Engine Malfunction Lights

[WIL35]

On our Toyota Avensis Verso the Engine Malfunction light recently came on, I thought it would be the other lambda sensor, but it went off again a few days later. I thought these needed to be reset (or battery disconnected) to get them to go out. If it isn't a Lambda sensor giving up up, what else could cause the light to come on temporarily? During this time the car has been running perfectly well.

Thanks.

[annodomini2]

There are 2 lights, one will be red, the other yellow.

The yellow one typically indicates minor fault and sometimes causes limp home mode.

The red one, known as MIL and typically the car will allow you to keep driving in limp home until you stop the engine, or cut out completely, then typically won't restart.

The yellow one, if the fault is not observed for X more starts/stops it'll clear the fault and the lamp (there's usually a min mileage to stop you just starting and stopping the engine)