P0420 on HONDA ACCORD — Catalyst System Efficiency Below Threshold Bank 1

Q: "What does P0420 mean on a HONDA ACCORD?"

"P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 4 HONDA ACCORD owners have reported this to NHTSA."

Q: "What are the most common causes of P0420 on HONDA ACCORD?"

"Based on 4 NHTSA reports, the most commonly cited components are: Engine, Power Train,Engine, Power Train,Engine,Fuel/Propulsion System. These percentages are based on the component field in owner complaints."

Q: "Is P0420 serious on my HONDA ACCORD?"

"Of 4 NHTSA reports for this code on HONDA ACCORD, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic."

Q: "What should I do if my HONDA ACCORD shows P0420?"

"1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare."

What P0420 Means on Your HONDA ACCORD

P0420 is a diagnostic trouble code indicating: Catalyst System Efficiency Below Threshold Bank 1. This code relates to the emission controls system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

4 HONDA ACCORD owners have reported this issue to NHTSA across model years 2007-2013. Most reports come from the 2007, 2008 model years. The most commonly reported component is Engine (50.0% of reports).

Real HONDA ACCORD Owner Reports

Source: NHTSA Complaints Database

"I just bought the car and had it 1 week and i was driving to work when the check engine light came on suddenly and car started misfiring. this happened right when i was stopped at a light and turned on my a/c. 3 codes came on which were p0420, p0139, and p2647."

— 2007 HONDA ACCORD owner · POWER TRAIN,ENGINE · Filed 07/17/2020

"In 2008, i purchase a new honda accord v6 paid with financing $25,000. i purchase a brand new vehicle to not have to be bothered with someone else problems. when my car reached 100 thousand miles in the winter, i heard a loud knocking sound under the hood and i was loosing a lot of oil."

— 2008 HONDA ACCORD owner · POWER TRAIN,ENGINE,FUEL/PROPULSION SYSTEM · Filed 04/03/2019

"My 2010 honda accord has had a check engine light for a p0420 code at 110k miles. for someone that knows something about cars, a catalytic converter should not be going out this soon."

— 2010 HONDA ACCORD owner · ENGINE · Filed 05/13/2016

"After service at honda service station at rosenberg, tx... i had issues with the temperature sensor in the front of the grill, also a code showed up 2 days later, along with check engine light... when scanned it was "p0420"..."

— 2013 HONDA ACCORD owner · ENGINE · Filed 11/19/2019

All reports filed by vehicle owners directly with the U.S. Department of Transportation.

📊 Complaint Trend by Model Year

1

'07

1

'08

1

'10

1

'13

Common Causes on HONDA ACCORD

Based on NHTSA complaint component analysis for this vehicle.

ENGINE 50%

POWER TRAIN,ENGINE 25%

POWER TRAIN,ENGINE,FUEL/PROPULSION SYSTEM 25%

What To Do Next

1
Check for recalls on YOUR VIN
Go to nhtsa.gov/recalls and enter your VIN. If your vehicle is covered, repairs are free.
2
Get a proper diagnosis
A code alone doesn't tell you the exact failed part. A diagnostic at a shop ($50–$150) pinpoints the root cause before you spend money on parts.
3
Compare repair quotes
Get 2–3 quotes. Dealer vs. independent shop prices often differ 30–50% for the same repair.

Frequently Asked Questions

What does P0420 mean on a HONDA ACCORD? ▾

P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 4 HONDA ACCORD owners have reported this to NHTSA.

What are the most common causes of P0420 on HONDA ACCORD? ▾

Based on 4 NHTSA reports, the most commonly cited components are: Engine, Power Train,Engine, Power Train,Engine,Fuel/Propulsion System. These percentages are based on the component field in owner complaints.

Is P0420 serious on my HONDA ACCORD? ▾

Of 4 NHTSA reports for this code on HONDA ACCORD, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic.

What should I do if my HONDA ACCORD shows P0420? ▾

1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare.