P0420 on Infiniti
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Infiniti vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 1 Infiniti model — most commonly on FX35. P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault. Typical repair costs on Infiniti range from $600 to $3,500, depending on the specific model and root cause.
Common Causes of P0420
- •Worn-out or failing catalytic converter (Bank 1)
- •Faulty or aged downstream (or upstream) oxygen sensor
- •Exhaust leak before or near the oxygen sensors
- •Engine running rich or lean (fuel trim issues)
- •Misfires or oil/coolant contaminating the converter
- •Damaged or aftermarket low-quality catalytic converter
- •Faulty oxygen sensor wiring or connectors
- •Software/calibration needing update (on some vehicles)
P0420 on Infiniti by Model
Infiniti FX35(1 issue)
- Catalytic Converter Efficiency Failure (P0420 / P0430)2003-2008
First-generation FX35s commonly set P0420 and/or P0430 (catalyst efficiency below threshold, bank 1/bank 2) as the two close-coupled converters degrade, often between 80,000 and 130,000 miles. Contributing causes on this engine are oil consumption coating the catalyst and rich running from failed coils/plugs or sensor faults. Dealers quote about $1,500 per converter plus labor, with the OEM manifold-integrated cats being the expensive part. Aftermarket high-flow cats compatible with the G35/350Z are a common lower-cost route, and replacing downstream O2 sensors alone often does not clear the code.
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What does P0420 mean on Infiniti?▼
P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)." P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault. On Infiniti specifically, this code is documented across 1 model.
What causes P0420 on Infiniti vehicles?▼
Common causes on Infiniti: Worn-out or failing catalytic converter (Bank 1), Faulty or aged downstream (or upstream) oxygen sensor, Exhaust leak before or near the oxygen sensors, Engine running rich or lean (fuel trim issues), Misfires or oil/coolant contaminating the converter. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0420 on a Infiniti?▼
Repair costs on Infiniti range from $600 to $3,500, depending on the specific model and root cause.
Which Infiniti models have P0420 documented?▼
Au7o has documented P0420 on 1 Infiniti model: FX35.