24?
Usually yes for a while — the ECU uses a preset map — but economy suffers. Replace the sensor when you can.
Last updated July 15, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.