2006 Nissan P0420: What It Means & Is It Safe to Drive?
P0420 on the 2006 Nissan: 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.
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 Nissan
- 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 Nissan, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Nissan
Nissan Altima 2.5L QR25DE is notorious for early catalyst failure—many cats fail before 100k miles. This is widely acknowledged; OEM replacement is the reliable fix. On Maxima and Pathfinder with VQ35DE, P0420 and P0430 often appear together (both bank cats failing simultaneously). Sentra CVT seal leaks can allow transmission fluid into the exhaust indirectly via engine contamination, accelerating cat degradation. On newer Rogues, confirm the rear O2 sensor connector hasn't corroded at the undercarriage clip point.
Most commonly affected models