P0420 and P0430: catalytic converter efficiency
The oxygen sensor after the catalytic converter sees almost the same signal as the one before it, so the engine computer concludes the converter is no longer storing and cleaning enough. P0420 is bank 1, P0430 bank 2.
SeverityModerateUsually not urgent today, but it can get worse if left.
Can you keep driving?Drive gently, check it soonWhat does P0420 mean?
A working converter stores oxygen and evens out the exhaust, so the downstream sensor reads a fairly flat signal while the upstream one switches quickly. When the two start to look alike, the converter's efficiency is judged below the legal threshold. The code describes how the converter measures; it does not prove the converter is the part to replace.
What causes P0420?
- A converter that has aged, or been damaged by misfires or by the engine burning oil
- An exhaust leak ahead of or near the downstream oxygen sensor
- A slow or failing downstream oxygen sensor
- An engine problem that upsets the mixture, such as a misfire or a rich condition
- A replacement converter that does not meet the original specification
What to check first for P0420
- Fix any misfire, mixture or sensor code first: they can cause P0420 and will ruin a new converter
- Look and listen for exhaust leaks, especially at the joints near the sensors
- Have both sensor signals compared on a scan tool with the engine fully warm
- Only then judge the converter itself
Can you drive with P0420?
In the short term it is usually safe to keep driving, because the car runs normally. Get it checked soon: emissions are higher, the car can fail an inspection, and if the cause is a misfire the converter can be destroyed.
Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.
Codes on this page
10
- P0420Catalyst System Efficiency Below ThresholdBank 1
- P0421Warm Up Catalyst Efficiency Below ThresholdBank 1
- P0422Main Catalyst Efficiency Below ThresholdBank 1
- P0423Heated Catalyst Efficiency Below Threshold
- P0424Heated Catalyst Temperature Below Threshold
- P0430Catalyst System Efficiency Below Threshold
- P0431Warm Up Catalyst Efficiency Below Threshold
- P0432Main Catalyst Efficiency Below Threshold
- P0433Heated Catalyst Efficiency Below Threshold
- P0434Heated Catalyst Temperature Below Threshold
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
