How do I fix the P0303 engine code?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

P0303 is an error code that typically indicates that there is a problem with the cylinder 3 misfire. This means that the cylinder is not firing correctly, and as a result, the engine is not running as efficiently as it should be. There are a number of reasons why this might happen, including a problem with the spark plugs, the ignition system, or the fuel system. In some cases, it can also be caused by a leak in the exhaust system.

Users typically search for a solution by asking about:

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1. Check the spark plugs and wires

  1. Remove the spark plugs from the engine. This can be done using a spark plug socket or a wrench. Make sure the gap is at .030 inch and that the threads are clean.
  2. Check the wires for cracks, cuts, or wear. Make sure they are not twisted or kinked. If there are any problems, replace the wires.
  3. Reinstall the spark plugs and tighten the bolts to 20 foot-pounds (22 Nm).

2. Check the injectors

  1. Remove the fuel filter
  2. Pry open the injectors with a flathead screwdriver
  3. Clean the injectors using a fuel cleaner and a brush
  4. Replace the injectors if necessary

3. Check for vacuum leaks

  1. Start the engine and allow it to idle for a few minutes.
  2. Check the vacuum lines and hoses for any leaks.
  3. Check the engine vacuum port to determine if there is any vacuum loss.
  4. Repair or replace any vacuum leaks.

4. Check the EGR valve

  1. Remove the air cleaner element.
  2. Check the fuel filter for blockages.
  3. Check the EGR valve for proper function.
  4. Clean and inspect the engine parts.

Some users might also have success with the following opitons:

  1. Check the ignition coil.
  2. Check the fuel pressure.
  3. Check for a blown head gasket.
  4. Check the PCV valve.
  5. Check the compression.