P0303 – OBD-II DTC

OBD-II DTC P0303 – Cylinder 2 Misfire Detected

DTC P0303 meaning

DTC P0303 indicates that the Engine Control Module (ECM) has detected a misfire in cylinder number 2. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, leading to incomplete combustion. This can result in poor engine performance, increased emissions, and potential damage to the engine if not addressed.

DTC P0303 symptoms

Common symptoms associated with DTC P0303 include:

• Rough idling or engine shaking
• Decreased engine power and acceleration
• Increased fuel consumption
• Illuminated Check Engine Light (CEL)
• Unusual engine noises, such as backfiring

DTC P0303 causes

Several factors can lead to a misfire in cylinder 2, including:

• Faulty spark plug or spark plug wire
• Defective fuel injector
• Vacuum leaks affecting air-fuel mixture
• Compression issues in the cylinder
• Faulty ignition coil
• Engine control module (ECM) issues

DTC P0303 seriousness

DTC P0303 should be taken seriously as it can lead to:

• Increased emissions, potentially failing emissions tests
• Engine damage if misfires persist
• Poor fuel economy
• Loss of power and drivability issues

How to diagnose DTC P0303

To diagnose DTC P0303, follow these steps:

1. Use an OBD-II scanner to confirm the DTC and check for any additional codes.
2. Inspect the spark plug and ignition coil for cylinder 2.
3. Check the fuel injector operation for cylinder 2.
4. Perform a compression test on cylinder 2 to assess engine health.
5. Look for vacuum leaks around the intake manifold and hoses.
6. Examine the wiring and connectors related to the ignition and fuel systems.

How to fix DTC P0303 step-by-step instructions

To fix DTC P0303, follow these steps:

1. Replace the spark plug and ignition coil for cylinder 2 if they are faulty.
2. Clean or replace the fuel injector for cylinder 2 if it is clogged or malfunctioning.
3. Repair any vacuum leaks found during the diagnosis.
4. Address any compression issues by checking the cylinder head, valves, and piston rings.
5. Clear the DTC using an OBD-II scanner and test drive the vehicle to ensure the issue is resolved.

How to erase DTC P0303

To erase DTC P0303, follow these steps:

1. Connect an OBD-II scanner to the vehicle’s diagnostic port.
2. Turn on the ignition without starting the engine.
3. Navigate to the “Erase Codes” or “Clear DTCs” option on the scanner.
4. Confirm the action to clear the codes.
5. Disconnect the scanner and start the engine to verify that the code does not reappear.

Recommended tools for OBD-II diagnostics

Explore our expert picks: The Best OBD2 Scanners for 2025

Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter

Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.