A misfire occurs due to poor combustion of the air-fuel mixture in the engine cylinder. The engine performance highly depends on the combustion of the air-fuel mixture. When the air-fuel mixture doesn’t burn properly inside your cylinder, the cylinder starts misfiring. When any of your engine cylinders misfire, the powertrain control module (PCM) triggers a particular trouble code. When your vehicle’s engine cylinder number 3 starts misfiring, the PCM triggers the diagnostic trouble code (DTC) P0303. This article mainly explains the P0303 code meaning, causes, symptoms, and how to fix it.
P0303 Code Definition
The P0303 code stands for “Cylinder 3 misfire detected.”
What Does the P0303 Code Mean?
The diagnostic trouble code (DTC) P0303 indicates that your powertrain control module (PCM) detects that cylinder number 3 is misfiring.
A vehicle engine usually has 4, 6, or 8 cylinders. Each cylinder contains different components.
When the air and fuel mixture burns within the engine cylinder, it generates power. This output power is utilized to operate the engine. When the air-fuel mixture doesn’t burn efficiently inside the cylinder, it misfires.
The PCM continuously records the working of all engine cylinders to ensure all cylinders are firing properly. Whenever your cylinder number 3 misfires, the PCM triggers the P0303 code.
Anything from bad spark plugs to low engine compression may cause the misfires. You shouldn’t ignore misfiring because it may cause engine damage or complete failure of the engine.
Causes of P0303 Code
The P0303 engine code is triggered due to one or more of the following causes:
- Faulty crankshaft sensor
- Poor quality fuel
- Vacuum leaks
- Bad camshaft sensor
- Low fuel pressure
- Bad fuel pump
- Bad spark plugs
- Bad ignition coils
- Damaged wires or loose connections
- Faulty timing components such as bad timing belt/chain
- Faulty oil distributor
- Poor engine compression
- Blown head gasket
- Faulty fuel pressure sensor
- Faulty fuel injector
- A damaged lifter or worn camshaft lobe
- Bad air-fuel ratio sensor
- Clogged throttle body
- PCM issues
Symptoms of P0303 Code
A vehicle with the P0303 code usually produces one or more of the following symptoms:
- Engine stalling
- Limp mode
- Rough idle
- Illuminated check engine light
- Poor fuel efficiency
- Misfires
- Jerking when driving
- The gas smell from the exhaust pipe
- Poor acceleration
- A reduction in the engine power
Read More: P0304 Code Symptoms and Causes
How to diagnose the P0303 Code?
You need the following tools to diagnose or fix the P0303 code:
- Plug spanner
- OBD-II scan tool
- Screwdrivers
- New spark plugs
- Multimeter
- Fuel pressure gauge
- Compression tester
- Socket, ratchet, and extension
Follow the below-given steps to diagnose the P0303 code:
- Ensure the presence of the P0303 code by using an OBD-2. Record all stored fault codes, along with all available freeze frame data. Clear the codes and make a test drive. If the code returns, then check other parts.
- Check the ground wiring for signs of damage.
- Properly examine the connectors at the ignition coils.
- Check the wires for damage (especially cylinder 3).
- Visually inspect the spark plugs and spark plug wiring. If your car has individual packs other than the spark plug wires, first remove the coil from cylinder #3 and replace it with the coil of cylinder #4. If the misfire moved to cylinder number 4 (P0304), then you have determined that the coil pack is faulty and needs replacement. The same test can be done for the spark plugs of cylinder #3, i.e., moving spark plugs from cylinder #3 to cylinder #2, and if the misfire is now P0302, then the plugs are at fault. Replace spark plugs and spark plug wires/ignition coil packs if needed and recheck for misfires.
- Check fuel pressure. Low fuel pressure can cause intermittent misfires on multiple cylinders. When the pressure is below the specification, the engine does not receive the proper amount of fuel and will start to lean misfire.
- Check the fuel pressure sensor and fuel pump. The faulty fuel pressure sensor or fuel pump may cause low fuel pressure.
- Inspect the fuel rails for leaks.
- Check the vacuum system for a leak. You may perform a smoke test to easily find the leaks.
