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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883


Check engine light woes

Ignoring or sticking black electrical tape over your car’s lit check engine light is not an advisable course of action.

Since computers began running and monitoring vehicle systems in the early 1980s, that yellow-orange check engine light has been a “catch-all” for warning drivers of system problems.  Today, the light keeps watch on hundreds of inputs from cars’ or trucks’ ignition, fuel and emissions systems, lighting up when the computer senses trouble.  While there theoretically could be a case of an electronic glitch causing illumination without a discernable defect or detriment to efficiency, it would be rare.

That’s why taking your vehicle to a trained, qualified technician for diagnosis when the dreaded light goes on is important.  Ignoring it will typically lead to poor running, reduced mileage and potential damage to costly components.

I found a list of the top ten “triggers” of check engine lights in a Bankrate online article.  Their listing follows, with my expanded explanation.  Also included are the average costs that car owners across the country paid for getting the fixes.

Oxygen sensor

This most-common cause of a lit light resides in a vehicle’s exhaust system.  It measures the by-product of engine combustion (exhaust) to help continually adjust the air/fuel mixture supply going into the engine.  Not replacing a faulty one may result in too-rich fuel mixtures and failure of expensive catalytic converters (third on the list).  Average cost to repair: $261

Loose or broken fuel cap

With a loose cap, the computer won’t be satisfied of a “closed loop” in the emissions system.  If you discover the problem yourself, it won’t cost anything to tighten it, and under $20 to replace it.  Paying a technician to tighten it will cost more, plus a bit of embarrassment.  Always check this first when you see a check engine light.

Catalytic converter

This is the biggie, with an average 2013 repair cost of $1154.  Converters contain precious metals (like platinum), accounting for escalating prices.  Failure is usually the result of a faulty, cheaper component in the system, making a case for quick attention to the first sighting of the light.

Spark plugs and wires

While the newest vehicles don’t even have these anymore, this “old school” repair is commonly needed on older autos.  Misfire and lack of power are common symptoms, and such a condition can again affect catalytic converters long-term.  Average repair is $361.

Mass Air Flow sensor

With an average cost of $423, this device is important in controlling fuel/air mixture.  As usual, a faulty one can “kill” a catalytic converter.

Ignition coil

Actually, newer autos have multiple coils or “coil packs.”  Average replacement is $250, and yes, not changing bad ones are detrimental to that costly converter.

Coils and spark plugs

A combined failure of conditions #4 and #6, costing an average of $420.


Low voltage in a battery can even cause the light to come on.  At an average cost of $110, they usually require replacement at an average interval of five years.

EGR valve

The Exhaust Gas Recirculation valve is a major component of the emissions system.  It’s fairly costly at an average of $352, but without a non-functioning one, you’ll get poor mileage and fail emissions tests.

Vacuum hoses

1980’s vehicles had dozens of these, whereas newer vehicles have few.  They can affect operation, efficiency and emissions.  Replacing dry, cracked hoses average $122 by a technician, but under $5 for a do-it-yourselfer.

The key to all of this is having access to a trusted and trained technician — an invaluable asset.  Simply “scanning” a system for fault codes will not always lead to a definitive diagnosis.  Multiple codes may be triggered in a “domino effect” by one failed component.  Qualified technicians have the equipment and knowledge to get to the bottom of a check engine light’s root cause.

Above all, don’t ignore the light’s warning just because your vehicle still runs “okay.”

Readers may contact Bill Love via email at