Check engine light lit?  Ignoring it or covering it with electrical tape is not an advisable course of action. 

Since computers began running and monitoring vehicle systems in the early 1980s, the “check engine” light has been a universal driver warning of system problems.  It monitors hundreds of inputs from vehicles’ ignition, fuel and emissions systems, illuminating when the computer senses trouble.  While there can be an electronic glitch causing illumination without a discernable defect, that condition is rare.

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.

The top ten “triggers” of check engine lights are shown below, with expanded explanations and associated costs of indicated repairs.

• 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 repair cost:  $250.

• Loose or broken fuel cap

With a loose cap, the emissions system won’t reach a “closed loop” in the computer.  If you discover the problem yourself, it won’t cost anything to tighten it, and under $20 to replace it.  Always check this first when you see a check engine light.

• Catalytic converter

This is the “biggie,” with an average repair cost over $1000.  Converters contain precious metals (like platinum), accounting for escalating prices.  Failure is usually the result of a faulty or cheaper component in the system, making a case for quick attention to the first sighting of the light.

• Mass Air Flow sensor

Having an average cost of $400, this device also controls fuel/air mixture, and 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, should be replaced in sets, and yes, not changing bad ones can be detrimental to that costly converter.

• Battery

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 over $350, but a non-functioning one will cause poor mileage and failed 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 $100 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. 

There are numerous other sensors and less frequent causes behind illuminated check engine lights, and qualified diagnosis is the only proper course of action for remedy.  Above all, don’t ignore the light’s warning just because your vehicle still runs “okay.”

Readers may contact Bill Love via e-mail at precisiondriving@spokesman.com.

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