How to Troubleshoot a Check Engine Light?

Start your vehicle.Locate your check engine light and monitor its status.

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Verify that the check engine light is on while the engine is running.Connect scanner to the OBD output.

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Follow the OBD Scanner's instructions to retrieve diagnostic trouble code(s).

Troubleshoot all possible symptoms that relate to the diagnostic trouble code(s).

FOR EXAMPLE READ THIS:---
Ex: P0300 – Random/Multiple Cylinder Misfire Detected
This code indicates that the vehicle's onboard computer has detected that not all of the engine's cylinders are firing properly.
The last 2 digits of the code represent the detected cylinder. In this case 00 is a random cylinder misfire code. A P0301 would be a misfire detected on cylinder 1. It will be much easier to diagnose if a specific cylinder is detected.There are numerous components that could set a misfire code. Below is a list of possible components that could be at fault:
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)

Once you have diagnosed the problem that set the check engine light on, you must now replace the faulty component(s).Once the new component(s) has been replaced, use the OBD Scanner to erase the diagnostic trouble code(s).Start your vehicle and monitor the status of the check engine light.If further diagnosing is required, these steps must be repeated until the check engine light is no longer on.