how to fix P0303 misfire code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before performing any work.

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, torque wrench, gap gauge
• Remove the engine cover if necessary.
• Locate the spark plug for cylinder 3, typically found under the ignition coil.
• Remove the ignition coil by unscrewing the retaining bolts and carefully pulling it out.
• Unscrew the spark plug using a socket wrench.
• Inspect the spark plug for wear (burnt electrodes, excessive carbon buildup).
• If necessary, replace with a new spark plug, ensuring the gap is correct according to manufacturer specifications (usually between 0.028-0.031 inches).
• Reinstall the ignition coil and secure it with bolts.

3. Check and Replace Ignition Coil (if needed)

• If swapping the ignition coil showed that cylinder 3 is still misfiring, replace the ignition coil.
• Tools Required: Socket set, torque wrench
• Remove the faulty ignition coil as described in the previous step.
• Install the new ignition coil, ensuring it is seated properly.
• Reconnect wiring harness to the ignition coil.

4. Inspect and Clean/Replace Fuel Injector

• Tools Required: Fuel injector removal tool, cleaning solvent (if cleaning), socket set
• Locate the fuel injector for cylinder 3.
• Disconnect the fuel line carefully (use a rag to catch any fuel drips) and remove the injector retaining clips.
• Remove the fuel injector.
• Inspect for clogs; if dirty, either clean it or replace with a new injector.
• Reinstall the fuel injector, securing it with clips and reconnecting the fuel line.

5. Compression Test (if misfire persists)

• Tools Required: Compression tester
• Remove the spark plug for cylinder 3.
• Insert the compression tester into the spark plug hole.
• Crank the engine and note the reading; it should be within the manufacturer’s specified range (usually around 150-200 psi).
• If compression is low, further engine diagnostics may be necessary.