Having the “check engine” light turn on can be an unsettling experience. It could indicate a major problem that requires stopping the vehicle immediately to avoid a costly engine repair. However, the “check engine” light can also be triggered by a number of minor issues. It is this generic function of the “check engine” light that can frustrate drivers when it lights up.
It is not that uncommon for the “check engine” light to serve as notice that a part needs attention.
As long as the issue is addressed within a reasonable amount of time, the vehicle should suffer no long-term damage. The key is to ensure that no serious engine problem exists and then determine what has triggered the light. Below are the most common causes for the light to turn on, with a concern rating from 1 to 10, where higher value equals more concern.
1. Oxygen Sensor – Concern Level: 6
According to NAPA online, the most common reason for a “check engine” trouble code is an oxygen sensor. These sensors measure the ratio of unburned oxygen to fuel to determine whether the ratio is providing optimal efficiency.
If oxygen sensors are malfunctioning and sending incorrect data, fuel efficiency can be reduced by up to 40 percent. The engine may stall, hesitate when accelerating or have a rough idle. The vehicle will also produce more emissions that are harmful to the environment.
Oxygen sensors normally fail due to a build-up of residue. Oil leaks in the engine, a fuel mixture that is too rich or corrosion inhibitors found in some engine coolants can leave deposits that interfere with the accuracy of the sensors. Most auto manufacturers recommend having the oxygen sensors replaced periodically as part of a routine maintenance program.
Although most new vehicles have multiple oxygen sensors, replacing them is usually a relatively easy task. A code reader (available at most auto parts stores) can help identify which sensor is malfunctioning.
The owner’s manual that came with the vehicle should have complete details on where each sensor is located as well as the part number.
A few vehicles have sensors that are welded in place, but the majority of them are screw-in types. To replace, disconnect the wires and use a wrench to remove the old sensor. Screw in the new sensor by hand, being careful to avoid cross-threading, tighten with a wrench and reconnect the wires. If the sensors are welded in place or you are not comfortable with the process, consult a reputable repair shop.
2. Gas Cap – Concern Level: 2
The second-most common cause for a false “check engine” light is also the easiest to resolve, but it’s also one that is the most frequently overlooked. If the gas cap is damaged, loose or askew, sensors can detect that the system is not sealed properly and trigger a warning.
Remove the gas cap and make sure the cap and gasket are intact. Replace the cap and tighten it. If the light does not go off after driving a few miles, the problem could lie elsewhere, but it could still be related to the gas cap as not all damages are immediately visible. New gas caps can often be purchased for as little as $3, so replacing the cap is often advisable just to be sure that the light is not related to a more expensive issue.
Although a problem with the gas cap poses little risk to the vehicle, it increases the amount of pollutants released into the air. Because the vehicle’s performance is not affected, it can also lull the driver into a false sense of security, causing more serious problems to be ignored under the assumption that the light is merely related to the gas cap.
3. Vacuum Hose – Concern Level: 7
A vehicle’s Evaporative Emission Control System is designed to prevent the escape of gasoline vapors into the atmosphere. Faulty vacuum hoses can trigger an error code for this system, which can result in the vehicle’s failure to pass an emissions inspection.
However, the vacuum hoses are also an integral part of modern fuel injection systems. If there is a leak in a vacuum hose, the vehicle’s computer cannot accurately control the flow or pressure of the fuel. As a result, engine performance suffers, with symptoms that include rough idle, loss of power, and missing and sluggish acceleration. Mileage will decrease, and in some cases, the fuel can misfire and lead to engine damage.
A leaky vacuum hose has a variety of causes. The hose may simply wear out, becoming brittle or weak from age and allowing a leak to form. The plastic connector or gasket could also crack or fail.
The most common cause is a poor connection, such as a loose fitting.
Vacuum hoses are relatively inexpensive and are not particularly difficult to replace. Locating the leak, however, can be a problem, especially if it is a very small leak. Sometimes, it is possible to hear a hissing sound caused by air rushing into the leak. More often, finding the leaking hose requires moving the hoses individually while the engine is running to see if the idle is affected. Once the faulty hose has been identified, hold the connector, twist the old hose to remove, moisten the replacement hose and use a twisting motion to insert it into the connection.
4. Bad Spark Plugs or Ignition Coils – Concern Level: 8
A vehicle’s ignition system contains two elements — spark plugs and ignition coils — that can often trigger a “check engine” light. Spark plugs are used in internal combustion engines to ignite the fuel mixture needed for the engine to run. The vehicle’s coil is part of the electrical system that converts the low voltage from the battery into the higher voltage needed for ignition.
In addition to a warning light, a bad coil or spark plug can make the engine have a rough idle, misfire or surge. The vehicle may have a difficult start or accelerate slowly. It is possible for bad plugs to also drain the battery. Fuel consumption will be affected as well. A single defective spark plug can reduce mileage by as much as 5 percent, while a defective coil can reduce mileage by as much as 40 percent.
Even though it’s often recommended to replace spark plugs at least every 30,000 miles, lots of vehicles today have platinum tipped spark plugs that last substantially longer, up to 100,000 miles. Check what type of spark plugs your car has to know when it’s time to change them.
However, spark plugs can fail much sooner, especially if other problems are present, such as a too-rich fuel mixture. Changing spark plugs regularly is an inexpensive procedure that can prevent more costly repairs, such as damage to the catalytic converter.
5. Catalytic Converter – Concern Level: 10
A catalytic converter is an important part of a vehicle’s emission-control system. Its purpose is to convert emissions that are harmful to the environment into less-damaging compounds. If a failing catalytic converter triggers a “check engine” light, it is important to have the problem corrected as soon as possible. Replacing a catalytic converter is a costly proposition, and diagnosing a problem with it is best left to a professional.
It can have a major impact on the vehicle’s safe operation. In addition to causing the engine to misfire and reducing fuel economy, a bad catalytic converter can cause stalls while driving and it may be difficult to restart the car. The engine may respond as if it is not receiving any fuel or the car may jerk as if the engine is only receiving fuel sporadically.
The catalytic converter may fail if foul spark plugs cause it to overheat or if certain chemicals, such as those found in some fuel additives, “poison” it. It can also suffer external damage from debris striking at it with moderate force. Engine misfires and clogged exhaust systems can damage it as well.
6. Mass Air Flow Sensor – Concern Level: 7
The mass air flow sensor can trigger a “check engine” light for a variety of reasons. The problem is that the issues can range from minor annoyances to those requiring immediate repair. Because of the number of potential causes, diagnosing a defective mass air flow sensor normally requires the services of an experienced mechanic.
The mass air flow sensor reads the temperature of air flowing across it. This information is relayed to the computer, which can make adjustments to the fuel mixture and emissions systems to compensate. However, some issues might cause the sensor to transmit incorrect data. For example, a dirty air filter often causes a misreading of ambient air temperature, so drivers who frequently travel unpaved roads or in high-dust areas should pay special attention to keeping their air filters clean.
A defective mass air flow sensor can make an engine stall or idle poorly. Drivers may notice a lack of power, hesitation that can range from minor to severe or reduced fuel economy. These are also the symptoms for a number of other failures that can cause the “check engine” light to activate, complicating the diagnosis, so it’s best to consult a professional.
A “check engine” light does not always mean that it is necessary to call a tow truck or have a roadside repair performed.
One of the best ways to prevent false alarms is to follow the preventive maintenance schedule recommended by the manufacturer.
However, the “check engine” light should not be ignored as the underlying issue will worsen, potentially leaving the driver stranded or facing a large repair bill.All vehicles benefit from routine care, and it is the best way to keep the “check engine” light off.