Home / Car Symptoms / Why Is My Check Engine Light On? (9 Common Problems & Cost)

Why Is My Check Engine Light On? (9 Common Problems & Cost)


All new cars since the ’70s have had computers in them to help owners enjoy their cars and meet increasing emission standards. They run everything from the car infotainment system to controlling the amount of gas vapor that is recirculated into the system.

Even lawn mowers now have computers installed to help meet CARB emissions standards for small engines. A code reader can be purchased at an auto parts store which can assist in answering your question: Why is my check engine light on?

There are many reasons a code can be generated, and many consumers will turn to a repair estimator to help them figure out what they need to do. Car owners should take their car into a mechanic for repair rather than risk damage to the engine and other expensive components.

This post covers many of the reasons that your car’s computer will generate a code and possibly turn on the check engine light.

9 Common Check Engine Light Problems To Know

My vehicle dashboard engine lightThere are many reasons the check engine light comes on. Some are easy to repair, while others may require further assessment by a mechanic. If your car’s engine light is flashing, this usually indicates a more severe problem.

Car owners should have this situation addressed quickly to avoid damage to your car’s engine, and it can also be something simple like getting oil changes.

Loose Gas Cap on The Gas Tank

Your gas cap is part of the EVAP Evaporative Emission Control System. A loose gas cap will allow gasoline vapors to escape into the environment and trigger the engine light warning. If there are no other noticeable problems with your car’s engine, tighten the gas cap.

Need New Spark Plugs and Wires

Spark plugs and wires should be replaced every 60,000 to 80,000 miles. Warn plugs and wires can cause your engine to misfire or run roughly. There may also be a loss of power, and acceleration will not be as usual. Your engine light may turn on or even beginning to flash.

Evaporative Emissions Purge Control Valve

The evaporative emissions purge control valve is part of the EVAP system and controls the number of fuel vapors that are released to the engine. On occasion, the valve will stick or not open fully, causing the engine to be difficult to start or to run roughly just after starting. These situations will cause the engine light to turn on.

Inspect Catalytic Converter

A check engine light soon can be turned on by a bad catalytic converter. If your vehicle’s fuel efficiency begins to drop suddenly, or will not accelerate or even refuse to start, you may have a bad catalytic converter. Have it checked by a mechanic and replaced if needed.

Thermostat Replacement

If your check engine light comes on and your car is overheating even after operating for fifteen to twenty minutes, you may need to have a thermostat replacement. Avoid allowing your car’s engine to overheat, since overheating can cause catastrophic damage to your engine. Fluctuating temperatures and coolant leaks around the thermostat housing are also indications of a failed thermostat.

Replace Oxygen Sensors

A bad oxygen sensor or “O2 sensor” will send incorrect readings to the car’s computer, causing the computer to make adjustments to fuel levels and air intake. Your vehicle may run less efficiently, hard starting, and even jerking while applying steady pressure to the gas peddle. Engine codes will report sensor needs replacing.

Check Mass Airflow Sensor or “MAF sensor”

The MAF Sensor measures the amount of air coming through the air filter and entering the engine. Your car’s computer uses this information to mix the correct amount of fuel and air in the fuel system, as well as recirculated gases to meet your power needs. If the sensor becomes damaged or contaminated by foreign material, the computer may not start the motor, reduced power levels result, slow acceleration and also turn on the check engine light.

Ignition Coils Problem

The ignition coil converts the car’s twelve-volt system into thousands of volts to create a spark across the spark plug gap. Faulty coils can cause the motor to misfire, the engine to run roughly and loss of power when you need to accelerate. Any of these conditions can cause poor engine performance.

Make sure the EVAP Control Solenoid is Working

The EVAP Control Solenoid is operated electrically and controlled by the car’s computer. Vapors from your car’s fuel tank are fed back to your engine after the engine has warmed up and is running at regular speed. Failure of the solenoid to operate will turn on the check engine light, low gas mileage, and potentially poor stating and a rough idle.

Read this post to know exactly when your replace your car battery.

