Toyota Verso OBDII P0171 Fault Code Diagnosis | train resource (2023)

One of the most common trouble codes with the Toyota Verso is P0171. This suggests that your Toyota Verso is leaning to one side of the seat. It is the most common code related to the air/fuel mixture.

Not the most complicated OBDII trouble code to diagnose. It is also one of the most common codes.

The most common causes of P0171 are a bad oxygen sensor, a vacuum leak, or a dirty MAF sensor.

DefinitionP0171: Clean Fuel Compensation System (Bank 1).
SymptomsCheck engine light, poor fuel economy, misfire, hard to find idle.
common causesDirty MAF sensor, vacuum leak, O2 sensor.
Risk of breakage?Rarely, but driving with a P0171 can sometimes damage other components.
Repair cost (parts)It varies, but the most common repairs are usually under $200.
difficulty of repairCommon P0171 repairs are usually simple.


  • Definition
  • Symptoms
  • Reasons
  • Usual corrections
  • Questions

P0171 Definition: Lean Bank 1 Fuel Trim System

P0171 is a generic code, meaning it has the same definition for the Toyota Verso as any other vehicle.

(Video) How to Fix TOYOTA P0171 Engine Code in 3 Minutes [2 DIY Methods / Only $8.37]

fuel compensation system

The ideal air/fuel ratio is 14.7:1 (14.7 parts air to one part fuel). Your car's fuel trim system manages the air/fuel ratio and adjusts it when the powertrain control unit deems it necessary (it can vary from 12.0:1 for power to 16.0:1 for economy).

  • O2 sensors– Oxygen sensors measure the exhaust and report the oxygen content to the powertrain control unit.
  • MAF or MAP sensor– Depending on the model year of your Verso, it may have a mass air flow sensor or manifold absolute pressure sensor (or both). Their job is to measure the air entering the engine.
  • Train control unit– It receives information from these sensors and uses it to adjust the air/fuel ratio.

Sistema Lean

The code is triggered when the oxygen sensors detect that the air-fuel mixture is "lean" (too much air or too little fuel).

The vehicle's PCM will add more fuel to the mixture to bring the air-fuel mixture to where it needs to be for optimal combustion. It also throws the P0171 code to let you know that this has been done.

Banco 1

Bank 1 is the side of your Toyota Verso's engine with the first cylinder. You only need to worry about this if you have two heads. If your car has four or six cylinders in a row, there will only be one bank of cylinders.

Symptoms of Code Verse P0171

There are usually no drivability problems associated with P0171. For most people, the first sign that something is wrong is the check engine light.

  • Mileage-it may or may not suffer depending on how much the air-fuel mixture has changed.
  • miss- If the air-fuel mixture is too far from the 14.7:1 sweet spot, it can cause your Toyota Verso to fail.
  • idle problems– With the air/fuel mixture changed, the vehicle may run erratically while the computer compensates for engine operation.

Causes of P0171 Toyota Verso

The P0171 code is thrown when something has caused too much air or not enough fuel. With that in mind, here is a list of the most common causes:

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Vacuum leaks

Your Verso's MAF and/or MAP sensors measure air as it enters the engine. If there is air leaking past the MAF sensor, it is not measured when it enters the intake, which increases the air to fuel ratio.

One of the most common causes for the P0171 code to appear is a vacuum leak.Listen and look around the engine compartment of your Toyota Verso to see if you can find the vacuum leak.

Look for any hoses or sensors connected to the intake manifold. Make sure they are not cracked and are firmly attached. Listen for unusual noises.

The YouTube video link is an amazing resourcehow to find a vacuum leak.

Oxygen sensor

The P0171 code is thrown when the bank an O2 sensor reports that your Verso's engine is running lean.

The sensor above or just after the exhaust manifold is usually the sensor that reports the lean condition. If it is faulty, it can cause a false P0171 code.

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exchange test

If your Verso has two cylinder banks, you can swap the O2 sensors on each side.

  1. Clear your passwords.
  2. Swap bank one sensor one oxygen sensor with its bank two sensor.
  3. Start the car and wait for the check engine light to come on.
  4. After pulling the codes if it changes to P0174, that is proof enough that a faulty O2 sensor was causing P0171 in your car.

Mass air flow (MAF) sensor.

The mass air flow sensor calculates the volume of air entering the engine. If it's faulty, your car's PCM won't know how much air is getting into the engine. When this happens, it can cause your Toyota Verso's engine to run rich or lean. If you got rich, you wouldP0172.

