2006 Alfa Romeo P0420: What It Means & Is It Safe to Drive?
P0420 on the 2006 Alfa Romeo: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
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What this code means
The downstream oxygen sensor detects that the catalytic converter is not storing or converting exhaust properly. This is one of the most common check engine codes.
Common causes on the 2006 Alfa Romeo
- Failed or aging catalytic converter
- Faulty downstream oxygen sensor
- Exhaust leak before or after the catalyst
- Engine misfire or rich/lean condition damaging the catalyst
Symptoms
- Check Engine Light on
- Often no drivability issues
- Possible failed emissions test
- Rotten egg smell in some cases
Typical fixes
- Replace catalytic converter
- Replace oxygen sensor(s)
- Repair exhaust leaks
- Fix underlying fuel/ignition issues first
Repair cost range
For a 2006 Alfa Romeo, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Alfa Romeo
P0420 is relatively uncommon on newer Alfa Romeo models but has been reported on the 2.0T engine. Verify exhaust integrity and upstream O2 sensor function before replacing the catalyst.
Most commonly affected models
Giulia 2017+Stelvio 2018+