P0420 on Peugeot: How to Diagnose & Fix
Catalyst System Efficiency Below Threshold (Bank 1)
1 Peugeot model · 1 documented issue · $100-$900 repair
P0420 on Peugeot by model: symptoms, diagnosis and fix
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.
Common Symptoms
- 'Anti-pollution fault' message on the multifunction display
- Engine management light on
- Misfire or juddering, especially under load
- Loss of power or limp mode
- Engine cutting out shortly after the warning appears
How to Fix
Read the stored DTCs with PSA-capable diagnostics rather than guessing; the accepted fixes are replacing the specific failed component — most commonly an ignition coil pack or lambda sensor, cleaning or replacing the EGR valve, or replacing a misfire-damaged catalytic converter in advanced cases.
Sources for this issue (3)
P0420 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0420 mean on a 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 it is documented across 1 model: 206.
What are the most common causes of P0420?
The most common causes of P0420 are: 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). The specific cause varies by vehicle.
How much does it cost to fix P0420 on a Peugeot?
Published repair estimates on Peugeot range from $100 to $900 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0420 on a different make?
View P0420 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.