Cleaning the MAF or MAP sensor

Your Verso's MAF sensor is covered in tiny electrodes that can detect how much air is passing through it. Unfortunately, it cannot read the air properly if it is dirty.

Local parts stores sell special MAF sensor cleaners. If you use anything else to clean it, you risk damaging its delicate electronics.

fuel injector

P0171 indicates that your Toyota Verso is getting too much air or not enough fuel. A clogged or damaged fuel injector will cause the air-fuel mixture to run out in a particular cylinder. You may see a cylinder misfire code or a specific injector code with P0171.

If you have one or more faulty fuel injectors, the air/fuel mixture can leak.

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Fuel pressure regulator or fuel pump

With P0171, there is probably not enough gas getting into the combustion chambers. This can happen if the fuel pressure regulator is not allowing enough fuel to reach the fuel rail.

A faulty fuel pump behaves exactly the same way. The only way to find out why the fuel pressure is too low and is causing the P0171 in your Toyota Verso is to locate it from the fuel rail and see where the pressure starts to drop.

exhaust gas leak

An exhaust leak will change the amount of oxygen collected by the B1S1 O2 sensor. When this happens, it will report a false impossible condition. You will probably hear the exhaust leaking.

Air filter

Although not the most common reason for the P0171 code to appear, a clogged air filter can definitely cause it.

Possible fixes for P0171

Here are the steps you can follow to diagnose P0171 in your Toyota Verso.

  1. Check for other trouble codes. They will probably point out which part of your car is at fault.
  2. Listen for an exhaust leak or vacuum leak inside the engine. The exhaust leak should be near the B1S1 O2 sensor.
  3. Inspect all hoses connected to the intake manifold as well as the intake hose at the front of the throttle body.
  4. Check if the air filter is dirty.
  5. Check for leaks at the intake manifold gasket.
  6. Check the fuel pressure.
  7. Check the fuel setting on a quality scanner.

common questions

Is P0171 a malfunction hazard?

It is rare for a vehicle to break down on its own when the P0171 code is the only one. However, you don't want to ignore it. This could eventually damage your Verso catalytic converter.

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My Verse has P0171 and P0174 together. What does this mean?

If your Toyota Verso has P0171 and P0174 together, it rules out some issues and provides anecdotal evidence to narrow down the problem.

  • It's possible that the Verso's O2 sensors are working fine, as they both report that the car is low on charge.
  • A bad fuel injector will not cause a lean code to appear on BOTH sides of the engine so you can rule them out.
  • An exhaust leak is unlikely.
  • It leaves the MAF (or MAP) sensor, vacuum leak, air filter, or fuel pressure on the table as possible causes, as they would affect both sides of your Verso's engine equally.

Is P0171 hard to repair?

P0171 in Toyota Verso is not difficult to fix. On the other hand, it is difficult to diagnose. Searching for any other codes that appear with it can save you time.


How to fix fuel trim system lean bank 1? ›

A common fix is replacing the air-fuel sensor or the O2 sensor. However, replacing these parts may not solve the issue's root, since the code could be caused by a dirty or faulty mass airflow sensor or even vacuum leakage. The new O2 sensor may then be forced to read differently in an attempt to compensate for this.

What are the most common fixes for P0171? ›

You can usually fix P0171 using the following steps:
  • Replace the fuel pump or fuel filter.
  • Change the fuel pressure regulator.
  • Replace the powertrain control module.
  • Change one or more injectors.
  • Replace one or more oxygen sensors.
  • Change the mass airflow sensor.
  • Repair vacuum leak.

What does P0171 system too lean bank #1 mean? ›

What the P0171 code means. The P0171 OBD-II code means that, on the first bank of the engine, the fuel system is running weak or a vacuum leak exists near this side of the engine. A lean condition occurs when the engine either receives too little fuel or too much air.

Can a bad O2 sensor cause a P0171? ›

You probably know that the answer the questions is — no! A P0171 or P0174 lean code with an O2 sensor reading lean all the time mean — well, several things. The real problem may not be a bad O2 sensor, but possibly be an engine vacuum leak, low fuel pressure or dirty fuel injectors that are causing the engine run lean.

Can a loose gas cap cause P0171 code? ›

Causes can be leaks in the many rubber hoses in the air intake, leaking hoses from the secondary air pump, a fuel tank vent valve not sealing, a gas cap that isn't tight as you noted, and so on.

