Last reported case: 5 months ago
Based on 11 owner reports, 11 from forums)
What is P0420?
P0420 indicates your catalytic converter is not cleaning exhaust gases effectively, typically triggered by a failing converter or upstream engine issues. This powertrain code is moderately serious and can affect emissions and performance, with Honda vehicles like the Accord and CR-V appearing most frequently in reports. Based on 975 repair cases, the average repair cost is $3847, ranging from $0 to $4700.
Common Causes:
- Failing catalytic converter (most common cause based on code definition)
- Upstream oxygen sensor malfunction
- Exhaust leaks before the catalytic converter
- Engine misfires or rich/lean fuel mixture affecting converter efficiency
Symptoms:
- Check Engine Light illuminated (primary symptom)
- Reduced fuel economy reported by some owners
- Possible lack of power during acceleration
- No noticeable symptoms in some cases beyond the warning light
🚗P0420 on 2020 TOYOTA Tundra
This page focuses specifically on P0420 issues reported by 2020 TOYOTA Tundra owners. The experiences and fixes below are from real owners of this exact vehicle.
Symptoms Reported by 2020 TOYOTA Tundra Owners:
Parts Often Involved:
What Owners Say
Real experiences from 2020 TOYOTA Tundra owners
“To be thorough, I replaced all 4 sensors with Denso’s and yet I’m still getting the codes. I don’t have a fancy reader but what I have noticed is that the two upstreams read the nearly identical outputs under load and idle.”View original
“Been doing a lot of reading and it seems the consensus was that these two showing up together is usually a red herring for bad upstream sensors. To be thorough, I replaced all 4 sensors with Denso’s and yet I’m still getting the codes.”View original
“He used Toyota parts on everything so I'm betting he didn't cheap out on the plugs. The P0420 code is just "catalyist system efficiency below threshold (bank 1)".”View original
“My problems start in the 20mph range and don’t get better til after 40mph. If I try to accelerate quickly it will downshift into a lower gear but not really go any faster.”View original
“I don't know what spark plugs were used the but the guy I bought the truck from did things right. He used Toyota parts on everything so I'm betting he didn't cheap out on the plugs.”View original
“I've had a recurring P0420 code. catalyst system efficiency of your car is below threshold (Bank 1) Now the light stays on. I just decided to try to swap bank 1 to bank 2 to see if the code follows, but the downstream on bank 2 has a short pigtale.”View original
“I just decided to try to swap bank 1 to bank 2 to see if the code follows, but the downstream on bank 2 has a short pigtale. Bank 1 has a long pigtale, so swapping won't be an option.”View original
“If I try to accelerate quickly it will downshift into a lower gear but not really go any faster. It does begin to rattle at that point and I’ve seen a CEL come and go.”View original
“P0420 with dropping exhaust temperatures and lean fuel trim I hate to be that guy who asks about cat codes for the millionth time, but because so many smooth brains like me ask dumb questions I haven't been able to find a thread with similar problems as mine.”View original
“I have read shifty's links on P0420. Here's some background info: - Upstream o2 on both banks appear to have the normal fluctuations between lower and higher voltage - Downstream o2's mimic the upstream.”View original
These are real experiences shared by 2020 TOYOTA Tundra owners on automotive forums and communities. Results may vary based on vehicle condition and repair quality.
About This Data
This page aggregates 11 discussions about P0420 from 2020 TOYOTA Tundra owners across automotive communities.
Success rate (0%) is calculated from posts where owners confirmed whether their fix resolved the issue.
Last updated: 9/25/2025