P0420 Catalyst system efficiency below threshold, bank 1
- System
- Powertrain - engine and transmission
What P0420 means
"Catalyst system efficiency below threshold, bank 1" is a comparison between two sensors, not a measurement of the converter itself. The computer watches the oxygen sensor ahead of the catalytic converter and the one behind it, and judges the converter by how different the two readings are; this code is filed when that difference fell below the threshold it expects. P0430 is the same comparison on bank 2.
This is a standard code. It means the same thing on every make of vehicle.
What the program shows for P0420
O2 sensor (rear) and Catalyst temp are on the Dashboard, and the Full scan's on-board self-tests report the catalyst result for each bank as PASS, FAIL or NO RESULT against the car's own limits. The Inspection screen says whether the catalytic converter monitor has finished, and Clear codes warns that clearing resets it.
The Dashboard shows Commanded EGR, EGR error, Evap purge, Catalyst temp, O2 sensor (rear), Fuel level and Coolant temp. The Full scan's On-board self-tests list the Catalyst bank, EGR / VVT bank, EVAP leak, EVAP purge flow, EVAP purge valve and Secondary air results as PASS, FAIL or NO RESULT against the car's own limits, and the Inspection screen shows whether the Catalytic converter, Fuel vapour system, Exhaust gas recirculation and Secondary air injection monitors are done or still running. Clear codes warns that clearing resets those monitors.
See how the program shows a code →