- Perform a compression test to check the compression pressure within cylinder number 3. Compare the output readings with the readings written on the vehicle’s service manual.
- Properly examine the engine valves for a fault.
- Check the health of your head gasket.
- After making the necessary repairs, clear the codes and perform a test drive.
Common P0303 Code Diagnostic Mistakes
- Like any other diagnosis that is done, all steps must be followed to avoid mistakes that waste time and money.
- Not inspecting all the parts
- Replacing the unnecessary parts
- Not confirming the existence of the P0303 code
- Clearing the code without first verifying the problem
- Replacing the spark plug or fuel injector without inspecting the wiring and connectors
What repairs can fix the P0303 Code?
One or more of the following repairs can fix the P0303 trouble code:
- Replacing the bad spark plugs
- Replacing the burned or damaged valve
- Repairing the fuel rail leaks
- Replacing the bad fuel injectors for cylinder number 3
- Replacing the bad fuel regulator
- Replacing the bad fuel pump
- Replacing the bad fuel pressure sensor
- Replacing the spark plug wiring or coil pack
- Adding more fuel if needed
- Replacing the bad ignition coils
- Cleaning the clogged throttle body
- Replacing the bad throttle position sensor
- Replacing the bad oxygen sensor
- Reprograming or replacing the PCM
P0303 Code Repair Cost
The repair cost of the P0303 code varies according to your vehicle model, labor cost, and the repair of the relevant part. P0303 repair requires one or more below-given repairs:
| Parts | Cost |
| Spark Plug replacement | $60 to $260 |
| Fuel pump replacement | $250 to $1,090 |
| Spark plug wiring repair | $170 to $250 |
| Ignition coil replacement | $220 to $650 |
| Fuel injector replacement | $1400 to $2000 |
How serious is the P0303 Code?
In general, DTC P0303 is considered to be quite severe in nature. This code may generate different drivability problems like poor engine performance or poor fuel economy that may make it more uncomfortable to drive. This code may also force the vehicle into limp mode. However, this code doesn’t force the driver to drive the vehicle to a safe location.
How To Prevent P0303 Code?
You need to follow the following control measures to prevent the P0303 engine code from triggering in the future:
- It is recommended to avoid lugging the engine. Lugging may put additional load on your engine and cause misfiring.
- Drive carefully
- Use good quality fuel
- Ensure regular tune-ups of your engine. A tune-up plays a vital role to improve engine performance and prevent misfires.
- Proper cleaning of your engine
- Ensure regular maintenance of your vehicle according to the manufacturer’s instructions.
FAQ Section
Can you drive with a cylinder 3 Misfire?
It is not recommended to drive with a misfire. However, you can drive with a misfire for a short time but don’t drive for a long time because misfiring may cause different issues such as engine stalling, poor acceleration, or poor fuel economy. However, if you continuously ignore the misfiring issue, it may badly damage your engine.
How much does it cost to fix a cylinder 3 Misfire?
The repair cost of the misfire varies according to the labor cost and the repair of the relevant part. The average repair cost of a misfire is from $90 to $1100. The most common causes of misfires and their average estimated cost of repairs are listed below:
- Poor fuel delivery fixing: $190 to $1,100
- Faulty spark plug wiring: $90 to $310
- Spark Plug Replacement: $60 to $260
- Fuel Pump Replacement: $250 to $1,090
- Fuel Injector replacement: $1400 to $2000
Can a bad catalytic converter cause a P0303 code?
Yes, a bad catalytic converter or a bad PCM may also trigger the P0303. However, a catalytic converter or PCM is very expensive to repair or replace.
Can low fuel pressure cause a misfire?
Yes, low fuel pressure is one of the major causes of the misfire. A bad fuel pump, fuel pressure regulator, or fuel rail leak may cause low fuel pressure.
Can I drive with P0303 Code?
Yes, you can drive with the P0303 code, but it is not recommended. This is because your vehicle computer triggers this code due to a misfire. Misfiring indicates a serious issue with your engine. The engine misfire generates different driveability issues, such as limp mode or poor acceleration. Driving with the P0303 code for an extended period of time may lead to the complete failure of the engine.