Why P0420 Keeps Tripping Every Time This Code Isn’t What You Think

Thu, 16 Apr 2026 21:45:16 +0000

Why P0420 Keeps Tripping: Understanding the Real Causes (Not What You Think) The P0420 diagnostic trouble code (DTC) is one of the most frustrating codes for car owners and mechanics alike. It signals a "Catalyst System Efficiency Below Threshold" — a warning that your vehicle’s catalytic converter isn’t filtering exhaust emissions effectively. But here’s what many don’t realize: P0420 often triggers unnecessarily — and not because your catalytic converter is truly failing. In this article, we’ll explore why the P0420 keeps tripping even when your catalyst isn’t the issue, and what EPA guidelines, wiring faults, and system mismatches really mean for your car. --- ### What P0420 Really Means (and What It Doesn’t)