Is it OK to drive with P0171 code? ›

What Does Code P0171 Mean? Issue Severity: MODERATE– Extended driving with this code can cause internal engine damage. Repair Urgency: Get this code fixed as soon as possible to avoid damage to spark plugs, pistons, and catalytic converters.

What sensors can cause a lean condition? ›

Any sensor that measures fuel pressure or airflow can result in lean conditions. This includes the intake air temperature sensor, manifold air pressure sensor (MAP), and the EGR (exhaust gas recirculation) sensor.

Why does bank 1 and 2 run lean? ›

If you have codes stored in the engine computer for lean bank 1 and 2 is caused by the entire engine is running lean. This is caused by not enough fuel getting into the engine or too much unmetered air getting into the engine and the computer cannot compensate anymore to run it normal.

What are the symptoms of a lean run? ›

A lean running condition may manifest in driveability symptoms that have not (or not yet) triggered a DTC. Customer complaints may include symptoms such as decreased fuel economy, lack of power, hesitation on acceleration, backfiring through the intake, overheating, weird smells or other problems.

What causes a lean fuel mixture? ›

A lean fuel mixture occurs when there is too much air or not enough fuel in your engine. This can result in your car's engine not operating optimally. Since there isn't enough fuel being burnt, your car may stall, operate roughly or struggle to accelerate.

Can a bad catalytic converter cause a p0171 code? ›

This code is a crankshaft position sensor failure. It would have nothing to do with the catalytic converter. It can cause issues with starting the vehicle and keeping the engine running, which may have an effect on the exhaust system. A failing cat can also cause stalling, so without the code, they could look similar.

Can spark plugs cause P0171? ›

Not likely. A P0171 ( too lean, Bank 1 ) code is most often caused by a vacuum leak downstream from the MAF sensor or a malfunctioning MAF sensor. Bad spark plugs could actually cause the opposite code ( too rich, bank 1).

Can a clogged fuel filter cause P0171? ›

A failed fuel pressure sensor, pump, or clogged fuel filter can cause the P0171 trouble code.

How much does it cost to fix p0171? ›

You may get lucky with one of the simple repairs mentioned above. A broken vacuum hose sucking in air can be around $50, or a clogged fuel filter for $100. On the other hand, an oxygen sensor or mass air flow sensor can bring a bill of $400 to $500 dollars.

Will a vacuum leak cause a lean code? ›

A vacuum leak will cause the engine to run lean. In other words, there will be more air entering the engine than is needed to balance out the air/fuel ratio.

What does system Lean Bank 1 mean? ›

The OBDII trouble code P0171 - System Too Lean (Bank 1) means that the engine air-fuel mixture is too lean, or there is too much air and too little fuel. Driving a car with the code P0171 can cause more damage to the engine over time, as when the engine runs lean, the combustion temperature is higher.

What is the code for stuck lean? ›

P2195 is a Diagnostic Trouble Code that means “O2 Sensor Signal Stuck Lean Bank 1 Sensor 1”. This trouble code indicates an oxygen sensor issue.

What does system too lean at idle mean? ›

This code indicates that the system is too “lean,” which means that there's more air than expected and not enough fuel. More About the P2187 Code. This code doesn't trigger the first time there's an issue with the air/fuel mixture.

What are the symptoms of a vacuum leak? ›

Typically, a vacuum leak will cause situations like hard starting, rough idle, excessive fuel consumption, and engine codes. You might even be able to hear a leak - sometimes a whooshing or whistling sound can be heard with the engine running.

Will a bad fuel filter throw a code? ›

A clogged fuel filter will cause error codes. The ECM will throw a lean air-fuel mixture or misfire according to the trouble codes.

What causes P0171 and P0174 at the same time? ›

When your powertrain/engine control module receives a reading that indicates there's too much oxygen and the ratio is incorrect, it sends an error code P0171 or P0174. Depending on the problem, it may send both codes if the issue is causing a lean condition on both engine banks.

Can an air temperature sensor cause a P0171? ›

Tip : A faulty or skewed coolant temperature sensor and/or air temperature sensor can cause certain systems to mis-calculate air/fuel mixtures, resulting in P0171, P0174 DTCs.

Is P0171 expensive? ›

Running a diagnostic for a P0171 will usually cost you $75 to $150 per hour of labor. However, the cost to fix this issue will vary greatly depending on what the root issue is.

Can a bad downstream O2 sensor cause a lean code? ›

Yes the O2 sensor can cause the vehicle to run lean. What the O2 sensor does is read the amount of air entering the engine and sends that information to the computer, the computer reads this information and determines how much fuel the engine needs.

