KlaroP0420
MODERATECatalyst System Efficiency Below Threshold (Bank 1)
What this code means
The catalytic converter no longer cleans the exhaust as well as expected. Often linked to an ageing converter or to untreated misfires.
Catalytic converter, exhaust gas recirculation, particulate filter, fuel vapour. These faults rarely leave you stranded, but they fail the roadworthiness test and become expensive if left alone.
How to read this code
- PPowertrain
- 0standardised code
- 4Emission controls
- 20P0420
The letter P names the system: Powertrain. The digit 0 that follows marks a standardised code, shared by all manufacturers code. The next digit, 4, locates the fault: emission controls.
What to do
Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.
Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back.