A misfire occurs when there is an insufficient amount of fuel burning in a cylinder. The engine performance highly depends on burning the air-fuel mixture inside the cylinder. When the air-fuel mixture doesn’t burn properly inside your cylinder, the cylinder starts misfiring. A misfire can be easily noticed by retrieving the activation code from the car’s onboard diagnostics system. The diagnostic trouble code (DTC) P0303 represents a misfiring in cylinder 3. This article mainly explains the P0303 code meaning, causes, and symptoms.
P0303 Code Definition
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) has detected that cylinder number 3 is not firing properly.
When your engine misfires, your PCM triggers the check engine light and may put the car into limp mode to avoid damage. The check engine light will remain until the code is repaired. A vehicle engine usually contains 4, 6, or 8 cylinders.
When the air-fuel mixture burns inside the cylinder, it generates power. This generated power is used to run 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 the 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
- Faulty crankshaft sensor
- Poor quality fuel
- Vacuum leaks
- Bad camshaft sensor
- Low fuel pressure
- Bad fuel pump
- Bad spark plugs
- Bad ignition coils
- Damaged wiring of the spark plug
- Engine timing off
- Faulty oil distributor
- Low engine compression
- Head gasket leaks
- Faulty fuel pressure sensor
- Faulty fuel injector
- A damaged lifter or worn camshaft lobe
- Bad air-fuel ratio sensor
- PCM issues
Symptoms of P0303 Code
- Engine stalling
- Rough idle
- Illuminated check engine light
- Limp mode
- Misfires
- Jerking when driving
- The gas smell from the exhaust pipe
- Poor fuel economy
- 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
- Screwdrivers
- Leakdown tester
- Digital Multimeter
- Compression tester
- Spark plug wires
- OBD-II scan tool
- Fuel pressure gauge
- Spark plugs
- Socket, ratchet, and extension
Follow the below-given steps to diagnose the P0303 code:
- Use an OBD-2 scan tool to check the existence of the P0303.
- 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.
- Inspect the loose engine ground wiring.
- Check for loose connectors at the ignition coils.
- Check the wiring 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.
- Perform a compression test and leak-down test to inspect if any engine mechanical problems are causing the misfire. The mechanical components (such as a bad valve spring, bad piston ring, head gasket leak, damaged valve, or worn valve guides) may cause the engine to misfire.
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 properly 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?
- Replacing the spark plugs for all cylinders
- Replacing the burned or damaged valve
- Repairing the fuel rail leaks
- Replacing the bad fuel injectors for all cylinders
- Replacing the fuel regulator
- Replacing the bad fuel pump
- Replacing the fuel pressure sensor
- Replacing the spark plug wiring or coil pack
- Adding more fuel if needed
- 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 Coils | $220 to $650 |
| Fuel injector replacement | $1400 to $2000 |
FAQ Section
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.
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.
