how to diagnose P0303 code on Toyota Corolla E140 (2006-2013)

Learn how to diagnose and fix P0303 cylinder 3 misfire in Toyota Corolla. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, compression tester, multimeter, noid light, vacuum gauge.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 3.
• Remove the spark plug using a socket wrench.
• Inspect the spark plug for signs of fouling or damage. If necessary, replace with a new spark plug, ensuring the gap is set according to manufacturer specifications.
• Reinstall the spark plug and torque to the manufacturer’s specifications (typically around 13 lb-ft).

3. Check and Replace Ignition Coil

• Test the ignition coil using a multimeter for proper resistance (consult service manual for specifications).
• If the coil is faulty, disconnect the wiring harness and remove the ignition coil.
• Install a new ignition coil, ensuring proper connection and seating.
• Reconnect the battery.

4. Inspect and Test Fuel Injector

• Disconnect the fuel injector connector for cylinder 3.
• Use a noid light to check for injector signal while cranking the engine. If no signal is present, further diagnose the wiring or ECM.
• If the fuel injector is faulty, remove it from the rail and replace with a new injector.
• Ensure injector O-rings are lubricated and properly seated during installation.

5. Perform Compression Test

• Remove the spark plug from cylinder 3 and install the compression tester.
• Crank the engine and record the compression reading. It should match the manufacturer’s specifications (typically around 180 psi).
• If compression is low, further investigate potential valve issues or head gasket failure.