What do spark plugs look like when running lean? ›

If the engine is running to lean, the spark plug can look greyish white. If the engine is running to rich the spark plug will look black, sometimes a glossy black if it's really rich.

Can a bad coolant temp sensor cause lean code? ›

The coolant sensor may cause the engine to run the cooling fans at the wrong time if sensor is reading too high of temperature output. The engine may run extra rich or lean if the temperature output is not correct.

Can an exhaust leak cause p0171? ›

Absolutely, a leaking exhaust manifold can cause those codes. Those codes do NOT mean the O2 sensors are bad, it means a lean condition has been detected. Do not replace O2 sensors when you have those codes. Exhaust leaks can cause O2 sensors to read lean.

What are the symptoms of a lean fuel mixture? ›

A lean fuel mixture (too little fuel for the amount of air in the cylinder) can cause an engine to have a surge or miss at idle and part throttle, stumble on acceleration, engine overheating, cause a lack of power, and create possible engine failure from the lean air/fuel mixture.

Does running lean hurt an engine? ›

Yes, an engine running lean can certainly end up damaging itself. An engine that's designed to use a stoichiometric mixture will make less power when fed a lean mixture compared to its figure from when it was running a stoichiometric or rich mixture. An engine running lean can also lead to a 'soft seize'.

How do you check lean? ›

Lean body mass is your overall weight minus your weight from body fat. Basically, if you subtract the weight that comes from fat (your body fat percentage) from your total weight, you will have your lean body mass.

What are 2 things that can cause a lean mixture? ›

Alternatively, the causes for your engine running lean are likely one of the following:
  • A vacuum leak.
  • Faulty pump regulator.
  • Poor fuel pressure.
  • Insufficient fuel.
  • The EGR valve is stuck in the open position.

How do you adjust lean fuel mixture? ›

Technique: Leaning the mixture
  1. At altitude, set cruise power.
  2. Lean by reducing the mixture gradually until the engine runs a little rough. ...
  3. Slowly enrich the mixture until the engine smooths out.
Mar 1, 2017

How do you adjust lean mixture? ›

Things You Should Know

Bring your engine to a lean mixture by turning its screws a quarter-turn at a time, counter-clockwise. Then, slowly bring them back to equal. Tighten the idle adjustment screw to increase idling speed and loosen the screw to decrease idling speed.

How much does it cost to fix code P0171? ›

You may get lucky with one of the simple repairs mentioned above. A broken vacuum hose sucking in air can be around $50, or a clogged fuel filter for $100. On the other hand, an oxygen sensor or mass air flow sensor can bring a bill of $400 to $500 dollars.

Can a bad mass air flow sensor cause lean codes? ›

If you understand that a defective mass air flow (MAF) sensor can cause an extremely lean condition by underestimating the amount of air flowing into the engine, then you can understand how a defective MAF sensor can be mistaken for a defective fuel pump assembly.

Can spark plugs cause p0171? ›

Not likely. A P0171 ( too lean, Bank 1 ) code is most often caused by a vacuum leak downstream from the MAF sensor or a malfunctioning MAF sensor. Bad spark plugs could actually cause the opposite code ( too rich, bank 1).

Is it OK to drive with p0171 code? ›

What Does Code P0171 Mean? Issue Severity: MODERATE– Extended driving with this code can cause internal engine damage. Repair Urgency: Get this code fixed as soon as possible to avoid damage to spark plugs, pistons, and catalytic converters.

Which oxygen sensor is more important? ›

– the air/fuel ratio sensor provides a higher level of sensitivity than the traditional oxygen sensor. This allows the EMS to respond to the needs of the engine with higher accuracy, which enables the fuel to burn more efficiently, therefore producing lower emissions and increasing the vehicle's fuel economy.

What are the signs of a mass air flow sensor? ›

Six Signs My Car's Mass Airflow Sensor (MAF) Is Bad
  • Lean or Rich Fuel Mixture. ...
  • Difficulty Starting Your Car. ...
  • Engine Stalls After Starting or When Idling. ...
  • Engine Hesitation and Dragging. ...
  • Engine Hesitation and Jerking. ...
  • Engine Hiccups.
Apr 15, 2021

What are symptoms of a bad mass airflow sensor? ›

Stalling, jerking, or hesitation during acceleration

A bad MAF sensor can cause too much fuel to be left in the combustion chamber, creating untimed detonations. You'll experience this as poor drivability such as hesitations or sudden jerking motions, particularly during acceleration.


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