Post Catalyst Fuel Trim System Too Lean (Bank 1)

Check these first

• Exhaust leak between the exhaust manifold and catalyst
• Failed or weak downstream oxygen sensor
• Faulty catalyst condition
• Fuel system pressure faults
• Engine misfire under load

What to do next

1. Check for exhaust leaks ahead of the catalyst
2. Compare downstream sensor activity to fuel trims
3. Verify catalyst efficiency with a scan tool
4. Review fuel trims at idle and load for a real lean condition
5. Repair the leak, sensor, or fuel issue and clear the code

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