What does the check engine light mean?

Modern cars have literally dozens of sensors around them to ensure that the engine is running safely, efficiently and not contributing unnecessarily to the car's tailpipe emission. If anything goes wrong with either the engine itself, or those many sensors, the check engine light on the dashboard can be triggered.

Think of it as a malfunction indicator lamp or an engine warning light, but don't ignore it. Th big question of course, is what does the engine light mean? Usually, it will be seen as an orange or yellow pictograph of an actual engine (as imagined by interior designers) and it means that something isn't right.

In the old days, cars had a limited range of warning lights, usually covering the oil, oil pressure and coolant temperature. But as the car became more and more electronically controlled (and efficient as a result) a need was seen to monitor all those controls and system. Ultimately, laws were made that forced carmakers to monitor these systems and to notify the driver – via the check engine light – if there was a problem at any point in the car.

As for what could cause the check engine light to come on, there are hundreds of possibilities. Perhaps it's a stretched cam-chain that has allowed the engine's crankshaft and valves to become out of synch (at the worst) or maybe it's just a sensor that reads the exhaust content that has stopped working (not so serious).

The point is, that single little malfunction indicator light covers a whole range of possible issues, some major, some minor, but all of them worth checking out when the little engine icon lights up on the dash. By the way, the icon won't usually be a flashing on and off warning, it'll just light up and stay lit until you do something about it.

It doesn't matter whether you drive an SUV like a Holden Captiva, or a conventional hatchback like a Ford Focus. Even owners of traditionally reliable brands like Subaru ad Toyota have seen this warning light.

So what do you need to do when the light flicks on? You don't need to stop driving the car. If there's a bigger problem, the car will itself go into limp-home mode or stop itself, so the check engine light is not an instruction to drop everything. But it does mean there will be a mechanic in your future, because the only way to know what the precise problem is is to have the car electronically scanned.

This involves hooking the car up to a computer so that it can have a conversation - computer-to-computer. Once that's done, the results can be decoded and a mechanic should be able to figure out what needs attention or replacing.

Ignoring the light means you might eventually do more damage to the car or, at the very least, be using more fuel than you should be and spewing out more emissions. There's one other reason not to ignore the check engine light, too; it's actually a roadworthy fail if the light is illuminated.