p0420
Call a Pro
Toyota · SUVs
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Toyota SUVs means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
4Runner TRD Pro 2024Grand Highlander Limited 2024Highlander XLE 2024Highlander Hybrid Bronze Edition 2023Land Cruiser 1958 Edition 2024RAV4 XLE Premium 2024RAV4 Hybrid SE 2024Sequoia Capstone 20244Runner Limited 20244Runner SR5 20244Runner TRD Off-Road 2024Grand Highlander Platinum 2024Grand Highlander XLE 2024Highlander LE 2024Highlander Limited 2024Highlander Platinum 2024RAV4 Adventure 2024RAV4 LE 2024RAV4 TRD Off-Road 2024RAV4 XLE 2024Sequoia Limited 2024Sequoia Platinum 2024Sequoia SR5 2024Sequoia TRD Pro 2024Venza Limited 2024
Likely Causes
How to Fix It
1
Check for other stored DTCs that may be causing secondary catalyst damage
2
Compare upstream and downstream O2 sensor waveforms to assess catalyst efficiency
3
Measure catalyst inlet and outlet temperatures with an infrared thermometer
4
Inspect the exhaust system for leaks between the manifold and converter
5
Replace the catalytic converter if confirmed failed and repair any root cause issues
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter (Bank 1)
Downstream oxygen sensor
Exhaust gaskets
Exhaust hardware kit
Related Error Codes