P0303 Engine Code [Causes and Fixes]

The causes of the P0303 engine code in Toyota vehicles include low compression, ignition system issues, fuel system problems, air intake or intake manifold leaks, damaged spark plug wires, bad camshaft sensors, broken cylinder heads, bad crankshaft sensors, and a poor PCV valve.

The solution for all the causes is diagnosing the exact cause by scanning with an OBD-II scanner and then troubleshooting the cause yourself or with the help of a professional mechanic.

The P0303 engine code is a misfire code, which means the 3rd cylinder is misfiring. I have discussed all the possible causes of the P0303 code and how to solve them.

What Does P0303 Engine Code Mean?

The P0303 engine code means a misfire in the 3rd cylinder of your vehicle’s engine. If you see the P0303 code in the scanner, it means there is a problem in the combustion chamber of the 3rd cylinder in the engine.

It occurs when the 3rd cylinder has a problem with the fuel or ignition system or the air-fuel mixture is not compressed well. You may also see the code if there is a leak in the engine’s air intake or intake manifold. There are some minor causes for the code, too.

Symptoms of P0303 Engine Code in Toyota

4 symptoms of the P0303 code in Toyota vehicles:

  1. You may feel trembling, or the vehicle may halt when it runs slowly.
  2. The ‘Check Engine Light’ is on.
  3. Your car may lose power while accelerating or be hard to start.
  4. You will see a change in the color of the exhaust gases.

P0303 Engine Code in Toyota [4 Causes and Their Solutions]

There are 4 major causes for the P0303 engine code:

  1. Low compression
  2. Ignition system issue
  3. Fuel system problem
  4. Air intake leak or Intake manifold leak

Let us discuss these 4 causes and their solutions.

Cause 1: Low Compression

If the piston or valve in the 3rd cylinder is damaged or the air-fuel ratio is poorly compressed, the cylinder will misfire.


Replacement is the most suitable option when you find damaged valves or pistons. Another possible solution is routinely cleaning the carbon on the valves. Don’t keep the valve spacing too tight.

Cause 2: Ignition System Issue

The cylinder misfires if there is any space or gap in the spark plug. Usually, the gap is between 0.6 and 1.8 mm (0.024–0.071 inch). And if there is any oil or water on the ignition coil, it also leads to misfire issues.


First, check the spark plug to see if there is any gap or damage. Secondly, clean any water or oil on the ignition coil. Ensure proper electrical connections in cylinder 3. If you find a defective spark plug, coil, or wire, replace the parts to solve the misfire.

Cause 3: Fuel System Problem

A dirty fuel injector and low fuel pressure cause cylinder 3 to misfire.


Clean the fuel injector well or change it if damaged. Examine the fuel filter and fuel pump to avoid low fuel pressure.

Cause 4: Air Intake Leak or Intake Manifold Leak

Air intake leaks deliver no-filter air into the engine. An intake manifold leak delivers rich and contaminated air into the engine. Both matters can cause cylinder 3 to misfire.


Check the air intake and the intake manifold hoses or pipes for any damage or holes. Use a smoke machine if the leak is invisible.

Other Possible Causes

There may be 5 other possible causes, including:

  1. Damaged spark plug wire
  2. Bad camshaft sensor
  3. Broken cylinder head
  4. Bad crankshaft sensor
  5. Poor PCV valve


Examine all the causes carefully if you notice any damage to the parts, repair or replace them as needed.

How to Diagnose and Troubleshoot P0303 in Toyota

Diagnose the P0303 engine code with an OBD-II scanner tool. Inspect all common symptoms of the P0303 code to troubleshoot the issue. I recommend hiring a professional mechanic to solve the problems.

How Engine Code P0303 Affects the Performance of the Car

If your vehicle’s engine has the P0303 code, it may decrease your vehicle’s power. You may feel trembling, and sometimes the vehicle may halt while the engine is slow.

If the 3rd cylinder misfires, unused fuel may enter the exhaust manifold. And thus, misfiring can damage the whole engine.

How to Prevent P0303 Engine Code in the Future

To prevent the P0303 code in the future, follow these 7 steps:

  1. Observe your fuel injectors, air intake system, and intake manifold regularly. Do compression tests frequently.
  2. Check spark plugs every 45,000 miles.
  3. Always use high-quality gasoline.
  4. Don’t carry a heavy load.
  5. Change engine oil in a routine way.
  6. Drive smoothly.
  7. Regularly service your car.

How Much Does It Cost to Fix P0303 Engine Code?

First, you must hire a mechanic to diagnose, who will charge you between $100 and $150 for an hour of labor. Secondly, you will buy the necessary parts for $50 to $200.

Finally, you will hire a laborer who will charge from $100 to $300. So, you will spend $150 to $500 in total.

Leave a Comment