Fuel and injectionGeneric OBD-II codeUrgency: Monitor
Code P2177: lean mixture off idle (bank 1)
P2177 means: system too lean off idle (bank 1): the mixture has too much air relative to fuel with the throttle partly open.[1] The ECU has detected a lean air-fuel mixture, with too much air, on bank 1 when the engine is not idling (at part load). On some diagnostic tools it appears as "P/T" for "part throttle".[1]
What code P2177 means
The ECU has detected a lean air-fuel mixture, with too much air, on bank 1 when the engine is not idling (at part load). On some diagnostic tools it appears as "P/T" for "part throttle".[1]
It is a generic code, but the manufacturer may define it slightly differently, so consult the car's manual.[1]
Original definition (SAE J2012): System Too Lean Off Idle (Bank 1)[1]
Causes of P2177
From most to least likely, according to the sources.
- 1Unmetered air entry: vacuum leaks or faulty intake hoses and gaskets.[1][2]
- 2Dirty or failed mass airflow sensor.[1][2]
- 3Faulty or blocked injectors, or a failed fuel pressure regulator.[1][2]
- 4Fuel pump not giving enough pressure, or a blocked fuel filter.[1][2]
- 5Exhaust leak or faulty oxygen sensor, which can distort the reading.[1]
- 6Damaged wiring or connectors for engine sensors and actuators; in rare cases, the ECU.[1][2]
Symptoms
- Engine warning light on.[1][2]Engine warning light: faults that cause it
- Loss of engine performance.[1][2]Less power: faults that cause it
- Increased fuel consumption.[1][2]Uses more fuel: faults that cause it
- Misfires, jerking and uneven running.[1][2]Jerking: faults that cause it
How to diagnose P2177
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the codes and the bank 1 fuel trim values; look for other lean mixture codes.[1]
- 2Look for air leaks: cracked intake hoses, manifold gaskets and vacuum pipes.[2]
- 3Check the mass airflow sensor (cleanliness and reading) before replacing it.[2]
- 4Check the fuel pressure, the filter and the operation of the injectors.[2]
- 5Check the exhaust for leaks and the condition of the oxygen sensor and the sensor wiring.[1][2]
Can I keep driving with P2177?
Monitor
The sources consulted do not specify the severity. A sustained lean mixture can cause misfires and loss of performance, so get it diagnosed without leaving it too long.[1][2]
Documented faults related to P2177
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.
Injectors: the most serious faults by engine and car
- High severityFrequency: Very frequentOM651Delphi piezo injector failure (220/250 CDI)Yes: 220 and 250 CDI models built between 2008 and 2011 had Delphi piezo injectors that were prone to failing and seizing in the cylinder head. Mercedes-Benz replaced them under warranty in 2009 and switched the 220 CDI to solenoid injectors from 2010-2011, but the 250 CDI kept them.Repair (garage): €3,600–€5,900
- High severityFrequency: CommonBMW N52 / N53N53 piezoelectric injector failureThe N53's piezoelectric direct injectors fail frequently and cause misfires, rough idle and limp mode; replacing them is expensive and they must be coded.
- High severityFrequency: CommonMZR-CDOil dilution from leaking injector seals and DPF regenerationsOn the 2.0 and 2.2 MZR-CD, injector seals that age badly and incomplete particulate filter regenerations on short journeys can let unburnt diesel into the sump, diluting the oil and leaving the engine with less lubrication.
- High severityFrequency: CommonOM642Wear and failure of the Bosch piezo injectorsThe OM642's Bosch piezo injectors can fail from around 150,000-200,000 km, especially with poor-quality diesel; they cannot be repaired, only replaced. Because it is a V engine, those on the rear bank are harder to reach, which pushes up labour costs.Repair: €4,500–€6,500
Fuel pump and high-pressure pump: the most serious faults by engine and car
- Critical severityFrequency: Common2.0 and 2.5 HybridLow-pressure fuel pump failure: loss of power and fire riskYes: a low-pressure fuel pump with a defective impeller (Denso) affects millions of Toyotas and Lexuses, including Corolla, C-HR, RAV4 and Camry models with these engines. It can cause loss of power or stalling, and in the EU there is also a risk of leaks and fire on 2018-2022 Corolla, C-HR and Auris models.
- High severityFrequency: CommonBMW N54/N55High-pressure fuel pump (HPFP) failureThe N54's high-pressure pump is one of its best-documented failures: most units will have had it replaced at some point. It warns of itself with long cranking and loss of power; the 2010 campaign was US-only.
- High severityFrequency: Common2.2/2.5 dCiInjection pump or injector failureThe 2.2 dCi's common rail injectors fail fairly often on the X-Trail and Almera, with cases of seizing and leaks; on the Almera with the older YD22DDT, the documented fault is in the injection pump electronics, not the injectors.
- High severityFrequency: CommonVW 2.0 TFSI EA113Wear of the high-pressure pump cam followerYes: the 2.0 TFSI EA113's high-pressure fuel pump is driven by the camshaft through a follower (tappet) that wears; if it wears through it can damage the pump or the camshaft, so it should be checked and replaced as a preventive measure.Repair (garage): €250–€900Appears at around 90,000 km
Frequently asked questions
What is the difference between P2177 and P2187?
According to the standard's definition, P2177 is set off idle (at part load) and P2187 when the engine is idling. Both are for bank 1.[1]
Can I drive with P2177?
The sources set no limit. If the car runs normally it can get to a garage, but a sustained lean mixture can cause misfires and poor performance, so do not put off the check.[1][2]
Is it always a vacuum leak?
No. It is one of the causes, but it can also be the mass airflow sensor, the injectors, the fuel pressure or an exhaust leak.[1][2]
What is bank 1?
It is the side of the engine where cylinder number 1 is. On four-cylinder inline engines only that bank exists.[1]
Will I pass the MOT with code P2177?
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.[3]
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.
- P2177: System Too Lean Off Idle (Bank 1)CarParts.com · Technical documentation · consulted 29 October 2026
- OBD DTC Fehlercode P2177CarWiki · 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