Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Garage soon

P0420 on Renault: causes and affected engines

P0420 means: catalyst system efficiency below threshold (bank 1).^[1][2] Renault has 9 documented faults that can trigger it, across 8 engines, including 1.2 TCe, 1.4 and 1.6 16v, 1.2 16v and 1.0 SCe (B4D). Only a diagnosis can confirm the cause on your car.

Documented faults

that can trigger it

Engines

used by Renault, with at least one of them

Renault models

with at least one of these faults

Urgency

Garage soon

Reviewed on 5 October 20265 sources How we work

Documented faults in Renault engines that can trigger P0420

Grouped by engine or model, from most to least important. These are faults with the injectors, with the ignition coils and with oil consumption: not all of them will necessarily set the code, and only a diagnosis confirms the cause on your car.

1.2 TCe

In Captur I, Clio IV, Kadjar, Kangoo II, Mégane III, Mégane IV and Scénic III

- Critical severityFrequency: CommonLubricationExcessive oil consumption and engine failure1.2 TCe and 1.2 DIG-T engines built from 2012 to mid-2016 can burn more than 1 litre of oil per 1,000 km because the piston rings do not seal properly; carbon damages the valves and the engine can fail. There was no recall: the dealer network reprograms and replaces rings or the engine.Repair: €5,000–€10,000

1.4 and 1.6 16v

In Clio II, Clio III, Fluence, Kangoo I, Laguna II, Mégane I and 5 more models

- Medium severityFrequency: Very frequentIgnitionIgnition coil failureThe individual ignition coils are the most-cited fault of the K4J/K4M in the European Renault versions: they fail frequently and cause jerking, loss of power and the engine warning light coming on. It is a cheap electrical part to replace, not internal engine damage.Appears at around 30,000 km

1.2 16v

In Clio II, Clio III, Clio IV, Kangoo I, Modus, Twingo I and Twingo II

- Medium severityFrequency: CommonIgnitionIgnition coil failure (misfires, engine warning light)The ignition coil is the engine fault that recurs most on the 1.2 16v: it appears independently on the Renault Clio II and Clio III, with misfires, jerking or the engine warning light coming on.

1.0 SCe (B4D)

In Twingo III

1.3 TCe

In Captur II, Clio V, Kadjar, Mégane IV and Scénic IV

- Medium severityFrequency: OccasionalInjectionUnstable idle, juddering and stalling caused by the injectorsOn 1.3 TCe/DIG-T engines built before April 2019, the injector seal may be missing or its housing incorrectly sized, which causes an unstable idle, juddering and stalling. Renault-Nissan corrected it at the factory in 2019; the repair involves replacing injectors or, in serious cases, the cylinder head.

1.4 and 1.6 8v

In Clio II, Kangoo I and Mégane I

- Medium severityFrequency: OccasionalIgnitionIgnition coil failureThe ignition coils fail in a minority of reports for the Clio II and the Dacia Sandero I with this engine, in a considerably smaller proportion than on the 16-valve evolution of the same block. They cause jerking and the engine warning light, but do not damage the engine.

2.0 16v F4R and F4RT

In Laguna II, Mégane II and Mégane III

- Medium severityFrequency: OccasionalIgnitionF4RT ignition coil failureIgnition coils are a recurring weak point of the Mégane RS 2.0 turbo F4RT: when they fail there is hesitation, rough running and misfires. It is an electrical part fault, not internal engine damage.

0.9 TCe

In Captur I, Clio IV and Twingo III

- Low severityFrequency: RareLubricationOil consumption (uncommon on this engine)Unlike other engines in the same family, the 0.9 TCe does not show a widespread pattern of excessive oil consumption: the sources document only a minority of cases.

Common causes of P0420 on any make

From most to least likely, according to the sources.

1Worn or damaged catalytic converter that no longer stores and releases oxygen properly. It is the most common cause, especially on high-mileage cars.^[2][3][4]
2Faulty or aged lambda sensor, or one with a poor electrical connection. The rear one can give a wrong signal that mimics a bad catalytic converter; if the front one fails, the mixture goes out of control and can end up damaging the catalytic converter.^[1][2][3][4]
3Exhaust leaks before the catalytic converter or between the sensors (manifold, pipes or the catalytic converter itself), which distort the oxygen measurement.^[1][2][4]
4An underlying problem that punishes the catalytic converter: misfires, a leaking injector, a mixture that is too rich or too lean, an engine burning oil, or coolant entering the cylinders through the head gasket. The catalytic converter is then the victim and, if the cause is not fixed, the new one will be ruined just the same.^[1][2][3][4]

What to check first

The first diagnostic steps, from the most likely and cheapest to check to the most expensive.

1Read all the stored codes and the freeze-frame data with a diagnostic tool. If there are misfire, mixture or sensor codes, resolve them first and check again: they may be the real cause of the P0420.^[2][3]
2Look for technical service bulletins or manufacturer campaigns for your model: in some cases they recommend a simpler fix than replacing the catalytic converter, such as updating the ECU software.^[4]
3Check the exhaust from the manifold to the sensors for leaks and repair them before going on with the tests, because they distort the readings.^[1][4]

Full guide to P0420: symptoms, diagnosis and whether you can drive

Frequently asked questions

Which Renault engines have faults that can trigger P0420?

1.2 TCe (1 fault), 1.4 and 1.6 16v (1 fault), 1.2 16v (1 fault), 1.0 SCe (B4D) (2 faults), 1.3 TCe (1 fault) and 1.4 and 1.6 8v (1 fault). Each fault has its own page with the affected years and versions, the symptoms and the repair cost.

What does code P0420 mean on a Renault?

Catalyst system efficiency below threshold (bank 1). The ECU monitors the catalytic converter by comparing the two lambda sensors in the exhaust, the one before it and the one after it. With a healthy catalytic converter, the rear sensor's signal stays steady even though the front one oscillates; when the two look too alike, the ECU concludes that the catalytic converter no longer cleans the exhaust gases well enough and stores the code. It is a generic OBD-II code: it means the same on a Renault as on any other make.^[1][2][4]

Can I keep driving with P0420?

Garage soon. The sources do not fully agree. Autodoc Club considers it minor, Mechanic Base says it is not an urgent repair and Carista notes that the engine usually runs normally. Even so, Mechanic Base advises against driving like this, and Samarins warns that only a workshop can assess the risk after an initial diagnosis: in some cars, pieces of ceramic from the broken catalytic converter can get back into the cylinders and score their walls. There is no need to stop the car, but it should be diagnosed soon; also, a fault in the emissions system can cause a failure at the ITV (Spain's roadworthiness inspection, similar to the MOT) (RACE).^{[1][2][3][4][5]}

Sources

Every fact on this page links to its source. If you find an error, let us know.

Código de avería P0420: guía paso a paso para su diagnóstico y resoluciónAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
P0420 Code - Meaning, Causes & How to fix itMechanic Base · Technical documentation · published 7 November 2025 · consulted 2 October 2026
P0420: OBD-II code P0420 means the bank 1 catalytic converter isn't reducing emissions enoughCarista · Technical documentation · consulted 2 October 2026
Code P0420 Catalyst Efficiency Below Threshold (Bank 1)Samarins.com · Technical documentation · published 8 October 2022 · consulted 2 October 2026
¿Qué es el sistema antipolución del coche y qué averías puede sufrir?RACE · Motoring press · published 25 September 2026 · consulted 2 October 2026 · in Spanish