Do You Know the Top 10 Causes of a Check Engine Light?

According to CarMD's 2021 Vehicle Health Index (the most comprehensive database of check-engine light related problems), the average repair cost for check-engine light related repair in 2020 was $378.77—a fairly significant chunk of change. If the dreaded check engine light should pop up on your dashboard, take a look at some of the most common issues that could require resolution.

Catalytic converters are part of a vehicle’s emissions system, and work to reduce pollutants and waste hazards like carbon dioxide through a redox reaction. Most catalytic converters can last for a vehicle’s entire working lifespan, but unrepaired problems such as faulty spark plugs can cause them to fail. Repairs can be quite costly, so it’s best to follow your vehicle manufacturer’s recommended service schedule.

AVERAGE REPAIR COST: $1,383

Oxygen sensor replacement is second on the list of most common check engine light repairs, particularly in vehicles which are over twenty years old. The sensor itself operates as part of the exhaust system, and detects oxygen in the exhaust that has not combusted. Most oxygen sensors need replacement after around 60,000 miles of use.

AVERAGE REPAIR COST: $243

Ignition coil and spark plug replacement are the most common check engine light repairs for vehicles around ten years old. The spark plugs are a vital part of the ignition process, and use electrical charge from the coil to ignite the air/fuel mixture within the cylinders. Misfiring, rough idling, and decreased fuel economy are some of the signs that your spark plugs may need to be replaced.

AVERAGE REPAIR COST: $389

A mass air flow (MAF) sensor helps maintain the proper air-to-fuel ratio inside the ignition chamber. Sensor failure is fairly common, and is typically indicated by severe decreases in engine performance—including stalls, hesitations, and difficult starts. It's not uncommon for MAF sensors to be contaminated with silicone from the factory.

K&N® has done extensive research on the relationship between MAF sensors and air filter performance, which can be viewed here.

AVERAGE REPAIR COST: $336

This one might be cause for a chuckle or two, but a loose or faulty fuel cap can—and often does—cause a check engine light to appear. Thankfully, it’s usually a quick and inexpensive fix.

AVERAGE REPAIR COST: $25

If you only need to replace the ignition coil—not in conjunction with the spark plugs—the repair is a bit less expensive.

AVERAGE REPAIR COST: $215

The evaporative emissions purge (EVAP) control valve is electrically operated, and prevents fuel vapors from escaping into the atmosphere (reducing dangerous emissions). Issues can arise if the valve gets stuck either open or closed. Along with a check engine light, decreased gas mileage is one indicator that the EVAP valve is not operating as it should.

AVERAGE REPAIR COST: $142

The fuel injector processes signals from your vehicle’s ECU. There is one injector for each cylinder, and the ECU instructs the injectors to spray gasoline from the injectors into the combustion chambers—which results in ignition. Fuel injectors can become clogged or sticky, particularly in vehicles that sit at idle for long periods. You may notice reduced gas mileage if one of your fuel injectors begins to malfunction. If the valve becomes stuck closed, fuel delivery can completely fail; if it’s stuck open, it may leak.

A good quality fuel filter can help protect fuel injectors from clogging and sticking. K&N fuel filters are durable and efficient, and help provide clean, consistently high flow to your engine. Look for yours here.

AVERAGE REPAIR COST: $448

A vehicle thermostat measures engine temperature (the normal temperature range is between 195-220 degrees Fahrenheit). To regulate coolant flow between the radiator and the engine, a valve opens or closes. If the thermostat malfunctions, you may observe that the vehicle overheats quickly, or that the gauge on the dashboard shows a much lower temperature reading than normal. This repair isn’t one to avoid—running an engine too hot can result in serious damage.

AVERAGE REPAIR COST: $236

Replacing the solenoid alone typically costs around $151.33.

AVERAGE REPAIR COST: $149

There are many other issues that can cause a check engine light to appear, and many of them are relatively inexpensive fixes, including loose fuel caps, A/C compressor clutch relays, EEC fuses, dirty ground wires, and more.

While thankfully not in the top 10 list, the most expensive check engine light related repair is engine replacement—clocking in at a whopping $7,050 on average. Regular vehicle maintenance—including regular oil changes and air filter services—can help prevent premature engine wear-and-tear, and can potentially save you thousands down the road.

For over fifty years, K&N has been manufacturing top-quality protection parts to help keep millions of vehicles on the road. Check out K&N performance products to help keep your engine running smoothly by installing premium K&N filtration products.