Whether that yellow-orange light reads, “CHECK ENGINE,” or depicts a side-view image of an engine block, when it’s illuminated on your instrument panel, take note.  The warning means your vehicle’s on-board computer has detected a fault in one of many engine control systems.

That fault not only triggers the check engine light, but generates and stores a code that can be read with an electronic scanner to help diagnose the problem.  The problem may by minor or major, but can definitely escalate if prognosis and rectification is not sought.

While lights that monitor tire pressure, charging system, oil pressure or air bags are specific, a lit check engine light is multi-symptomatic.  CarMD has compiled a statistical list representing the ten most common check-engine-light-prompted repairs performed last year across the nation.

The second most common repair, replacing catalytic converter(s), was the most costly, but also emblematic of the woes of ignoring the light.  Seldom do catalytic converters fail without help from another failed part such as spark plugs, oxygen sensor, or another less costly component affecting fuel mixture.  The likelihood of needlessly destroying catalytic converters, for example, is lessened by early diagnosis and repair.  The top ten for 2016, with average costs, follows.

1) Replace oxygen sensor(s), $258.63.  Affixed to the exhaust system, vehicles may have one or two of these.  They measure the product of combustion (exhaust) in order to control the mix of fuel and air coming into the engine.

2) Replace catalytic converter(s), $1,190.18.  Cars have one or two of these.  They can be rendered useless or even clogged when too-rich fuel mixtures occur.

3) Replace ignition coil(s) and spark plugs, $401.22.  Faulty ones cause cylinder misfire and allow unburned fuel to enter the exhaust system.

4) Inspect for loose fuel filler cap; tighten or replace, $16.88.  On many models, this simple fault can trip the light and adversely affect engine control systems.

5) Replace mass air flow sensor, $378.15.  A major component responsible for the fuel/air ratio delivered to the engine.

6) Replace ignition coil(s), $243.42.  Cars used to have only one, but now many have one coil per cylinder.  They are replaced as a set, commonly called a coil pack.

7) Replace spark plug wires, spark plugs, $341.71.  Change intervals have become very long on modern engines, but failure still causes uneven combustion and misfire.

8) Replace evaporative emissions purge control valve, $176.45.  One of the lower-priced fixes which can lead to bigger costs if ignored.

9) Replace thermostat, $225.40.  Faulty thermostats will either cause the engine to overheat or not reach full operating temperature.  Either one is detrimental to proper “closed-loop” emissions operation.

10) Replace evaporative emissions purge solenoid, 195.95.  Coupled with number 8 on the list, the solenoid actuates the emissions valve.

Modern engine control functions — fuel mixture, timing, idle speed, and more — are all computer-controlled, and the engine control module (computer) depends on accurate input from all sensors on its network.  The check engine light monitors that network, and when lit informs the operator of a fault detected within it.

When you see the light, heed its intent by seeking a diagnosis and repair ASAP.

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

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