Why Shouldn’t Car Owners Ignore Check Engine lights?

Drivers should never ignore their cars engine light. It may indicate problems in several areas. A steady light usually means there is no emergency. However, a blinking light suggests something more serious. Your car’s computer will make adjustments to attempt to deal with whatever problem there is.

Serious issues can cause unburned fuel to be passed through to the catalytic converter causing more damage. Your car engine may be misfiring or running roughly, a further indication that there are problems with your car engine. These situations should be referred to a mechanic quickly for repair and skip to content research.

What is the Onboard Diagnostic System?

The onboard diagnostic system (OBD II) or your car’s computer continuously monitors all of your cars engine performance and makes adjustments to engine speed, fuel mixture, and ignition timing. Computers have been used in vehicles since the 1980s and are becoming more sophisticated and control/monitor more and more of the operation of our car.

When the diagnostic system cannot make adjustments to compensate for issues, it cannot correct, and the system turns on the engine check light or service engine soon light. The system also will save a trouble code which can be read with an electronic scan tool. This code will indicate the source of the problem such as a loose gas cap, a sensor not working, or a misfiring engine. OBD II quickly recognizes when there is an issue with the O2 sensor, catalytic convertors, spark plug wires or timing belt.

How Does the Emission Systems Work

Emissions systems are designed to minimize the number of pollutants from your Toyota Corolla or any car brand. Typically, we think of the gases that are coming out of our car’s exhaust pipe. These systems include catalytic converters, exhaust gas recirculation systems, and evaporative control systems.

The catalytic converter reduces three harmful gases that are part of a car’s exhaust. They are carbon monoxide (poisonous), nitrogen oxides (causes smog and acid rain) and hydrocarbons (causes smog). Exhaust gas recirculation systems recirculate exhaust gases into the air intake systems to reduce the amount of nitrogen that your vehicle produces.

Evaporative control systems reduce the number of gasoline vapors that escape into the air. Gasoline evaporates even at moderate temperatures and can escape through your gas cap if it is not secure. Vapors are collected in a charcoal canister and recirculated into the engine for combustion once the car is operated again usually in non-idling situations.

Common Reasons And Why Use a Mechanic

The check engine light (CI) is the entire of an older automotive design. It is attached to your car’s on board diagnostic system. This system is manufactured around a computer that screens and directs a few features of your vehicle’s operation.

For instance, the computer watches your engine’s RPMs, the air-fuel blend inside of the individual cylinders, and its ignition timing. It might likewise control the shifting of your transmission, contingent upon your vehicle’s make and model.

At the point when a problem happens, the onboard diagnostic system will endeavor to over-right it. If it can’t do as such, it will trigger the check engine light. At whatever point the computer sets off the light, it will create a trouble code.

This code offers the mechanic some assistance with determining what is creating the problem. For instance, a coming up short oxygen sensor will produce a different code than a discharge failure.

Your mechanic will have entry to an uncommon diagnostic device that can “pull” the code from the computer. You can likewise buy a comparative tool at numerous auto supply stores.

Automakers make the trouble codes to make it less demanding for specialists to discover and resolve problems. It can be a significant issue, like replacing the mass airflow sensor or spark plug wires.

It’s worth noticing that each automaker designs their on board diagnostic system a little differently. That implies the computer in one kind of vehicle may set off codes for different occasions than another vehicle’s equipment.

There is a significant amount of overlap. For instance, all automakers have designed their computers to identify most sorts of power strain issues.

The Most Effective Method to Respond

What would it be advisable to do if you see the common check engine light illuminated on your dash? The worst thing you can do is ignore it. The first thing you need to do is check if you have a loose gas cap on the fuel tank.

If this is not the case, then you should get your fuel system, and engine checked. Plenty of issues begin little and exacerbate with time. At the point when your engine is included, this can prompt extensive – and costly – repairs.

Having the check engine light go ahead can be a shocking thing. Having the engine light enter general, for the most part, prompts some terrible feelings.

