Fuel and injectionGeneric OBD-II codeUrgency: Garage soon
Code P0170: fuel trim malfunction (bank 1)
P0170 means: fuel trim malfunction (bank 1): the correction the control unit applies to the air-fuel mixture goes outside the expected limits.[1][2][3] The control unit constantly corrects the amount of fuel it injects based on what the lambda sensor measures in the exhaust; that correction is the fuel trim. The P0170 is stored when, on bank 1, the correction reaches the limit of what the control unit can apply and the air-fuel mixture still does not end up within the expected range.[1][2][3][4][5]
What code P0170 means
The control unit constantly corrects the amount of fuel it injects based on what the lambda sensor measures in the exhaust; that correction is the fuel trim. The P0170 is stored when, on bank 1, the correction reaches the limit of what the control unit can apply and the air-fuel mixture still does not end up within the expected range.[1][2][3][4][5]
Unlike the P0171 (lean mixture: too much air or too little fuel) and the P0172 (rich mixture), the P0170 does not specify in which direction the correction has run out: it can be either. To find out, you have to look at the fuel trims with a scan tool: a positive value indicates that the control unit is adding fuel because the mixture is lean, and a negative one that it is taking fuel away because it is rich.[2][5][6][7][8]
'Bank 1' is the group of cylinders that includes cylinder number 1. Inline four-cylinder engines usually have a single bank, while V6s, V8s and some four-cylinder engines have two. The P0173 is the equivalent code for bank 2.[4][7][8]
It is a generic OBD-II code (it starts with P0), so it means the same on any make; what changes from one engine to another is the most likely cause.[3][9]
Original definition (SAE J2012): Fuel Trim Malfunction (Bank 1)[1][2][3]
Causes of P0170
From most to least likely, according to the sources.
- 1Air entering that the MAF sensor does not measure: cracked or loose vacuum hoses or intake hoses, intake manifold gasket, crankcase ventilation (PCV) or brake servo leaks.[1][2][4][5]
- 2Dirty, contaminated or faulty mass air flow (MAF) sensor, which measures the incoming air wrongly.[1][2][4][5]
- 3Incorrect fuel pressure, either low (weak pump, blocked filter) or high (faulty pressure regulator).[1][2][4][5]
- 4Bank 1 injectors that are blocked, dirty, dripping or stuck open.[1][2][4][5]
- 5Faulty, slow or contaminated front lambda sensor on bank 1, which gives the control unit wrong information. The sources do not agree on how much weight to give it: Autodoc Club puts it first on its list, while Carista and AutoDTCs place it after the air and fuel causes.[1][2][4][5]
- 6Exhaust leaks before the front lambda sensor, which can distort its reading.[1][4][5]
- 7Misfires, from faulty spark plugs or coils.[1][4]
- 8Causes cited by only one source: dirty air filter (Autodoc Club) and a fuel vapour (EVAP) purge valve stuck open (Carista).[1][2]
Symptoms
- Engine warning light on, often together with the P0171 or the P0172.[2][4][5]Engine warning light: faults that cause it
- Loss of power and weak response when accelerating.[1][2][4]Less power: faults that cause it
- Rough idle, with the revs oscillating.[1][2][5]Vibrations: faults that cause it
- Hesitation or jerking when accelerating, and the odd occasional misfire.[2][5]Jerking: faults that cause it
- The engine may stall at idle or when coming to a stop.[4][5]Engine stalls: faults that cause it
- Increased fuel consumption.[1][2][4][5]Uses more fuel: faults that cause it
- Hard starting, especially when cold.[1]Hard to start: faults that cause it
- Black smoke from the exhaust, which AutoDTCs associates with a rich mixture.[1][5]Black smoke: faults that cause it
- Smell of fuel when the mixture is rich.[5]Fuel smell: faults that cause it
How to diagnose P0170
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the code and the freeze frame data with a scan tool and see whether other codes are stored, especially the P0171 or P0172 (which say in which direction the mixture has drifted) and, on two-bank engines, the P0173, P0174 or P0175. Carista recommends treating those accompanying codes as the main route of the diagnosis.[2][4][5]
- 2Carry out a visual inspection of the engine bay: intake hoses and vacuum hoses free of cracks and not disconnected, manifold gaskets and connections in good condition, and the air filter housing properly closed.[1][4]
- 3Watch the bank 1 short-term and long-term fuel trims live, with the engine warm, at idle and at about 2,500 rpm: positive is a lean mixture and negative, rich. The sources give different ranges: Ross-Tech considers values around ±10% normal, and AutoDTCs speaks of ±5% at idle and ±8% under load as normal and puts the code threshold beyond ±25%. The exact limit depends on the manufacturer.[2][5][6][10]
- 4Interpret the pattern. A high deviation at idle that falls as the revs rise points to an air leak (vacuum is highest at idle); one that persists or gets worse under load points to the fuel supply. If the deviation appears mainly at higher revs, Ross-Tech and Samarins think of the MAF sensor (Samarins adds the blocked catalytic converter and low fuel pressure), whereas AutoDTCs describes the MAF sensor as a similar positive deviation at idle and under load: the patterns are indicative.[6][7][10]
- 5If the mixture is lean, look for leaks with a smoke test on the intake and the vacuum circuit, and clean or check the MAF sensor, confirming that its readings make sense.[1][2][5][10]
- 6Check the fuel pressure with a gauge, together with the fuel filter, the pump and the pressure regulator.[1][2][5]
- 7If the mixture is rich, check whether any injector is dripping or stuck open, the EVAP purge valve and whether the fuel pressure is excessive.[2][5]
- 8Also check for exhaust leaks before the lambda sensor, the crankcase ventilation and the ignition system (spark plugs and coils).[1][4][5]
- 9Evaluate the front lambda sensor last, once air and fuel have been ruled out.[2][5]
- 10After the repair, clear the adaptation values and use the scan tool to check that the fuel trims return to normal values.[5][10]
Can I keep driving with P0170?
