Toyota 1.0 VVT-i (1KR-FE)Engine sensorsCatalytic converterLambda sensor
Faulty lambda sensor (P0420 code) on the 1.0 VVT-i on the 1.0 VVT-i
Why this rating?
Low severity: A nuisance or wear. It does not immobilise the car or damage other parts.
Frequency occasional: Gebrauchtwagenberater.de describes it as a fault that appears 'frequently' on the Aygo and its 107/C1 twin, and Fiches-auto.fr includes lambda sensors among the points to watch on the Aygo II and the 108. They are independent sources, but none gives figures for affected units, so we rate it occasional rather than common.[1][2][3][4]
Symptoms
- Engine warning light on with code P0420 (catalytic converter efficiency below threshold) in the fault memory.[1][2]Engine warning light: other faults that cause it · Garage soon
- Abnormal consumption or irregular engine running if the sensor sends an inconsistent signal to the control unit.[4]Uses more fuel: other faults that cause it · Monitor
Why it happens
The sensor upstream of the catalytic converter degrades with mileage and stops giving a reliable signal; its contacts or connector can also fail, which is why they are recommended to be checked before replacing the part.[1]
Fiches-auto.fr adds that an inconsistent sensor falsifies the mixture correction and causes the warning light, abnormal consumption or irregular running.[4]
If it is not repaired: Fiches-auto.fr links it to the warning light, abnormal consumption and irregular running; the sources do not document mechanical damage to the engine.[4]
Affected cars and years
Gebrauchtwagenberater.de cites it for the first generation (2005-2014) of the Aygo/107/C1, and Fiches-auto.fr also includes it on the Aygo II and 108 (2014-2021), which use the same engine.[1][2][3][4]
| Version | Years | Codes |
|---|---|---|
| 1.0 VVT-i 67-69 hp (1KR-FE, 2005-2018) | 2005–2018 | 1KR-FE |
| 1.0 VVT-i 71-72 hp (1KR-FE, 2018-2022) | 2018–2022 | 1KR-FE |
Models fitted with the affected versions
Citroën
- Citroën C1 I2005–2014
- Citroën C1 II2014–2022
Peugeot
- Peugeot 1072005–2014
- Peugeot 1082014–2021
Toyota
- Toyota Aygo I2005–2014
- Toyota Aygo II2014–2022
- Toyota iQ2008–2015
- Toyota Aygo X2022–2025
How much it costs to repair
Includes: Lambda sensor (oxygen sensor) and replacement labour.[1]
None of the sources consulted publishes a euro quote for this repair.
Prices in Spain, including VAT. A workshop hour costs on average €38–66 at independent garages and €77–134 at dealerships in Spain, depending on the region and the brand. How we calculate costs
How to check for it before buying a used car
- Read the fault memory: an isolated P0420 is not enough to condemn the catalytic converter; first check the upstream sensor and its wiring.[1]
- Ask whether the sensor has already been replaced and at what mileage, especially on cars with more than 150,000 km.
Parts needed
The part or kit that fixes this fault, according to the sources.
Upstream lambda sensor (before catalytic converter)
Measures oxygen in the exhaust gases so the control unit can correct the fuel mixture.
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How to prevent it
- Check and clean the sensor connector contacts before replacing the part, as Gebrauchtwagenberater.de recommends.[1]
Recalls, campaigns and claims
As of 30 October 2026, we have no record of recalls, campaigns or extended manufacturer warranties for this fault. Check with an official dealer using the chassis (VIN) number: they will tell you whether the car has any outstanding campaign.
What owners say
Frequently asked questions
Does a P0420 on an Aygo, C1 or 107 mean the catalytic converter is faulty?
Not necessarily. Gebrauchtwagenberater.de says that on this engine the cause is usually the upstream lambda sensor, which weakens with high mileage; that is why it is checked before replacing the catalytic converter.[1][2]
Can you keep driving with the lambda sensor warning light on?
Fiches-auto.fr says an inconsistent sensor falsifies the mixture correction and can cause abnormal consumption or an engine that runs roughly; so it is worth diagnosing and repairing it rather than living with the warning light.[4]
What can you do now?
We will put you in touch with a partner only if you authorise it in the form.
Other 1.0 VVT-i faults
- Medium severityFrequency: CommonClutchPremature clutch wearThe clutch is by far the most cited fault among owners of the Aygo, C1 and 107/108 with this engine: between 13% and 41% of the reviews collected by fiches-auto.fr for each of the four cars mention it.
- Medium severityFrequency: CommonCoolingCoolant leak from the water pumpThe water pump is the second most cited fault on the first-generation Aygo, C1 and 107 (2005-2014): between 16% and 24% of the fiches-auto.fr reviews mention it, although it does not appear in the more limited data for the Peugeot 108.
- High severityFrequency: RareOther2010 recall for the accelerator pedalIn January 2010 Toyota recalled, as part of a worldwide campaign, the Aygo, Peugeot 107 and Citroën C1 built between February 2005 and August 2009 because of an accelerator pedal that could stay partly depressed or return slowly to idle.
- Low severityFrequency: RareLubricationOil consumption: no documented patternUnlike other small engines of its era, oil consumption does not appear as a widespread problem on the 1.0 VVT-i: it accounts for between 1% and 4% of the reviews recorded by fiches-auto.fr for the Aygo, C1 and 107/108.
- Low severityFrequency: RareCylinder head and blockHead gasket and exhaust gasket: no documented patternThe head gasket does not appear as a relevant problem on the 1.0 VVT-i either: between 0 and 2 cases out of more than 200 reviews on the C1 and 107/108, and it does not even appear as a category of its own in the Aygo data consulted.
More faults with the engine sensors on other engines and cars
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: OccasionalBMW B57AdBlue/SCR system fault (NOx sensors, heater and pump)A specialist garage considers the B57's AdBlue/SCR system the fault that most often leaves cars immobilised: a NOx sensor, the quality sensor, the heater or the pump usually fails, and topping up the tank rarely stops the countdown of remaining starts.
- Medium severityFrequency: Occasional1.2 8v FireSensor failures: lambda sensor and crankshaft position sensor (TDC)The 1.2 8v Fire can suffer sensor faults: the lambda sensor (warning light, rough running) and, in the Fiat Punto, the crankshaft position sensor (TDC sensor), linked to misfires. These are minority issues, but they recur across several models with this engine.
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Sources
Every fact on this page links to its source. If you find an error, let us know.
- Toyota Aygo (I & II): Schwachstellen, Probleme & KaufberatungGebrauchtwagenberater.de · Motoring press · published 12 April 2023 · consulted 30 October 2026 · in German
- Peugeot 107: Probleme und SchwachstellenGebrauchtwagenberater.de · Motoring press · consulted 30 October 2026 · in German
- Tous les problèmes sur Toyota AYGO 2 2014-2021Fiches-auto.fr · Owners' forum · consulted 30 October 2026 · in French
- Tous les problèmes sur Peugeot 108 2014-2021Fiches-auto.fr · Owners' forum · consulted 30 October 2026 · in French