6 common Check Engine light problems

June 14,2015
Check Engine - Service Engine Soon light

There are many possible problems that can cause the Check Engine light to come on in your car. We have analyzed thousands of repair cases in hundreds different cars. We found several problems that are common in many cars and often produce similar symptoms. They are listed below. Of course, the causes might be different for different cars. To find out the exact cause and repair the problem, you will need to have your vehicle scanned for codes and properly diagnosed. Read this article for more information and ways to save money on diagnostics and repair.

Air induction system issues

Mass air flow sensor
Mass airflow sensor. Click for larger photo

Air induction system is responsible for supplying air to your engine. Major components of the air induction system include an intake manifold, throttle body, a rubber boot that connects the manifold to the air filter box, an airflow sensor and an air filter. Often, a leak at one of the components (called vacuum leak) lets the air to enter the engine bypassing the airflow sensor. This can cause the engine to run "lean". This means that the engine is not getting enough fuel, or in other words, the air-fuel mixture has more air and less fuel than needed.

A faulty or dirty airflow sensor may also cause the same problem. Symptoms of an engine "running lean" include RPMs fluctuating up and down, stalling, rough idle, difficulty starting and lack of power. Often an engine starts, but stalls right away. Common Check Engine fault codes related to this problem are P0171 and P0174, P0101, P0102. Read more about airflow sensor.


On-plug ignition coil
On-plug ignition coil. Click for larger photo

An engine "misfires" when some of its cylinders don't work. Symptoms of a misfiring engine include shaking and lack of power. This might be more noticeable at idle. When an engine misfires, the Check Engine light flashes repeatedly or stay on solid on the dash. Sometimes misfiring happens at a cold start and goes away when the engine is revved. Often the engine misfires during rainy weather or after driving through a puddle or when accelerating from a stop.

In most cases, the misfiring is fairly easy to diagnose. One of the most common cause of misfiring in modern cars is a faulty ignition coil. However, many other problems can also cause misfiring. Read more about causes of misfiring in this article: Codes P0300 - P0308.

EVAP system leaks

EVAP purge valve
EVAP system purge valve Click for larger photo

The EVAP system prevents the gasoline vapors in your gas tank from escaping into the atmosphere. It's a sealed system and if there is a leak, the car's computer turns the Check Engine light on.

Evap leaks rarely cause any driveability symptoms. A loose gas cap is one of the examples of an EVAP system leak. Other common sources of an EVAP system leak include a purge valve and a canister vent valve. Related OBD II codes: P0446, P0455, P0441.

EGR system problems

Sticky EGR valve
Bad EGR valve

The EGR or Exhaust Gas Recirculation is one of the vehicle's emission control systems. It reduces the combustion temperature by redirecting a small amount of exhaust gases back into the engine intake. The main component of the EGR system is the EGR valve. Often, carbon deposits and soot accumulated inside the valve preventing it from opening and closing freely. This will cause the Check Engine light to come on.

Symptoms of a sticky EGR valve include stalling at idle, rough idle. Sometimes these symptoms happen after exiting the highway. In some cars, when the EGR system is clogged up, the Check Engine light may come on, but no other symptoms would be present. Common fault codes: P0400, P0401.

Oxygen sensor or air/fuel ratio sensor problems

Oxygen sensor
Oxygen sensor

An oxygen sensor is the primary sensor in the fuel injection system. Installed in the vehicle's exhaust, it provides the feedback for the engine computer on how efficiently the engine runs. A more precise air/fuel ratio sensor used in many modern cars for the same purpose is also commonly referred to as an "oxygen sensor."

Oxygen sensor problems are also common. A failed or deteriorated oxygen sensor may cause a drop in the fuel economy and the Check Engine light to come on. The vehicle may still drive fine. Common causes include a failed oxygen (air fuel ratio) sensor and shorted out sensor wires. Common fault codes: P0130, P0133, P0134, P0135, P0136.

Failed catalytic converter

Catalytic converter
Catalytic converter

A catalytic converter is the main emission control device installed in the vehicle's exhaust. It has a honeycomb-like ceramic structure inside that helps to burn any unburned fuel and reduce other harmful emissions. A failing or clogged up catalytic converter often causes the Check Engine light in many cars and trucks. When a catalytic converter becomes clogged up, an engine may start and run well at idle, but bog down when accelerated. A rattling noise coming from a catalytic converter and a smell of unburned fuel from the exhaust may indicate that the ceramic structure inside the converter has disintegrated.

In either case, the catalytic converter will need to be replaced. The most common Check Engine light codes: P0420 and P0430. The catalytic converter is typically covered by 8-year 80,000-mile Emission Warranty. If your car is still within the warranty coverage, your dealer should be able to help you

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