Check Engine Light Common Causes

Author: JRAutofix  Date Posted:8 January 2020 

Check Engine Light solution to quickly solve the issue with your car.

Check engine light common causes The engine check light is there to indicate the driver that something is malfunctioning with the car.

It happen in 2 stages, first stage the engine light comme on and stay on, second stage the light comme on and is flashing.


As the first stage is an early warning it's better to investigate as soon as possible.

For the 2nd stage it's a more serious problem and you should stop driving your car.


What to check to fix it:

First thing to check is whether you notice anything else wrong with the car either noise, vibration, power loss, smoke.

Next to diagnose and identify the area which is causing the issue is to connect an OBD code reader to the car computer.

The code that the scanner will give you should help you identify the faulty component in the best case or the area to further investigate.

The O2 sensor can be faulty giving an incorrect reading but it can be also due external reason as the cable could be damage or an injector leaking, exhaust gas leak before the sensor ...

To fully understand you need to make sure to read all the faulty codes given by the scanner.


The main component relating to the check engine light are:

  • The oxygen sensor which is a part that monitors the unburned oxygen from the exhaust. It helps monitor how much fuel is burned. A faulty sensor means it's not providing the right data to the computer and causes a decrease in gas mileage. Most cars have between two and four oxygen sensors and the code you get from the scanner will tell you which one needs replacing. ( Related codes: P0133 P0135 P0141)
  • The EGR valve, the EGR valve meters exhaust gases to be mixed with the intake fuel charge and this dilutes the mixture. Allowing exhaust gas to flow into the combustion chamber and reduces the amount of nitrogen oxides produced at the tail pipes.
    If the passageway from the exhaust to the intake is becoming clogged this will causes a reduction in gas mileage and increases emissions. (Related code: P0401, P0402)
  • The catalytic convertor works to reduce exhaust gases. It converts carbon monoxide and other harmful materials into harmless compounds. If your catalytic convertor is failing, you'll notice a decrease in gas mileage or your car won't go any faster when you push the gas. ( Related code: P0420 P0430)
  • The mass airflow sensor tells the car's computer to add the proper amount of fuel based on the air coming through to the engine. A faulty one can increase emissions, cause the car to stall, and decrease gas mileage. (Related code: P0100, P0101, P0102, P0103, P0104)
  • The spark plug seals the combustion chamber and provides a gab for a spark to jump across and initiates combustion in your engine. When the plugs are failing, the spark plugs misfire. You'll feel a little jolt in your car's acceleration when this happens.


The main component relating to the check engine light flashing:

  • Distribution belt 
  • Engine compression
  • Fuel 
  • Air intake/Exhaust


If not you can get the accurate code definition on: OBD trouble codes are five-character alphanumeric designations that begin with a letter followed by four numbers.

Most Common Trouble Codes
The following is the list of the 20 most common OBD II trouble codes:

  • P0420 - Catalyst System Low Efficiency
  • P0171 - Fuel Trim System Lean Bank 1
  • P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient
  • P0174 - Fuel Trim System Lean Bank 2
  • P0442 - Evaporative Emission (EVAP) System Small Leak Detected
  • P0300 - Engine Misfire Detected (random misfire)
  • P0455 - Evaporative Emission (EVAP) System Leak Detected (large)
  • P0440 - Evaporative Emission (EVAP) System
  • P0141 - Oxygen Sensor Heater (H02S) Performance Bank 1 Sensor 2
  • P0430 - Catalyst System Low Efficiency Bank 2
  • P0135 - Oxygen Sensor (HO2S) Performance Bank 1 Sensor 1
  • P0446 - EVAP Vent Solenoid Valve Control System
  • P0128- Coolant Thermostat P0301 - Cylinder 1 Misfire Detected
  • P0411 - EVAP System Control Incorrect Purge Flow
  • P0133 - Oxygen Sensor Slow Response Bank 1 Sensor 1
  • P0303 - Cylinder 3 Misfire Detected
  • P0304 - Cylinder 4 Misfire Detected
  • P0302 - Cylinder 2 Misfire Detected
  • P0325 - PCM Knock Sensor Circuit          


Complete guide to solve OBD2 codes available.


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