P0420 on GMC ACADIA — Catalyst System Efficiency Below Threshold Bank 1

Q: "What does P0420 mean on a GMC ACADIA?"

"P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 2 GMC ACADIA owners have reported this to NHTSA."

Q: "What are the most common causes of P0420 on GMC ACADIA?"

"Based on 2 NHTSA reports, the most commonly cited components are: Power Train,Electrical System,Fuel/Propulsion System, Engine. These percentages are based on the component field in owner complaints."

Q: "Is P0420 serious on my GMC ACADIA?"

"Of 2 NHTSA reports for this code on GMC ACADIA, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic."

Q: "What should I do if my GMC ACADIA 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 GMC ACADIA

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.

2 GMC ACADIA owners have reported this issue to NHTSA across model years 2017-2019. Most reports come from the 2017, 2019 model years. The most commonly reported component is Power Train,Electrical System,Fuel/Propulsion System (50.0% of reports).

Real GMC ACADIA Owner Reports

Source: NHTSA Complaints Database

"I was traveling at the posted speed limit of 80 mph on [XXX] in South Dakota at [XXX] and the GMC Acadia was working without any issue when all of a sudden various warnings flashed on the dashboard with one of them being power saver mode engaged."

— 2017 GMC ACADIA owner · POWER TRAIN,ELECTRICAL SYSTEM,FUEL/PROPULSION SYSTEM · Filed 08/07/2024

"Owner of a 2019 GMC Acadia Denali (VIN: [XXX] , current odometer ~87,164 miles), purchased new. In early February 2026, the check engine light came on."

— 2019 GMC ACADIA owner · ENGINE · Filed 02/20/2026

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

📊 Complaint Trend by Model Year

1

'17

1

'19

Common Causes on GMC ACADIA

Based on NHTSA complaint component analysis for this vehicle.

POWER TRAIN,ELECTRICAL SYSTEM,FUEL/PROPULSION SYSTEM 50%

ENGINE 50%

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 GMC ACADIA? ▾

P0420 indicates: Catalyst System Efficiency Below Threshold Bank 1. This is a emission controls code. 2 GMC ACADIA owners have reported this to NHTSA.

What are the most common causes of P0420 on GMC ACADIA? ▾

Based on 2 NHTSA reports, the most commonly cited components are: Power Train,Electrical System,Fuel/Propulsion System, Engine. These percentages are based on the component field in owner complaints.

Is P0420 serious on my GMC ACADIA? ▾

Of 2 NHTSA reports for this code on GMC ACADIA, none involved a crash or fire. However, any diagnostic code should be evaluated by a qualified mechanic.

What should I do if my GMC ACADIA 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.