how to diagnose misfire in Toyota Corolla E140 (2006-2013) with P0301 code

Solution

1. Preparation

• Gather tools and parts for the repair.
• Disconnect the negative battery terminal to ensure safety while working on the vehicle.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 1.
• Extract the spark plug using a spark plug socket and ratchet.
• Inspect the spark plug for wear or fouling; replace if necessary.
• Install a new spark plug, ensuring it is gapped correctly (typically 0.044 inches for a Corolla).
• Reinstall the ignition coil securely.

3. Inspect and Replace Ignition Coil

• If the spark plug is in good condition, test the ignition coil using an ohmmeter to check for proper resistance values.
• If the ignition coil is faulty, remove it from the engine.
• Install a new ignition coil for cylinder 1.
• Reconnect the electrical connector to the coil.

4. Test and Replace Fuel Injector

• Disconnect the fuel injector connector for cylinder 1.
• Use a multimeter to check the injector's resistance; compare it to specifications (usually around 12-16 ohms).
• If the injector is faulty, remove it and clean or replace it as necessary.
• Reconnect the fuel injector and ensure it is seated properly.

5. Verify Compression

• If misfire persists, perform a compression test on cylinder 1.
• If compression is low, further diagnostic work is required to assess piston rings, valves, or head gasket integrity.
• If compression is normal, proceed to the next step.