What does code P0420 mean on a Toyota and is it safe to drive?
P0420: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means on your Toyota, what usually causes it, what repairs typically cost, and how safe it is 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 for your Toyota
- 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 Toyota, repairs for P0420 often fall between $400 and $2400, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Toyota
Toyota P0420 is extremely common on V6 models using the 2GR-FE. The downstream O2 sensor heat shield on Camry and RAV4 frequently contacts the frame, chafing the wiring harness—this causes a false P0420 before the cat itself fails. Inspect the B1S2 sensor connector for corrosion or chafed insulation before condemning the converter. On Prius, P0420 usually means the smaller downstream cat has genuinely failed. On Tacoma 4.0 V6, inspect for exhaust manifold cracks which create a pre-sensor leak and skew cat efficiency readings.
Most commonly affected models