Blog
P0420 Doesn't Always Mean a New Catalytic Converter
We regularly meet drivers who've been quoted a catalytic converter for a P0420 code when the actual cause is a cracked flex pipe or a tired sensor. Here's why this happens so often.
What P0420 actually measures
The computer compares the upstream and downstream oxygen sensors. If the downstream sensor looks too much like the upstream one, it decides the converter isn't doing anything. But a lazy downstream sensor, an exhaust leak letting in air, or a misfire dumping fuel all produce the same picture.
What we check first
- Sensor response on live data
- Exhaust leaks with a smoke test
- Misfire history and fuel trims
- Oil or coolant consumption that would poison a converter
When it really is the converter
Old age, a long-ignored misfire, or a broken substrate rattling around. Then we replace it with a direct-fit unit — after fixing whatever killed the first one.
Related services
We do this in your driveway
- Fuel & Exhaust
Catalytic Converter Replacement
Failed or stolen converter replaced with a direct-fit unit — after we confirm it actually failed.
- Fuel & Exhaust
Oxygen Sensor Replacement
O2 and air-fuel sensor replacement for codes like P0135, P0141, and P0171 — done in your driveway.
- Fuel & Exhaust
Exhaust Leak & Manifold Repair
Ticking on cold start, loud exhaust, or fumes in the cabin — leaks found and fixed on site.
- Diagnostics & Inspections
Check Engine Light Diagnostics
A real diagnosis with a professional scan tool, not just a code read from the parts store.
Ready when you are.
Text or call with your vehicle and what's going on. We'll confirm a window and bring the parts.