P0420 on Nissan Altima
Catalyst System Efficiency Below Threshold Bank 1
Methodology: Reviewed against the SAE J2012 generic DTC definition and NHTSA owner-complaint patterns, then scoped to Nissan Altima context without treating complaints as confirmed diagnoses.
Sources: SAE/OBD-II definitions, manufacturer service information, and public reliability reports (including NHTSA where applicable).
- SAE J2012 Diagnostic Trouble Code Definitions — Generic diagnostic trouble code definition reference for P0420.
- NHTSA recalls, complaints, and manufacturer communications — Used to check public owner complaint context, recall status, and safety-related manufacturer communications by VIN or vehicle.
Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.
What P0420 Means on Your Nissan Altima
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.
Real Nissan Altima Owner Reports
Source: NHTSA Complaints Database
"I already went though p0420 issue few years back and i got it again. nissan dealer charged me whole lotta money to fix the issue and the warning sign came back again. went to local auto zone and it show p0420 again. please help."
"This year i am required to obtain a smog test for my 2005 nissan altima tha i purchased used from power volvo in california. my car is throwing off a p0420 code which requires a replacement to the pre-catalytic converter."
"Car arbitrarily stalled and cut off at low speeds and began to also jerk intermittently as if attempting to shut down while traveling at highway speeds...easily this could lend to a collision!!! service engine soon indicator illuminated on dash and has remained lit."
All reports filed by vehicle owners directly with the U.S. Department of Transportation.
📊 Complaint Trend by Model Year
Common Causes on Nissan Altima
Based on NHTSA complaint component analysis for this vehicle.
What To Do Next
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1
Check for recalls on YOUR VIN
Go to nhtsa.gov/recalls and enter your VIN. If your vehicle is covered, repairs are free.
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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.
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3
Compare repair quotes
Get 2–3 quotes. Dealer vs. independent shop prices often differ 30–50% for the same repair.