Powertrain
generic / SAE
P0420
Catalyst System Efficiency Below Threshold (Bank 1)
The oxygen storage capacity of the main catalytic converter on bank 1 has degraded below the OBD threshold. The downstream oxygen sensor signal increasingly mirrors the upstream sensor, indicating reduced conversion efficiency.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number4 / 20
Possible causes
- Catalyst aged or contaminated high
- Downstream oxygen sensor drift medium
- Exhaust leak before catalyst low
- Long-term misfire damage low
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Inspection / repair
- Difficulty: hard
- DIY: shop recommended
- Estimated cost: 600–2500 €
- Estimated time: 1.5–5 h
- Component: catalytic converter
- Component: oxygen sensor upstream
- Component: oxygen sensor downstream
- MIL / check engine light
- emissions-relevant
- drive cycle required
Sources
References
sae:J2012
iso:15031-6