Keeping your tires inflated properly and your engine running right is critical to efficient driving. Underinflated tires can lower your fuel economy by full kilometres per litre. (Get the proper inflation pressure from the sticker on your car’s doorjamb or the owner’s manual, and not the tire’s sidewall.) Even if your car seems to be running well, that perplexing Check Engine light could represent a dead oxygen sensor or some other emissions control problem causing the vehicle to waste gas.