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On-board sensors are there to make sure that the car stays within the parameters of emissions standards.

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Cars have more warning lights than you can shake a stick at. The lights are helpful, especially for those who don't monitor or maintain their vehicles regularly. The most useful may be the low tire pressure indication – few motorists bother to check pressure until the tire is visibly flat.

The most perplexing dash light, by far, is the "check engine," which can be illuminated by a multitude of causes, none of which the average person will know until a diagnostic tool is plugged in to the vehicle. For motorists who don't own one, this means a trip to the shop.

In the old days, when the light came on, it meant an oil problem and impending doom for the engine. Now it's all about sensors and an $800-plus repair job. Couldn't we just do away with these sensors, and revert to simpler times? Well, no, not exactly.

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The sensors are there to make sure that the car stays within the parameters of emissions standards. "Most of the stuff that you end up getting a 'check-engine' light for would pull it out of being a proper-emissions running car, like oxygen sensors failing," says John Broek, a Vancouver-based Porsche technician. "Camshaft sensors or activations failing mean that the camshafts aren't working properly because they're not as basic as they were in the past. Now all the cars have both intake and exhaust camshafts that are completely adjustable. Computers are adjusting them all the time."

The sensors provide information required by emissions testing programs, such as southern Ontario's Drive Clean and British Columbia's AirCare.

"Before, a car could be misfiring or running on five-and-a-half cylinders in a six-cylinder and it wouldn't matter, the owner would just say, 'Okay, one day I'll get it fixed'," says Broek. "Nowadays, they don't want it running like that, the hydrocarbons out the tailpipe are way too excessive and that affects everybody around you. It's the greenhouse effect. They want it as clean as possible to meet emissions so that's why they put all these sensors on, so you know there's something wrong."

With the increased complexity of engine systems, the sensors are also there for safety.

"If you're driving down the street and you've got a spark plug misfiring and the catalytic converter is overheating it's going to go nuclear, and possibly light the car on fire," says Broek. "Before it was just a cylinder head, a carburetor, an exhaust manifold and a muffler. If it was misfiring, it didn't matter. Nothing was running that hot that it would light the fuel up, it would just come out as hydrocarbons out the tailpipe. Well, that's not the way it goes these days: the cat converters run at such a high temperature if any fuel gets near it, it's going to light the fuel up."

The check-engine warning can be indicative of a multitude of things, from a misfire to poor fuel, a spark plug to an ignition coil, an oxygen sensor, or a catalytic converter failure.

"That's why it needs to be checked, because it could be endangering you," says Broek. "Usually there's 'yellow faults,' meaning the 'check-engine' light will come up in yellow. And then there's red, meaning a bigger problem. A lot of systems will come up in two manners, and if it's red and blinking it means you've got a problem that must be dealt with right now."

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If you're intimidated by the warning lights, dust off your owners' manual, where the various causes for illumination are outlined. If you're lucky, the check-engine light is being triggered by an ill-fitting fuel cap.

Joanne Will writes a monthly technology column.

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About the Author

Joanne Will is based in Toronto. She has been a regular contributor to The Globe and Mail since 2009. In 2014, she was a Knight-Wallace Journalism Fellow at the University of Michigan. More


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