According to a recent study, nearly half of all cars on the road are being driven with one or more dashboard warning lights illuminated. All vehicles built since 1996 are equipped with what’s called an OBD II (onboard diagnostics) system that taps into a car’s electronic control unit on a real-time basis and illuminates either of several warning lights on the dashboard if the car is suffering a mechanical issue.
The most prevalent of these is a light that either looks like a car’s engine or spells out “Check Engine” that stays illuminated after the vehicle is started. It usually indicates there’s a problem with the emissions system, though it could mean there’s a more serious problem lurking under the hood.
When that happens the sensible course of action to take, of course, is to take the car, truck, or SUV to a trusted mechanic to have the issue checked out and repaired. The problem is the system doesn’t automatically go into detail about why the alert comes to life, and if the vehicle seems to otherwise be running fine, many drivers wind up ignoring it.
According to the vehicle repair site CarMD.com, nearly half of all cars on the road (49%) are being driven with one or more dashboard warnings illuminated, with 20% operated specifically with the Check Engine light on. This is attributed to owners putting off needed repairs because of rising parts and labor costs and extended ownership periods in what remains for many a tough economy.
The study found that vehicles from the 2007 model year are most likely to require a Check Engine-related repair. Even without serious symptoms a car or truck could suffer decreased fuel economy as great as 25% with the Check Engine light on, and at today’s gas prices, the extra cost can add up quickly. Worse, neglecting to address what might be a relatively minor problem today could lead to costlier and more complicated – and expensive – fixes down the road.
“Ignoring the Check Engine light can cause a car to fail an emissions test and can result in the need for additional repairs,” cautions David Rich, CarMD’s technical vice-president. “We encourage drivers to address all of their dashboard warning lights to help make sure their vehicle is as reliable and efficient as it can be.”
Fortunately, repair shops and many auto parts stores can plug an electronic analyzer into the vehicle’s OBD port that will display alphanumeric trouble codes to help pinpoint engine problems and other issues. More complex OBD II code readers will actually spell out the car’s mechanical issues, and can additionally provide performance information on a graphical basis, using charts, graphs and so on.
What might a motorist expect if the Check Engine light is illuminated? According to CarMD’s annual Vehicle Health Index, the number one cause during 2023 was to replace the catalytic converter (a critical emissions control component) at an average cost of $1,304. The website attributed this to the ongoing increase in the average vehicle age, as converters tend to fail most frequently on older models. This can also point to the increased frequency in owners needing to replace stolen converters that can command as much as $250 or more on the gray market for underlying precious metals that include platinum, palladium, and rhodium.
Of note, this is the first time since CarMD began tracking repair costs that a loose, damaged or missing gas cap – the least expensive Check Engine issue to correct – is not among the top five repairs. The site attributes this to greater consumer education and the fact that an increasing number of cars and trucks now come with capless fuel tanks that eliminate the component altogether.
Here are the 10 most common diagnostic-light warnings identified by the 2024 CarMD Vehicle Health Index, which is based on a study of over 15.3 million needed repairs over the past calendar year. Problems are noted along with their identifying symptoms and national average parts and repair costs; charges will vary due to local parts costs/availability for specific models and prevailing wages for auto mechanics:
1. Catalytic Converter: This critical emissions control component can fail due to a variety of factors, including age, mileage, and driving conditions. Symptoms can include a Check Engine light, decreased fuel economy, and a rotten egg smell.
2. Oxygen Sensor: This sensor monitors the amount of oxygen in the exhaust gas and helps the engine to adjust the air/fuel mixture. Symptoms can include a Check Engine light, decreased fuel economy, and rough idling.
3. Spark Plugs: These components ignite the air/fuel mixture in the engine. Symptoms can include a Check Engine light, difficulty starting the engine, and decreased fuel economy.
4. Ignition Coil: This component provides the spark that ignites the air/fuel mixture in the engine. Symptoms can include a Check Engine light, difficulty starting the engine, and decreased fuel economy.
5. Mass Air Flow Sensor: This sensor measures the amount of air entering the engine. Symptoms can include a Check Engine light, decreased fuel economy, and rough idling.
6. Evaporative Emissions Control System: This system helps to prevent fuel vapors from escaping into the atmosphere. Symptoms can include a Check Engine light and a strong fuel odor.
7. Exhaust Gas Recirculation System: This system helps to reduce emissions by recirculating exhaust gas back into the engine. Symptoms can include a Check Engine light, decreased fuel economy, and rough idling.
8. Transmission Control Module: This component controls the transmission. Symptoms can include a Check Engine light, transmission problems, and decreased fuel economy.
9. Anti-Lock Brake System Control Module: This component controls the ABS system. Symptoms can include a Check Engine light and ABS problems.
10. Airbag Control Module: This component controls the airbag system. Symptoms can include a Check Engine light and airbag problems.
