P0420 on Acura
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Acura vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 1 Acura model — most commonly on TSX. 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 Acura range from $300 to $1,800, 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 Acura by Model
Acura TSX(1 issue)
- Catalytic Converter Efficiency Loss Setting P04202004-2014
TSX owners across both generations report recurring P0420 (Catalyst System Efficiency Below Threshold, Bank 1) as the front catalytic converter loses efficiency. On the first-generation K24A2 cars this is frequently a downstream consequence of the oil-consumption problem - oil ash coats and poisons the catalyst substrate long before its normal service life. On the V6 cars the J-series family is separately documented for the catalyst substrate breaking apart, producing a loose rattle inside the converter shell. Beyond the check engine light, the practical consequence is a failed emissions inspection. Catalytic converters carry the federal 8-year/80,000-mile emissions warranty, which most of these cars are now well past.
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What does P0420 mean on Acura?▼
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 Acura specifically, this code is documented across 1 model.
What causes P0420 on Acura vehicles?▼
Common causes on Acura: 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 Acura?▼
Repair costs on Acura range from $300 to $1,800, depending on the specific model and root cause.
Which Acura models have P0420 documented?▼
Au7o has documented P0420 on 1 Acura model: TSX.