Why my check engine light come on when i crank the car?

The Check Engine Light (CEL) is designed to alert you to a problem with your vehicle's emission control system. When you turn the key or press the start button, the CEL should come on briefly as part of the vehicle's self-diagnostic test. If the light stays on after the engine starts or comes on while you are driving, it indicates that the vehicle's computer (ECU) has detected an issue with the emission control system.

Here are a few reasons why your Check Engine Light might come on when you crank your car:

1. Loose or Faulty Gas Cap: A loose or faulty gas cap can cause a small leak in the fuel system, which can trigger the Check Engine Light. Make sure the gas cap is tightened securely after each refuel.

2. Faulty Oxygen Sensor: The oxygen sensor measures the amount of oxygen in the exhaust gas to ensure proper fuel-air mixture for efficient combustion. A faulty oxygen sensor can lead to incorrect fuel mixture, triggering the Check Engine Light.

3. Spark Plug or Ignition Coil Issues: Worn-out spark plugs or faulty ignition coils can cause incomplete combustion, leading to increased emissions and triggering the Check Engine Light.

4. Catalytic Converter Problems: The catalytic converter helps clean the exhaust emissions before they are released into the atmosphere. If the catalytic converter is clogged or damaged, it can cause the Check Engine Light to come on.

5. Evaporative Emission Control System Leaks: Leaks in the evaporative emission control system can cause fuel vapours to escape into the atmosphere. This can trigger the Check Engine Light as the system is designed to capture and prevent the release of fuel vapours.

6. Faulty Mass Air Flow (MAF) Sensor: The MAF sensor measures the amount of air entering the engine to determine the appropriate amount of fuel needed for combustion. A faulty MAF sensor can lead to incorrect fuel-air mixture, causing the Check Engine Light to come on.

7. Exhaust Gas Recirculation (EGR) System Issues: The EGR system recirculates a portion of exhaust gas back into the engine to reduce emissions. If the EGR system is malfunctioning, it can lead to increased emissions and trigger the Check Engine Light.

If the Check Engine Light comes on while you are driving, it's important to have the vehicle diagnosed by a qualified mechanic as soon as possible to identify and address the underlying issue. Ignoring the Check Engine Light can lead to decreased fuel efficiency, increased emissions, and eventually more serious engine problems.