Fixing P0171 engine code for a Car

It can be one thing to buy a vehicle and another to maintain it. A check engine light is worrying, let alone a P0171 code that you don’t understand. Here we cover all the basics of fixing the P0171 engine code of a Chevy, Ford, Toyota, or Nissan, whichever vehicle you may have.


Fixing a P0171 engine code in a Chevy, Ford, & Toyota is done with a diagnostics car code reader to figure out why it’s giving you a “system too lean (bank 1)” code. The most common reasons for a P0171 code are a fuel pump issue and a faulty mass airflow sensor. The cost of fixing a P0171 engine code usually ranges between $100 and $1,700, depending on the issue.

In this article, we also go over the following:

  • The severity of the issue
  • Symptoms to look out for
  • Best ways to deal with the P0171 code

DIY steps to diagnose code P0171

There are simpler ways to diagnose this code without having to call a mechanic and spend extra bucks. Here are some products to help you out.

Car Code reader

Determine the cause of your engine light with this diagnostic tool. Its super-easy to use.

It can read and erase codes as well freeze frames. You can get engine speed, coolant temperature, calculated load value, and more. There is also no need for a charger or battery. The tool gets the current directly from your vehicle through the OBDII data link connector. The scanner is very much portable and has a 2.5 feet long cable.

BrandMOTOPOWER MP69033 Car OBD2 Scanner
Display resolution128 x 64
Item Dimensions LxWxH6.02 x 2.75 x 0.91 inches
Power SourceBattery Powered
Screen Size2.7 Inches
Special featureAcrylic screen cover


  • You’ll find very few devices at such a good price.
  • It works on cars built after 1996.
  • We love the value of the price point of this thing.
  • It gets the job done easily.


  • It’s not a high-end device.
  • A person with a 1998 car reported it not working as intended.
  • You can get a free reading at Autozone.
Code reader
Get this code reader.

Universal scanner

A trusted tool by more than 35000 customers, this scanner has it all. Recommended by popular YouTuber and mechanic Scotty Kilmer, it boasts exceptionally accurate and speedy results. The large screen and long cable are an asset, making it the professional’s first choice. Unlike other scanners, this is universal and compatible with OBDII protocols. The speed and accuracy are unmatched and thus rated 4.6 stars.

BrandANCEL AD310
Item Weight‎9.6 ounces
Package Dimensions‎9.17 x 6.34 x 1.42 inches
Power SourceBattery Powered
Screen Size1.4 Inches


  • It’s a much higher-end device.
  • It’s very versatile.
  • it’s a significant step up from the other two devices included.


  • It’s significantly more expensive.
It's very affordable.

New model Scan tool

It is a 5-year warranty tool that boasts of the airbag, ABS/SRS/Transmission diagnostic all in one. Apart from reading and erasing codes and viewing freeze frames, it has an:

  • O2 sensor test
  • an EVAP test of the fuel tank
  • and more

It even has live data graphing, a huge graphic screen, and a printing function for the best of experiences. It’s the perfect gift for any car owner so they can always stay on top of their vehicle’s needs.

Item Weight‎1.41 pounds
Product Dimensions‎9.06 x 1.77 x 7.8 inches


  • It’s even cheaper than the previously suggested product.
  • It’s good for a cheap OBD scanner.
  • It can reset codes.
  • It’s easy to use.


  • When testing it, we had some issues with the live data graphs menu.
  • You may have needs requiring you to invest in a more advanced unit.
  • A user received one with a cracked screen.
It's a step up.

How do I fix codes P0171 and P0174?

There are a couple of steps to follow to diagnose and fix both codes:

Figure out components

If both codes are showing at the same time, figure out which components are affected uniformly in both cylinders or banks. These components include the:

  • MAF sensor
  • a clogged fuel filter
  • and the fuel pressure regulator.

Use a scan tool

Using a diagnostic tool to find the source of the problem is certainly very handy. It can point to the oxygen, MAF sensors, or any other part that is the origin of the code.

Model issues

Sometimes the issue is particular to the vehicle itself. The Buick Encore and Honda CRV or Lexus will have their manuals and causes for a code. Check the manual and try to find the source of the issue.

Check the MAF and throttle body.

The MAF sensor is a very common problem but it can be tested easily. If your Nissan Altima, Honda Accord, or Subaru is flailing in engine power or idling roughly, you should check out the MAF sensor first. If you’re finding the fuel being used up quickly, clean the MAF sensor and consider replacing it if it still doesn’t work.

What does the code P0171 mean?

Its tricky business of knowing the answers to all the fault codes in the car system. But we’re here to help!

The P0171 code is triggered by the vehicle’s Power train control module, also known as PCM. The PCM is like the CPU of the car. It is the computerized control unit that is in charge of the transmission as well as the engine. Several sensors in and around the car are attached to it, like nerve endings in a brain.

The P0171 code is triggered due to the air and fuel ratio. When the oxygen level is too much, or the fuel is too low, the system is too lean. Thus the code triggers the PCM.

It could be that there is a vacuum leak causing this to happen or several other issues that are listed below.

Have you experienced any of the following symptoms?

  • A check engine light
  • Loss of power
  • Rough idle
  • Engine misfire
  • Hissing sound
2006 Toyota corolla CE Sedan 4D

What causes the problem?

These codes are caused by the engine running too lean or without much fuel. The only difference lies in their Bank, meaning which side of the engine the issue is. P0171 is triggered when Bank 1 or cylinder 1 is facing lean fuel, and P0174 is triggered when Bank 2 or cylinder no.2 is running lean.

