Most common repairs, how much they cost and how price varies across U.S.

What are the most common repairs when the check engine light comes on? What’s the average cost to fix them? Do they vary by region? How does vehicle age impact repairs? Find these answers and more.

Irvine, Calif.—Since 1996, every car, light truck, SUV, minivan and hybrid sold in the U.S. has been required to have an on-board diagnostic (OBDII) system. It monitors roughly 80% of a vehicle’s systems to trigger the check engine light and alert drivers about issues related to emissions, fuel economy, drivability and cost of ownership.

Published annually since 2011, the CarMD Vehicle Health Index is an industry report to provide consumers and the automotive aftermarket with year-over-year check engine light repair insight. The index can assist repair professionals in determining the type of parts most likely needed when a car rolls into the service bay.

Here are the highlights from this year’s index, released this week.

2021 — 10 Most Common Check Engine Vehicle Repairs in the U.S.

For the third consecutive year, “replace catalytic converter” was the most common check engine repair. Catalytic converters are costly parts that don’t often fail unless maintenance or other minor and more affordable repairs such as replacing an O2 sensor are ignored too long, or the vehicle is up there in age. This can be partially explained by the upward trend in average vehicle age to a record 12.1 years in 2021. As people keep their vehicles longer, the aftermarket will need to adjust parts forecasts and car owners will need to budget for more expensive repairs.

(10 most common vehicle repairs are based on 17,312,496 repairs recommended in calendar year 2021 on 1996-2021 model year vehicles. This data applies to > 85% of cars, light trucks, minivans, SUVs and hybrids on the road in the U.S. – foreign and domestic. Source: CarMD.com Corp.)

1. Replace Catalytic Converter

The most diagnosed, “replace catalytic converter(s),” accounted for 5.78% of repairs in 2021. A catalytic converter usually won’t fail unless a related root cause – such as a faulty spark plug – is ignored for too long. As consumers hold on to their cars longer with the average vehicle age at 12 years, vehicles will outlast parts like catalytic converters.

Symptoms

Failing catalytic converters may cause the vehicle to experience reduced acceleration, sluggish engine performance, dark exhaust smoke and heat under the engine.

Repair Cost

The average cost to replace a catalytic converter in 2021 was $1,356 because they contain precious metals. No wonder catalytic converter thefts have been in the news.

2. Replace Oxygen Sensor

The 2nd most common repair was “replace oxygen sensor(s),” totaling 5.58% of CEL repairs.

Symptoms

O2 sensors can fail prematurely due to lack of maintenance like neglecting oil changes. Many drivers ignore the O2 sensor because their car often seems like it’s driving fine, but it’s reducing your fuel economy and slowly doing more damage to your car.

Repair Cost

The average cost to replace an O2 sensor in 2021 was $243.

3. Replace Ignition Coil(s) and Spark Plug(s)

The 3rd most common repair was “replace ignition coil(s) and spark plug(s),” accounting for 4.92% of repairs. This is an example of how ignoring a smaller problem like a spark plug can snowball into the need for more than one repair, adding ignition coil-related costs to the total repair bill.

Symptoms

Spark plugs and ignition coils work together to help the engine start and keep running. Faulty spark plugs can trigger ignition coil failure, which is why they are often replaced simultaneously. Symptoms include slow acceleration, loss of power, poor fuel economy, engine misfires and trouble starting the car.

Repair Cost

The average cost to replace ignition coil(s) and spark plug(s) in 2021 was $387.

4. Replace Mass Air Flow Sensor

The 4th most common repair in 2021 was “replace Mass Air Flow (MAF) Sensor” (4.53% of repairs).

Symptoms

The MAF sensor meters the air coming into a car’s engine and determining how much fuel to inject into the engine. Some of the symptoms are stalling and hesitation during acceleration. When malfunctioning, it can lower fuel economy by as much as 25%.

Repair Cost

The average cost to replace a MAF sensor in 2021 was $319.

5. Tighten or Replace Fuel Cap

The 5th most common repair was “tighten or replace fuel cap,” comprising 4.28% of repairs in 2021.

Symptoms

Missing or damaged gas caps can cost time and money, triggering the check engine light and a repair shop visit. If left unchecked, a gas cap problem can reduce fuel economy and harm the environment.

Repair Cost

The average cost to replace a gas cap in 2021 was $25. Tightening it is free.

6. Replace Ignition Coil(s)

The 6th most common CEL repair in 2021 was “replace Ignition Coil(s),” comprising 3.76% of repairs.

Symptoms

Ignition coils help the engine start and keep running. They take the battery’s 12-volt current and step it up to ignite the spark plugs. Your car may have only one ignition coil, or as many as it has cylinders. Symptoms may include rough idling – often at low speeds – or trouble starting the car, high under hood temperatures and age. A driver should pay attention to possible symptoms surrounding engine coil failure as it will soon affect other vehicle systems, such as the costly catalytic converter, and can leave them stranded by the roadside.

Repair Cost

The average cost to replace ignition coil(s) in 2021 was $214.

7. Replace Fuel Injector(s)

The 7th most common repair in 2021 (2.55%) was “replace fuel injector(s),” up from the 8th most frequently-recommended fix last year.

Symptoms

Fuel injectors help make sure the car’s fuel comes out as a fine mist so it can mix with the air passing into the cylinder. Some vehicles have more than one fuel injector, which is called muti-point fuel injection. A failing fuel injector can cause engine performance issues, poor idling, engine misfires and reduced fuel economy.

Repair Cost

The average cost to replace fuel injector(s) in 2021 was $420.

8. Replace Evaporative Emissions (EVAP) Purge Control Valve

The 8th most common check engine-related repair in 2021 was “replace evaporative emissions (EVAP) purge control valve” (2.47% of needed repairs).

Symptoms

This valve is part of the car’s EVAP system, which prevents fuel tank vapors from escaping into the atmosphere. When the engine is warmed up, its computer opens the purge valve to allow fuel vapor to be moved from the charcoal canister to be burned in the engine. If the purge flow is less or more than expected, the car may idle roughly. Since many of the most common problems share similar symptoms, it is important to diagnose check engine light issues.

Repair Cost

The average cost to replace an EVAP purge control valve in 2021 is $141.

9. Replace Thermostat

The 9th most common repair in 2021 was “replace thermostat” (2.21%).

Symptoms

The car’s thermostat regulates the engine coolant temperature to warm and cool to ideal “operating temperature.” It opens and closes as needed to regulate temperature. When a thermostat fails, it often gets stuck open. If the vehicle’s computer doesn’t see the engine coolant temperature rise to “operating temperature” within a fixed amount of time, it will set the check engine light and overheat. A vehicle’s thermostat can rust and fail if the coolant is not changed at recommended mileage intervals, or the vehicle is subjected to extreme temperatures.

Repair Cost

The average cost to replace a thermostat in 2021 was $235.

10. Replace Evaporative Emissions (EVAP) Purge Solenoid

Rounding out the top 10 of most common repair is “replace evaporative emissions (EVAP) purge solenoid.” It accounted for 1.92% of recommended repairs.

Symptoms

Your car’s EVAP purge solenoid helps control how much fuel vapor escapes into the atmosphere from your car. The purge solenoid is controlled by the engine control module or powertrain control module. It operates on a duty cycle and could be left partially open. A bad EVAP purge solenoid will also cause rough idling and difficulty starting the car. Similar to the no. 8 ranked repair, the EVAP purge solenoid is found on older vehicles, while the EVAP purge control valve is terminology for parts used on newer model vehicles.

Repair Cost

The average cost to replace an EVAP purge solenoid in 2021 was $147.

How Does Age Affect Frequency and Type of Repairs?

At what age are vehicles most likely to experience a check engine light problem? Is the model year (MY) vehicle you drive likely to need a repair soon? CarMD found that MY 2007 vehicles were most likely to need a check engine light-related repair in the past year, with brand new (still under warranty) 2021 cars and trucks least likely to have an issue with MY 2005-2008 cars and trucks most likely to need a costly catalytic converter.

Percentage of Check Engine Light Repairs in Calendar Year 2021 by MY

2009-2021 — U.S. Average CEL Car Repair Cost Trends

In 2021 car repair costs were up 3.6% overall, comprised of $143.35 in labor costs and $249.22 in parts costs, totaling just under $393 on average. Labor costs were down half a percent, which CarMD partially attributes to more DIYers doing their own repairs and competition among auto repair shops. As projected by CarMD last year, parts costs were up 6%. Factors that played a role in this parts cost increase include supply chain issues coupled with an uptick in more expensive car parts failing as consumers hold onto their cars and trucks longer than ever before due to lack of new car inventory.

Regional Repair Costs

Repair costs were up in all four regions of the U.S. in calendar year 2021, with drivers in the South and Northeast seeing the biggest spike – both up 3.7%.

• Vehicle owners in the West paid the most for check engine-related car repairs ($406). Vehicle owners in the Midwest paid the least on average ($366).

• The region with the highest average labor expense for a check engine light repair was the South ($144.82). The region with the lowest average labor expense for a check engine light repair was the Northeast ($136.68). This is not hourly rate, but the average amount of labor time charged for a related repair. This can be impacted by regional labor rates, what an individual shop charges to do the repair, and how difficult the repairs are.

2021 Average Cost to Repair a Check Engine Light Issue — By Region