Engine warning light (check engine, MIL) is on or flashing

The engine warning light, often marked FI or shown as an engine symbol, is the ECU's way of telling you it has found a fault in the fuel injection or ignition system and stored a code. It is not the same as the oil, temperature or ABS lights. On most bikes it should light for a moment at key-on as a bulb check, then go out once the engine runs. If it stays on, comes on while riding, or flashes, read the code.

Is it safe to ride?

With care, if the engine runs normally: ride gently to where the code can be read. If the light flashes, or the engine misfires, loses power or runs hot, stop and get it checked: a flashing light on many bikes means misfiring that can damage the catalytic converter.

Quick checks first

• Is it really the engine light, not the oil, temperature, battery or ABS light?
• Does it come on at key-on and go out after starting? That is normal.
• Did it come on after washing, rain, or work on the bike (a connector left off)?
• Is the battery in good condition?
• Does the engine run differently?

Diagnose it step by step

1At key-on, before starting, does the light come on?

• No, never: the system may have no power, or the bulb or LED has failed. The K-Light 125 manual says to check the fuse, earth wire and ECU plug first. See Check fuses and relays and Clean and tighten earth connections.
• Yes: go to step 2.

2After starting, does it go out within a few seconds?

• Yes: normal. No fault stored.
• No, or it comes on while riding: go to step 3.

3Is it flashing, or is the engine misfiring, losing power or overheating?

• Yes: stop riding hard. Ride slowly to safety or have it collected. Go to step 4.
• No: go to step 4 when convenient.

4Read the stored codes.

• Read engine fault codes. Write every code down before clearing.

5What does the code point to?

• Sensor (throttle, intake pressure, temperature): Check the engine sensors.
• Oxygen sensor or its heater: Check the oxygen sensor.
• Injector: Check the fuel injector.
• Fuel pump: Check the fuel pump.
• Ignition coil or crank sensor: Ignition coil test, Pick-up test.
• ECU internal error: Diagnose a suspected CDI or ECU fault.

6. Before replacing any part, clean and check its connector and earth. Most "sensor" codes are caused by connectors, water and earths: Clean and seal electrical connectors.

7. Does the code not match the symptoms, or keep changing? The K-Light 125 manual says an unstable earth wire can cause this. Fix the earth, disconnect the battery for 3 minutes, reconnect and start. Check the battery: Test and charge a 12 V battery. Low voltage gives false codes.

Causes, most likely first