Garage soon
The two sources that assess urgency agree that you can drive for a while, although not with the same emphasis. Autodoc Club allows short trips, asks you to go to a workshop as soon as possible and warns that the fault can damage the engine and increase emissions. AutoDTCs rates it moderate: you can normally drive, but a mixture that stays rich or lean increases consumption and can harm the catalytic converter, so it should be repaired soon. Carista and PartsAvatar make no assessment.[1][2][4][5]
Parts related to code P0170
The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.
Injector
Fuel pump
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Documented faults related to P0170
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 the P0170, P0171 and P0172?
All three concern the bank 1 fuel correction. The P0171 expressly indicates a lean mixture (too much air or too little fuel) and the P0172, a rich mixture. The P0170 is the general version: it says the correction has reached its limit without specifying in which direction, and it often appears together with one of the other two. To find out which way the mixture has drifted, you have to look at the sign of the fuel trims with a scan tool (positive, lean; negative, rich). The P0173 is the equivalent for bank 2.[2][4][5][6][7][8]
Can I drive with the P0170 code?
Yes, for a while and without demanding too much of the engine, but it is best to repair it soon. Autodoc Club allows short trips and warns that the fault can damage the engine and increase emissions; AutoDTCs rates it moderate and points out that a drifting mixture makes the car use more fuel and can harm the catalytic converter.[1][5]
Do I need to replace the lambda sensor when the P0170 appears?
Not necessarily. The sensor is one of the possible causes, but it is best to rule out air leaks, the MAF sensor, the fuel pressure and the injectors first, as these are the causes that most sources cite. Live fuel trims help decide where to start.[2][4][5][6][10]
What is bank 1 and why does the P0173 sometimes appear as well?
Bank 1 is the group of cylinders that includes cylinder number 1. On a two-bank engine (V6, V8 and some four-cylinder engines), the control unit calculates the correction for each bank separately, and the P0173 is the same warning for bank 2. Comparing the trims of both banks helps to see whether the fault is in just one or affects both.[4][5][7][8][10]
Will I pass the MOT with the P0170 active?
If the code keeps the engine warning light on, no: according to Diariomotor, that light is a serious defect in the ITV (the Spanish roadworthiness inspection) and, on Euro 5 and Euro 6 cars, the inspection also reads the OBD system.[11]
Does the P0170 mean the same on all makes?
Yes. Codes starting with P0 are generic OBD-II codes (defined by the SAE) and have the same definition for all manufacturers; what varies from one engine to another is the part that tends to fail.[3][9]
Will I pass the MOT with code P0170?
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.[12]
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.
- Código OBD2 P0170: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
- P0170: OBD-II code P0170 flags a general fuel trim malfunction on bank 1Carista · Technical documentation · consulted 2 October 2026
- P0170: Fuel Trim Malfunction (Bank 1)The Automotive Technician (TaT) · Technical documentation · consulted 2 October 2026
- Guide To P0170 OBD Error Code SolutionsPartsAvatar · Technical documentation · published 13 March 2023 · consulted 2 October 2026
- P0170 – Fuel Trim Bank 1 — Symptoms, Causes & FixAutoDTCs · Technical documentation · published August 2026 · consulted 2 October 2026
- Fuel Trim InfoRoss-Tech Wiki · Technical documentation · consulted 2 October 2026
- Code P0171 - System Too Lean: Symptoms, causes, common problems, diagnosticSamarins.com · Technical documentation · published 10 July 2021 · consulted 2 October 2026
- Code P0172 - System Too Rich: Symptoms, causes, common problems, diagnosticSamarins.com · Technical documentation · published 25 June 2023 · consulted 2 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 2 October 2026
- Fuel Trim Diagnostics: Short Term vs. Long Term Fuel Trim ExplainedAutoDTCs · Technical documentation · consulted 2 October 2026
- 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
- 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