A free CarMD service

Save money on common check engine light repairs with this trick

Did you know that repair shops charge you markup fees on the parts used to repair your vehicle? Sometimes these fees can be 25%-50% of the cost of the part. Save money by purchasing the parts online and asking the shop to use your parts for the repair.

Update May 01, 2017: Did you know you can prevent a lot of Check Engine Light problems through proper maintenance? CarMD has a new service called CarMD Garage which helps you maintain your car, truck, SUV or van by giving you a report of what service items are due and links to where you can buy the parts and items needed to complete the service, should you choose to do it yourself.

Which one is the right part? Every repair listed has an ‘associated trouble code’. If the repair’s code matches your vehicle’s code, then CarMD is very certain the part needed is the correct repair for your vehicle.

To get your vehicle’s code, you can visit parts stores (such as Autozone – excluding Hawaii) and they’ll get it for free or you can purchase an obd2 scanner similar to this one. Just plug in the tool and you get the code in seconds.

Not sure? Retailers like Amazon will give you a full 100% refund on any orders returned within 30 days. So there’s no risk and you could save $100s.

Enter vehicle year make model below to customize the results to your vehicle

Your car’s O2 sensor measures the air-to-fuel ratio of your engine. When sensors begin to fail they report back to your vehicle’s computer that it needs more fuel or less fuel than it actually needs.

What causes it: While O2 sensors will fail eventually, premature failure can be due to neglected maintenance, such as missed oil changes.

If not repaired: In the short term, this decreases fuel economy, but if neglected can lead to expensive damage to the catalytic convertor.

Associated Trouble Codes: P0135, P0141

Your car’s catalytic converter turns pollutants and toxic gases created from the internal combustion process into less environmentally unfriendly substances.

What causes it: Catalytic converters typically fail with excess vehicle age, but can fail prematurely if a driver ignores a small problem such as a spark plug or O2 sensor failure. This can in turn cause the vehicle to misfire. A misfire is when one or more of the cylinders are not contributing to your vehicle’s power, and raw fuel may be running out of the engine into the catalytic converter. Your vehicle typically warns of a misfire with a blinking check engine light, which indicates a very severe problem.

If not repaired: A malfunctioning catalytic converter will not allow your vehicle to pass an emissions test and you’ll experience diminished fuel economy and performance in the short term. If left untreated long term, it can cause permanent harm to internal engine components, the vehicle’s fuel system and can even cause a fire.

Associated Trouble Codes: P0420, P0430

Ignition coils provide the spark that ignites the fuel and air mixture to your car’s engine. 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 one per cylinder.

What causes it: Several conditions can contribute to its failure, including faulty spark plugs, high underhood temperatures and age.

If not repaired: Ignoring a faulty ignition coil can cause starting problems, a decrease in fuel economy, engine misfires and backfires. The last two can lead to bigger and more expensive repairs if the ignition coils aren’t replaced soon, such as damage to the catalytic converters.

Associated Trouble Codes: P0304, P0303

Believe it or not, missing or damaged gas caps are among the most common reasons for the check engine light. They can cost drivers in time, money and trips to the repair shop visit.

What causes it: Forgetting to tighten your car’s gas cap after a fill-up or leaving it dangling alongside your car as you drive away from the gas station is the most common reason for gas cap-related check engine lights. Driving in high altitudes during summer months can also cause heat to build up in the gas tank because there is less air pressure and more fuel flow. A gas cap can also fail if the rubber around it gets a tiny hole or rip. And of, course, it can become stolen or left behind at the pump altogether.

If not repaired: Missing or damaged gas caps cause 147 million gallons of fuel to evaporate into the air annually. Simply tightening the cap for free or replacing it for a couple dollars usually fixes the problem, but if left unchecked can result in lower gas mileage and harm the environment.

Associated Trouble Codes: P0456, P0455, P0442, P0440

Your car’s thermostat regulates the operating temperature of the engine; 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.

What causes it: A vehicle’s thermostat can be susceptible to age, sludge and extreme temperatures. It can also rust, get stuck or fail if the coolant is not changed at recommended mileage intervals.

If not repaired: When your car’s thermostat fails it could it either cause your vehicle’s engine to run too cold, affecting performance and eventually damaging other components, such as catalytic converters. An engine running too hot can destroy internal components.

Associated Trouble Codes: P0128, P0125

The mass air flow sensor (MAF) meters the air coming into your car’s engine and determines how much fuel to inject into the engine.

What causes it: Mass air flow sensors are susceptible to dry, dusty road conditions. An easy and affordable way to keep your MAF sensor healthy is by keeping your car’s air filter clean. Air filters usually cost less than $20 to replace, while mass airflow sensors average roughly $400 in parts and labor.

If not repaired: A malfunctioning Mass airflow sensor can lead to poor performance, reduced fuel efficiency and damage to the catalytic converter.

Associated Trouble Codes: P0171, P0174

Small but mighty, spark plugs deliver little “bolts of lightning” that ignite the air/fuel mixture that drives your car’s engine.

What causes it: Common causes for spark plug failure include mechanical damage, overheating and improper installation. Cold weather can also affect spark plugs, causing droplets to form and foul the plug.

If not repaired: If your car’s spark plugs or wires are not functioning properly, the air/fuel mix will not fully ignite in the combustion chamber, leading to poor performance, lower miles-per-gallon (MPG), and if not addressed can lead to more problems, such as damaged O2 sensors, ignition coils, and even catalytic converters.

Associated Trouble Codes: P0300, P0303, P0302

Your car’s evaporative emission system (EVAP) reduces the amount of pollution that is emitted to the environment by limiting the amount of fuel vapors that get released. This system consists of valves, solenoids, vacuum hoses and other components. When the engine is running and fully warmed up, the engine computer gradually opens the purge valve to allow some fuel vapor to be moved from the charcoal canister the engine. When the amount of vapor is more or less than expected, the “check engine light” is activated.

What causes it: Purge valves can often get stuck partially open or closed due to pieces of carbon, which is a fairly simple and inexpensive fix.

If not repaired: If an EVAP purge control valve gets stuck open, it can cause a small vacuum leak, which will cause rough idling and poor acceleration. If it gets stuck closed, it can cause premature failure of the catalytic converter.

Associated Trouble Codes: P0440, P0446

A fuel injector is an electronically-actuated electromagnetic valve typically mounted on the engine’s intake manifold. Fuel Injectors provide atomized fuel into the intake manifold and into the combustion chamber (engine cylinder).

What causes it: Fuel injectors can become dirty or clogged because of many things such as extreme temperatures and poor fuel quality (cheap gasoline), or neglected maintenance.

If not repaired: Fuel injector problems may result in excessive fuel consumption and poor engine performance, if neglected, can cause physical damage to critical engine components. You might notice that your car has idling problems, lack of power or that you’re filling up your gas tank more often.

Associated Trouble Codes: P0300, P0171

EGR valves helps your car run more efficiently and control emissions. The EGR valve re-circulates a portion of the exhaust back through the combustion process thereby lowering the combustion temperature and the formation of nitrogen oxides (NOx) emissions.

What causes it: Over time, a car’s EGR valve can become clogged or stuck open/closed from the carbon deposits that come from the soot, water and oil found in exhaust gas.

If not repaired: A faulty EGR valve or blocked EGR passage can cause rough idling, engine hesitation, misfires and poor fuel economy.

Associated Trouble Codes: P0420, P0303

LP Standard Footer mailinglist B

Sign up for the free CarMD newsletter

For exclusive offers and early look at CarMD's free services and features

NoneSave money on common check engine light repairs with this trick