When the engine light comes on and stays on you can basically only do one thing, go to your local Honda dealer to get it fixed.
The engine light is an indication that ECU (Engine Control Unit) senses a problem that doesn’t compute. This could be a simple lambda sensor failure or something more complex… If you a bit technical you can check all connectors from and too the ECU, unplug them look for corrosion and reconnect them.
We normally spray the contact with Philips Contact Cleaner / Contact Spray with will prevent corrosion of plugs and socket contacts. WD-40 also has a product called Specialist Fast Drying Contact Cleaner – please not confuse this with the regular WD-40 spray you can find everywhere… Loctite has also a product called 7039 Cleaner / Reiniger – contact cleaner. From our experience the spray from Philips is the best, it’s not expensive and does exactly what the package says, also Philips being one of the biggest electronic companies in the world gives a bit extra motivation to buy it.
The Honda CBR250, CBR300 and CRF250L electronic contacts are well known to develop problems. For instance a dog daily urinating against your bike can, if the dog is the right height and your bike is at the right angle, disable your motorcycle within a week or two.
Also because the aluminum contact plugs used on the CBR250, CBR300 and CRF300 are untreated any high pH level will help corrosion, never use a cleaning product that uses nitric acid, or any acid, or ammonia. Salt and living near the sea will speedup corrosion. Some early CBR250, CBR300 and CRF250 models have connectors that consist of an aluminum plug being connected to a copper or brass socket which is a serious problem as aluminum galvanic corrosion occurs where there is metallic contact with a more noble metal. In a dry atmosphere, aluminum can be contact with brass and carbon steel with no risk of corrosion, but in Thailand we have a atmosphere where the humidity can go up to 90%….