How to Troubleshoot a Check Engine Light

Below guide will teach you How to Troubleshoot a Check Engine Light . Please follow the instructions carefully.

Things You’ll Need:

  • Scan Tool

Estimated Costs:

  • DIY Costs: Est. $0.00 parts only
  • Shop Costs: Est. $102.77 parts and labor


  • Turn the vehicle on.
  • Look for the check engine light and observe it for a while.
  • Make sure that the check engine light turns on while the engine is still operating.
  • Attach the OBD scanner to the OBD output.
  • Following the instructions given in scanner’s manual, recover the diagnostic trouble code/codes. Diagnostic code usually appears to be like P0300 (Random/Multiple Cylinder Misfire Detected) which means that engine cylinders are not firing accurately. It is also important here to note that the last two numbers in the code usually refer to the defective cylinder. For instance, if the code is P0301 then the defect is in first cylinder. However, P0300 refers to a random cylinder misfire code.
  • Misfire code can be caused by a number of different reasons which are given below:
  • Faulty Spark Plug Wire(s) and/or Plug(s)
  • Faulty Coil Pack(s)
  • Faulty Fuel Injector(s)
  • Faulty Oxygen Sensor(s)
  • Faulty Catalytic Converter(s)
  • After the problem is diagnosed, you need to rectify the problem by replacing the defective component with the new one.
  • After the replacement of the defective component, you need to clear the diagnostic trouble code or codes with OBD Scanner.
  • Turn the vehicle on and again recheck the status of the check engine light.
  • Make sure that the check engine light doesn’t turn on after troubleshoot.

Further Reading

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