Luckily, because the check engine light is on does not generally imply that you have to spend a good chunk of cash on repairs. Sometimes, having the check engine light go ahead is not a major ordeal by any stretch of the imagination.

There’s rarely a need to pull over quickly when you see the cars check engine light. However, if it goes ahead, abstain from letting an excessive amount of time go before having a mechanic pull the trouble code.

Drive to a repair shop and request that an expert get the code at the earliest opportunity. At that point, once you have figured out whether the issue is not kidding, you can choose whether you can put off the critical repairs.

Minor Problem

If you are lucky, your check engine light is just because your gas cap is not on sufficiently tight. This frequently happens, because sometimes the inside computer in your car can’t differentiate one problem from another and alarm you to the differences.

Rather than having dozens of lights to tell you when each seemingly insignificant detail goes on, commonly your car cautions you to minimal problems by turning the check engine light on.

If you think this is the case, pull over and tighten your gas cap. It may take a couple of trips for the cars to check engine light to reset itself. However, it is undoubtedly worth an attempt.

If you have attempted that, yet it didn’t appear to affect your check engine light, check out your dashboard to check whether there are some other warning lights on.

Check your gauges for an indication of an overheating issue or a low oil pressure problem. If you find that one of the indicators is off, pull over when it is sheltered too, as running your car with little oil or when it is overheating can prompt much more severe issues down the road.

One other reason that your check engine light may be on, other than the best case scenario of a free gas cap, is that you are pushing your car too hard for the engine to keep up.

If you are towing something, for instance, and your car is attempting to get enough power to the engine, intermittently the check engine light will go ahead. In this occurrence, you could quit towing the load or have a go at going slower.

Tips When The Engine Light Comes On

When you see the cars check engine light go ahead, attempt to identify different signs that suggest a conceivably significant problem. For instance, a low oil level ought to trigger a dedicated flash, yet might likewise set off the CI light.

Since insufficient oil can make your engine overheat, you ought to pull over until you have an opportunity to replenish it. If you’re driving a Toyota Camry and subscribe to an emergency service, call a representative when you see the check engine light.

The representative can remotely pull the trouble code and decide the problem. The motivation behind your car’s check engine light coming on is to notify you of any issues that should be resolved.

If you see it illuminated on your dash, have the underlying problem identified and fixed as quickly as time permits. It’s not a splendid thought to share in the mystery and begin supplanting parts that will wind up being an enormous waste of your time and money.

The last and best plausibility is to get your Toyota Corolla into a dependable repair focus with trained and authorized professionals who have the privilege diagnostic instruments to discover accurately what is happening with your automobile.

This is the best method to get the issue sorted fast and carefully. Try not to waste time, don’t ignore it, and don’t figure. If your engine light comes on, get your auto to a qualified pro or an auto parts store.


The check engine light indicates potential problems with your vehicle. Some are easy to correct like a loose gas cap, while others require assessment by a mechanic.

Your car’s computer will generate codes in addition to turning on the check engine light. A mechanic using a code reader can quickly pinpoint the cause of the problem and make the appropriate auto repair.

Ignoring the warning and not having your car checked can cause expensive components to be damaged, increasing your repair bill substantially. At the very least, your vehicle is probably burning more fuel and emitting more pollution. These increased emissions are harmful to the environment.

The best approach to honestly figure out what isn’t right with your Toyota Camry or any car brand is to take it to a mechanic, who will attach it to an exceptional computer tool that will read the problem code your car is emitting.

It may cost $75 to have this test run. However, the significant serenity that it can offer you to realize that the warning is not genuine may well be worth the cash.

The computer will be able to identify if you need new spark plug wires, timing belt, O2 Sensor, or catalytic convertors replacement. These are common reasons that will turn your car engine light on, even if your gas cap is loose.

While you are at the car care center, check for any scratches in the exterior paint or see if you need a new car battery pack. Also, ask if they provide oil changes, and fresh air filter included with the service. If your car has carbon monoxide coming out of the exhaust, ask for emission tests to be done.

Tip: Avoid starting your car on your garage and leaving it on for your home security.

Last Updated on: November 3, 2022

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