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P0420
P0420: Catalyst efficiency below threshold
Severity: Medium — not urgent, but don't ignore it
P0420 means the computer sees the Bank 1 catalytic converter isn't cleaning exhaust efficiently, judged by comparing the upstream and downstream oxygen sensors.
Possible causes
- Worn or clogged catalytic converter.
- Faulty rear or front oxygen sensor.
- Exhaust leak before the sensor.
- Engine misfires or running rich for a long time.
Before replacing the converter
Converters are expensive, so first check the O2 sensors, exhaust leaks and any misfire codes. Watch live sensor data — if the rear sensor switches just like the front one, the converter is likely weak.
How RA-150 helps
Plug the Raqib RA-150 into the OBD port, open the app and tap Scan: you get the exact code, a plain explanation, and the AI assistant tells you what to do. After the repair you can clear the code and check it doesn't return.
Read the code yourself with Raqib RA-150
Bluetooth scanner + Arabic app and AI assistant. Made and packaged in Egypt.