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

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

"P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 6 HONDA ODYSSEY owners have reported this to NHTSA."

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

"Based on 6 NHTSA reports, the most commonly cited components are: Engine And Engine Cooling,Structure, Power Train, Engine. These percentages are based on the component field in owner complaints."

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

"Of 6 NHTSA reports for this code on HONDA ODYSSEY, 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 ODYSSEY 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 ODYSSEY

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.

6 HONDA ODYSSEY owners have reported this issue to NHTSA across model years 2005-2019. Most reports come from the 2019, 2005 model years.

Real HONDA ODYSSEY Owner Reports

Source: NHTSA Complaints Database

"Strong vibration felt in passenger compartment and steering wheel when driving at 40 to 45 mph. there was a droning noise as well. this has been an issue since 2010, but identified by dealer service advisor only in feb 2014. quoted 800 dollars to replace both front engine mounts."

— 2005 HONDA ODYSSEY owner · ENGINE AND ENGINE COOLING,STRUCTURE · Filed 04/05/2010

"Honda issued a recall on the fuel pump December 2023. They did not have any parts available to replace mine. I had brought in my Odyssey Elite to Space Coast Honda multiple times before the recall stating my engine wouldn't crank. I was unable to get the fuel pump replaced until December 5, 2024."

— 2018 HONDA ODYSSEY owner · POWER TRAIN · Filed 06/06/2025

"While driving, the check engine light appeared and the vehicle began running rough and hesitating during acceleration."

— 2019 HONDA ODYSSEY owner · ENGINE · Filed 02/26/2026

"Life-Threatening Acceleration Lag: The vehicle is experiencing severe power loss during critical driving moments, for example, while entering intersections or attempting to re-accelerate into moving traffic."

— 2019 HONDA ODYSSEY owner · ENGINE,FUEL/PROPULSION SYSTEM · Filed 01/19/2026

"The contact owns a 2019 Honda Odyssey. The contact stated that the emission warning light was illuminated. The vehicle was taken to an independent mechanic, where a diagnostic scanner was used to retrieve diagnostic trouble codes P0420 and P0430."

— 2019 HONDA ODYSSEY owner · FUEL SYSTEM, GASOLINE · Filed 04/28/2023

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

📊 Complaint Trend by Model Year

1

'05

1

'18

4

'19

Common Causes on HONDA ODYSSEY

Based on NHTSA complaint component analysis for this vehicle.

ENGINE and ENGINE COOLING,STRUCTURE 16.7%

POWER TRAIN 16.7%

ENGINE 16.7%

ENGINE,FUEL/PROPULSION SYSTEM 16.7%

FUEL SYSTEM, GASOLINE 16.7%

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 ODYSSEY? ▾

P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 6 HONDA ODYSSEY owners have reported this to NHTSA.

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

Based on 6 NHTSA reports, the most commonly cited components are: Engine And Engine Cooling,Structure, Power Train, Engine. These percentages are based on the component field in owner complaints.

Is P0420 serious on my HONDA ODYSSEY? ▾

Of 6 NHTSA reports for this code on HONDA ODYSSEY, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic.

What should I do if my HONDA ODYSSEY 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.