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Home/Cars/BMW/3 Series/E90/E91 (2005-2012)/how to fix P0420 code in BMW 3 Series E90/E91 (2005-2012) for good?

how to fix P0420 code in BMW 3 Series E90/E91 (2005-2012) for good?

BMW 3 Series E90/E91 (2005-2012)

Severity: mediumDifficulty: mediumError Code: P04202-4 hours
3 min read
587 words

Problem Statement

## Problem Statement The P0420 code in a BMW 3 Series E90/E91 (2005-2012) indicates a catalyst system efficiency below the threshold for Bank 1, suggesting potential issues with the catalytic converte

Error Code
P0420
Repair Time
2-4 hours

Safety Warnings

  • ⚠Safety Warnings:**
  • ⚠Disconnect battery before working on electrical systems.
  • ⚠Allow engine to cool before opening exhaust components.

Symptoms

  • •Check engine light illuminated
  • •Poor fuel economy
  • •Decreased engine performance
  • •Failed emissions test
  • •Unusual exhaust odors (e.g., sulfur smell)
  • •Increased engine noise (potentially from the exhaust)

Diagnostic Steps

  1. 1Scan the vehicle's onboard diagnostics (OBD-II) for error codes and freeze frame data.
  2. 2Inspect the exhaust system for visible leaks or damage.
  3. 3Check the condition and readings of the upstream (pre-catalytic) oxygen sensor.
  4. 4Measure the temperature before and after the catalytic converter using a temperature probe.
  5. 5Inspect the catalytic converter for physical damage or blockage.
  6. 6Test for proper fuel trims using a live data stream.

Solution

Solution

1. Preparation

  • Gather tools and parts.
  • Disconnect the vehicle battery to ensure safety.
  • Allow the engine to cool down before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

  1. Remove the upstream oxygen sensor:
    • Use an oxygen sensor socket to carefully unscrew the sensor from the exhaust manifold.
    • Tools Required: Oxygen sensor socket, ratchet, and extension.
  2. Install the new oxygen sensor:
    • Apply anti-seize compound to the threads of the new sensor (if not pre-applied).
    • Screw it in by hand, then tighten to manufacturer specifications (usually around 30 lb-ft).
  3. Reinstall the sensor connector:
    • Ensure the connector is clean and secure.

3. Inspect and Replace Catalytic Converter (if necessary)

  1. Remove the exhaust components:
    • Unbolt the exhaust pipe sections leading to the catalytic converter.
    • Tools Required: Socket set, penetrating oil (if bolts are rusted).
  2. Remove the catalytic converter:
    • Unbolt the catalytic converter from its mountings.
    • Check for any obstruction or damage.
  3. Install the new catalytic converter:
    • Position the new converter and secure it with the bolts, tightening to manufacturer specifications.
    • Check for proper alignment to prevent exhaust leaks.

4. Reset the Engine Control Unit (ECU)

  1. Reconnect the battery:
    • Ensure all connections are secure before reconnecting.
  2. Clear the OBD-II trouble codes:
    • Use an OBD-II scanner to erase the P0420 code and any other related codes.

5. Test Drive

  • Drive the vehicle under various conditions to ensure the check engine light does not reappear and the performance improves.

Verification

After completing the repair, verify that the issue has been resolved:

  • Test the affected component to ensure it functions correctly
  • Check for any error codes or warning lights
  • Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

  • •Follow the manufacturer's recommended maintenance schedule
  • •Address warning signs early before they develop into major issues
  • •Use quality parts and fluids recommended for your vehicle
  • •Keep detailed records of all repairs and maintenance

Tools & Equipment Required

  • Install the new oxygen sensor:**
  • Apply anti-seize compound to the threads of the new sensor (if not pre-applied).
  • Screw it in by hand, then tighten to manufacturer specifications (usually around 30 lb-ft).
  • Reinstall the sensor connector:**
  • Ensure the connector is clean and secure.

Parts Required

  • Upstream oxygen sensor
  • Catalytic converter (if faulty)

Additional Information

Error CodeP0420
Repair Time

2-4 hours

Difficulty

medium

Severity

medium

Tools

5 items

Parts

2 items

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