2007 Buick P0420: What It Means & Is It Safe to Drive?
P0420 on the 2007 Buick: 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 2007 Buick
- 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 2007 Buick, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Buick
Buick's 3.6L V6 (LFX/LY7) is prone to P0420 after high mileage. Oil consumption from worn piston rings or valve seals accelerates catalyst failure; check for blue smoke at cold startup.
Most commonly affected models
Enclave 2008–2012Regal 2011–2017LaCrosse 2010–2016