Lambda sensorsGeneric OBD-II codeUrgency: Monitor
Code P2270: rear lambda sensor stuck lean (B1S2)
P2270 means: oxygen sensor: signal biased or stuck lean (bank 1, sensor 2).[1][2] The bank 1 rear oxygen sensor (the one downstream of the catalytic converter) continuously indicates a lean mixture. The ECU tests it by forcing mixture changes and seeing whether the sensor follows them; the signal stays fixed at a low value.[1][2]
What code P2270 means
The bank 1 rear oxygen sensor (the one downstream of the catalytic converter) continuously indicates a lean mixture. The ECU tests it by forcing mixture changes and seeing whether the sensor follows them; the signal stays fixed at a low value.[1][2]
Some manufacturers call these downstream sensors "catalyst monitor sensors". Bank 1 is the one that contains cylinder 1.[1][2]
Original definition (SAE J2012): O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 2)[1][2]
Causes of P2270
From most to least likely, according to the sources.
- 1Failed, degraded rear sensor, or one contaminated by silicone, coolant or oil.[1][2][3]
- 2Exhaust leak upstream of the sensor or in the catalytic converter body, letting in air and making the reading lean.[1][2][3]
- 3Damaged or corroded wiring or connector; a signal wire shorted to ground lowers the voltage.[1][2]
- 4Bank 1 and bank 2 rear sensor connectors swapped over, on engines with two banks.[2]
- 5A genuinely lean mixture, which usually also gives other codes.[1][3]
- 6ECU fault, rare.[1][3]
Symptoms
- Engine warning light on; according to CarParts.com, it is the only noticeable symptom.[1][2]Engine warning light: faults that cause it
- Possible slight increase in consumption if there is also another mixture fault.[3]Uses more fuel: faults that cause it
How to diagnose P2270
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the codes and the freeze-frame data. If there are codes for the front sensor or the mixture (P0171, P0172), deal with them first.[2]
- 2Confirm which is bank 1 (the one with cylinder 1) and check that the rear sensor connectors have not been swapped.[1][2]
- 3With the diagnostic tool, watch the rear sensor voltage with the engine warm; a healthy sensor should rise when the mixture is briefly enriched.[2]
- 4Check there are no exhaust leaks between the catalytic converter and the sensor, and check the sensor's wiring and connector.[1][2][3]
- 5Measure the sensor heater's resistance and, if everything is fine, replace the rear sensor.[2]
Can I keep driving with P2270?
Monitor
The sources agree that it normally does not affect driving: the front sensor keeps controlling the mixture. The risk is that the catalytic converter goes unmonitored and the car fails the emissions inspection, so get it repaired within a few weeks.[1][2]
Documented faults related to P2270
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Engine sensors: the most serious faults by engine and car
- 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.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- High severityFrequency: OccasionalM264/M254Poorly tightened 48 V earth wiring in the mild-hybrid system (fire risk)Mercedes-Benz has issued several recalls (2022-2025) because the 12 V and 48 V earth connections of some cars with a 48 V system may be poorly tightened: resistance rises, the connection heats up and a fire cannot be ruled out. The official workshop checks them and repairs them if necessary in an hour or more.
- High severityFrequency: Occasional1.9 TDIUnit injector tappet wear and injector wiring damageOn the unit injector system, the tappets that operate the injectors can wear if the oil is not changed on time, and the injector wiring can be damaged by contact with oil, causing misfires or loss of power.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Frequently asked questions
Does P2270 affect consumption or power?
In most cases no: the front sensor keeps regulating the mixture and the only noticeable symptom is the warning light.[1][2]
Can I drive with P2270?
Yes, in the short term. Get it repaired within a few weeks because the rear sensor checks the catalytic converter and the fault can stop the car passing the MOT emissions test.[2]
Does the sensor always have to be replaced?
No. First rule out exhaust leaks, damaged wiring and connectors swapped between banks.[1][2]
What is the difference from P2195?
P2195 refers to the front sensor (sensor 1), which controls the mixture; P2270 is the rear one (sensor 2), which monitors the catalytic converter. That is why the consequences differ.[1][2]
Will I pass the MOT with code P2270?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[4]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P2270: O2 Sensor Signal Biased/Stuck Lean (Bank 1, Sensor 2)CarParts.com · Technical documentation · consulted 29 October 2026
- P2270 - O2 Sensor Signal Stuck Lean Bank 1 Sensor 2AutoDTCs · Technical documentation · consulted 29 October 2026
- OBD DTC Fehlercode P2270CarWiki · Technical documentation · consulted 29 October 2026 · in German
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish