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ItalianoP0420 Catalyst System Efficiency Below Threshold (Bank 1)
The ECU compares the signals of the upstream and downstream oxygen sensors to estimate the oxygen storage capacity of the catalytic converter. P0420 is set when the downstream signal follows the upstream signal too closely, indicating that catalyst efficiency is below the threshold.
Common causes
- Worn, contaminated or damaged catalytic converter
- Catalytic converter removed or replaced with a non-compliant unit
- Faulty downstream or upstream oxygen sensor
- Exhaust leaks near the sensors
- Misfires or oil consumption that have damaged the catalyst
Typical symptoms
- Check engine light (MIL) on
- Emissions test failure
- Usually no noticeable change in drivability
- Sulphur smell or reduced performance if the catalyst is restricted
P0420 and NuoVolta
If the catalytic converter has been removed or replaced for off-road or motorsport use, where permitted by law, the NuoVolta Catalyst Removal solution (with Lambda / O2 Removal for the downstream sensor where needed) adjusts the ECU calibration and the DTC removal feature can disable this code. On a road vehicle, check the sensors, exhaust leaks and misfires first.
Diagnose and repair real faults first. Removing or disabling emission systems is only permitted where allowed by law, for example for off-road or motorsport use.