P0420moderate Severity
Catalyst System Efficiency Below Threshold (Bank 1)
The downstream oxygen sensor is detecting that the catalytic converter on Bank 1 is not operating at maximum efficiency to reduce emissions.
Common Symptoms
- Check Engine Light illuminated
- Failed emissions test
- Smell of sulfur or 'rotten eggs' from the exhaust (if completely failed)
Generic Causes
- Failing or degraded catalytic converter
- Exhaust leak before the O2 sensor
- Faulty upstream or downstream O2 sensor
- Prolonged engine misfires damaging the catalyst
Known Cars Affected by P0420
We have cross-referenced P0420 against our database of known faults. Below are specific cars where this code frequently appears, along with the detailed diagnostic and repair instructions for that specific vehicle.
We don't currently have any specific car faults recorded in our database that trigger the P0420 code. However, the generic causes listed above should guide your diagnostic process.