2010 Acura P0420: What It Means & Is It Safe to Drive?
P0420 on the 2010 Acura: 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 2010 Acura
- 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 2010 Acura, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Acura
Acura P0420 on 3.5L J35 V6 engines (MDX, TL, Pilot) is similar to Honda—the rear downstream O2 sensor connector corrodes at the undercarriage mounting point. Clean and dielectric-grease all O2 sensor connections before replacing the catalyst. On RDX 2.3T with the K23A1 turbo engine, turbo inlet air leaks cause lean conditions that can trigger P0420 after the ECU long-fuel-trim logic interprets sensor data. TL SH-AWD 3.7L has two cats and requires checking P0430 (bank 2) simultaneously. OEM Acura cats are expensive; OEM Honda equivalents often fit at lower cost.
Most commonly affected models