how to diagnose the P0302 code in BMW 3 Series E90/E91 (2005-2012)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to ensure safety.
• Allow the engine to cool before beginning work.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket
• Remove the engine cover if necessary.
• Use a spark plug socket to remove the spark plug from cylinder 2.
• Inspect the spark plug for signs of fouling or damage.
• Install a new spark plug, ensuring it is gapped correctly (typically around 0.032-0.036 inches for BMWs).
• Torque the spark plug to the manufacturer's specifications (usually around 18 lb-ft).

3. Inspect and Replace Ignition Coil

• Tools Required: Socket set
• Remove the ignition coil for cylinder 2 by unscrewing any retaining bolts and disconnecting the electrical connector.
• Inspect the coil for cracks or damage.
• If necessary, replace the ignition coil with a new one, ensuring it's seated properly.

4. Test and Replace Fuel Injector

• Tools Required: Noid light or multimeter
• Disconnect the fuel injector connector from cylinder 2.
• Use a noid light or multimeter to test for signal at the connector.
• If there is no signal, trace the wiring or replace the injector if it fails the test.

5. Perform Compression Test

• Tools Required: Compression tester
• Remove the spark plug from cylinder 2.
• Insert the compression tester into the spark plug hole.
• Crank the engine and record the compression reading.
• Compare with specifications (typically around 140-200 psi) to determine cylinder health.

6. Check for Vacuum Leaks

• Tools Required: Smoke machine or carb cleaner
• Inspect vacuum lines connected to the intake manifold for cracks or looseness.
• Use a smoke machine to detect leaks or spray carb cleaner around the intake to check for changes in idle.