Check Engine Light On? Keep Driving, And It Could Cost Much More

May 2, 2011
Check Engine Light

Check Engine Light

Some people, who are otherwise paragons of fiscal responsibility, can live in a state of denial about one thing in particular: that bright orange check-engine dashboard light that's been illuminated—for weeks, or months.

Yes, the vehicle might still drive pretty much the same, and there might not be any glaring faults, but you're padding your mechanics' pockets by ignoring it—and affecting your own financial future. Many smaller issues indicated by the "check engine" light can cost as little as a few bucks to fix in the short term but could lead to thousands of dollars in repairs—as well as higher gas costs—down the line if neglected.

According to CarMD, which provides diagnostic tools and claims to be the first organization to release data on common vehicle repairs, in about 13 percent of cases where motorists brought a vehicle in for repair with the "check engine" on, a misfire was to blame—often due to neglect of scheduled maintenance and failure of relatively low-cost items like spark plugs or ignition wires.

Oxygen sensors, gas caps among most common issues

Nearly one out of every ten times the "check engine" light illuminated in 2010, the fix was to replace the oxygen sensor—a $200 repair, on average, including parts and labor. Yet with a defective oxygen sensor, a vehicle's engine-control computer will typically default to a 'safe' mix of air and fuel that not only means your engine makes less power and pollutes more but also uses up to 40 percent more fuel. That could cost hundreds of dollars a year.

Also in nearly one out of ten instances (and the most common issue over 12 years of data) the problem is even cheaper: simply, that the gas cap—an important part of new vehicles' evaporative emissions and fuel systems—wasn't sealed or functioning as it should. CarMD says that letting the light stay on and keeping the defective gas cap will release gas fumes into the environment as well as decrease fuel economy by about a half-percent; yet this repair (or inspection) averages out to less than $3 per instance.

Catalytic converter replacement increasingly rare

The third most common repair according to the data, catalytic converter replacement, costs much more. But if you take care of all the little things and don't ignore your "check engine" light you should spare yourself from ever having to do this one. Replacement can cost up to $2,000 depending on the vehicle (and averages more than $1,000), but CarMD says that failure of the cats are usually a sign that other repairs have long been neglected; today's catalytic converters are designed to last at least 150,000 and smart engine control systems have made replacement rare compared to the past.

Car repair

Car repair

Across all 1996 to 2010 vehicles, the single most diagnostic trouble code (DTC) was "System Too Lean"—often caused by a faulty Mass Air Flow Sensor, a repair that averages about $375. That issue, until it's fixed, can affect fuel economy by 10 to 25 percent and lead to more expensive repairs—making it yet another case where you're going to pay a lot more in the end by ignoring the light.

Other common failures that could be indicated by the "check engine" light include those of the exhaust gas recirculation (EGR) system, coolant thermostat, or camshaft position sensor.

Repair costs actually down in 2010

Average repair costs per vehicle are down about 16 percent from a 2006 high—thanks mostly to mechanics' better familiarization with on-board diagnostics, which in some cases can replace the old trial-and-error troubleshooting approaches.

But there are still whoppers. According to CarMD's data, major engine work remained the most expensive car repair, but the second most expensive one was to "replace hybrid inverter assembly"—more than $7,000 on some vehicles. Hybrid battery replacement also averaged more than $2,370.

Just as with nearly all aspects of vehicle ownership, take care of that issue before you become conditioned to ignore the light. Have your mechanic check it out, and pay a little now rather than a lot more later.


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