Yamaha FI Code 42: Speed Sensor — Fix
On Yamaha motorcycles and scooters, FI fault code 42 means no normal signal is being received from the speed sensor — the sensor that reports road speed to the ECU and speedometer.
- Applies to
- Yamaha motorcycles
- Est. repair cost
- $20 – $130
- Time to fix
- 30–90 minutes
What it means
Common causes are a loose/corroded connector, harness damage, debris on the sensor tip, or a failed speed 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 42 with warning light on
- Speedometer erratic or dead
- Possible minor fuelling effects
How to fix it
- 1
Inspect the speed sensor and connector
1. Locate the speed sensor (gearbox/final drive). 2. Reseat the connector and clean any debris from the tip.
- 2
Check the signal and replace
1. Confirm the sensor pulses as the wheel turns. 2. Replace if dead, then clear the code.
Frequently asked questions
Why is my speedometer dead with code 42?
The same sensor feeds the ECU and the speedometer, so a circuit fault often knocks out the speed reading too.
Last updated July 15, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.