P0420 on Peugeot
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Peugeot vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 1 Peugeot model — most commonly on 206. 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 Peugeot range from $100 to $900, 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 Peugeot by Model
Peugeot 206(1 issue)
- 'Anti-Pollution Fault' Warning — Emissions System Faults2000-2012
A very common 206 complaint on multiplexed cars is the 'Anti-pollution fault' message on the multifunction display, often accompanied by the engine management light, misfire, lost power or limp mode. It is a generic emissions-system alert triggered by a range of root causes documented across owner forums: failing ignition coils, lambda (oxygen) sensor faults, sticking EGR valves, sticky hydraulic tappets and, on neglected cars, catalytic converters damaged by sustained misfiring. Because the message is generic, owners frequently replace the wrong parts before reading the stored fault codes.
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View P0420 across all makes →Frequently Asked Questions
What does P0420 mean on Peugeot?▼
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 Peugeot specifically, this code is documented across 1 model.
What causes P0420 on Peugeot vehicles?▼
Common causes on Peugeot: 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 Peugeot?▼
Repair costs on Peugeot range from $100 to $900, depending on the specific model and root cause.
Which Peugeot models have P0420 documented?▼
Au7o has documented P0420 on 1 Peugeot model: 206.