Here are some of the reasons this could be happening:

Fuel pump issue

Just as it sounds, the job of a fuel pump is to deliver gas to the engine. The air-fuel ratio is distorted with too much air when it cannot do this. The fuel pump may need repairing or replacing if it is getting weak and causing the system to run lean. Don’t worry everything can be fixed!

Faulty Mass airflow sensor

If the mass air flow sensor is dirty or faulty, you will certainly get a reading of the P0171. The sensor’s job is to detect the airflow. If it’s too much, it will cause a lean system. But it may not be the case each time. Perhaps the sensor is faulty or dirty and not detecting the correct airflow. In this case, you may need to replace it.

Vacuum leak

Usually, the air intake occurs through the throttle body of the car. The vacuum pump works tirelessly to balance the air-fuel ratio. When there is a vacuum leak, this intake is increased and disrupts the fuel mixture and thus the combustion process.

PCM issues

Issues with the control system or the PCM can also cause a faulty reading. The PCM should be checked and repaired, so the check engine light doesn’t stay on for no reason.

Dirty fuel injectors

Fuel injectors have a great function to play in the car. There are plenty of signs that indicate a clogged injector. Not only does the air-fuel mixture get distorted but also the mileage starts to fall by a significant factor.

It can also cause the RPM needle to wave about even when you’re not changing gears. Rough idling and misfires are also common signs to watch out for.

2013 Cadillac ats 2.0L Turbo Premium Sedan 4D

Catalytic converter blocked

The converter’s job is to break down the harmful compounds into harmless ones for release into the air through the exhaust pipe. When this gets clogged, it’s even more likely that polluted air will stay inside and sway the fuel mixture.

Clogged fuel filter

The role of a fuel filter is to allow the fuel to get filtered for any debris, dirt, or foreign particles that can potentially disrupt the working of the injector. When this gets clogged or stops working, there will be issues with the overall fuel quality of the engine.

Faulty sensors

There are many sensors in a car and all have a different role to play. It’s the sensors that trigger the PCM for the codes. If the sensors are faulty, they are going to display wrong readings and thus cause the driver to believe that the engine has problems. In this case, the sensors will need repair or replacement to deliver the correct reading of the level of oxygen intake.


If you’re driving a Chevy Silverado, or a Chevy Cruze, having a P0171 code might bother you at some point. What it means to have this is that your system is running lean or there is a vacuum leak. Both scenarios have the same possibility of insufficient fuel reaching the pump. The air-to-gas ratio is much too high, and thus the car must also be powering less.


If your car is a Toyota Corolla or any Toyota, a P0171 means something slightly different. It indicates that the MAF or mass airflow sensor is faulty or detecting too much air in the tank. There could also be a vacuum leak in the valve of the MAF sensor. It could also be a sign that an oxygen sensor has gone faulty.


In a Ford, like a Ford F150 or Ford Ranger, the code indicates the first bank of the engine is weak. The weak engine is causing too much oxygen or too little fuel in the mix. There could also be a potential vacuum leak in the valve. The fuel pump could be weak, or the MAF sensor could be dirty. It causes the code to occur.

How easy is it to diagnose?

2002 Toyota corolla Le

It can be relatively moderate to easy for someone with experience to diagnose the problem. A mechanic can simply use a vacuum gauge to detect the leak in the engine. A hissing sound will already be present in this case. Other diagnosis methods include checking the:

  • catalytic converter
  • MAF sensor
  • oxygen sensor
  • and fuel pump and filter checked out thoroughly.

It is easy to diagnose as long as it is done on time. If it is not repaired on time, the car will start to lose power and idle with vibrations.

Will a P0171 code clear itself?

It is highly unlikely. Unless there is a fault in the PMC, there are slim chances that the code will clear itself until some steps are taken. Some parts must be cleaned, repaired, or even repaired before the code clears itself. Even manually, you will need a scan tool to view and clear the code.

You will probably need to check and replace the fuel filter, fuel pump, or fuel injector to get the code to go away. The catalytic converter must also be checked.

How much does it cost to fix?

Each component has a different price and thus can be a huge range of costs for the fix.

  • Vacuum leak – the vacuum leak can be found with a gauge and will be fixed in a range of $100-200.
  • A fuel pump – A fuel pump can be weak and cause less amount of fuel in the mix. It can cost between $1300-$1700 for the replacement as it is the main component.
  • Oxygen sensor – an oxygen sensor can also go wrong and cause you between $200 and $300 for the replacement.
  • A fuel pressure regulator will cost between $200 to $400 for the replacement.
  • MAF sensor replacement will cost around $300 to $350.

How serious is the issue?

It is to be taken seriously, certainly. No doubt driving around without fixing the P0171 code can result in power issues and engine performance problems. It eventually leads to damage to parts like the catalytic converter, which is in charge of converting the harmful gases into broken harmless compounds for release.

If the air-to-fuel ratio is high, you look at poor performance during acceleration or incline. You should certainly treat it as soon as possible.

Symptoms to look out for

Before you land up in such a mess that you don’t know where to start fixing, it’s a good idea to check for these symptoms.

A check engine light

The check engine light is one of the first indicators of something gone wrong. Although it will puzzle you about which component to check, combined with other symptoms listed below, it will be pretty obvious as the P0171 code.

Loss of power

It could be a major sign if you’re experiencing a sudden loss of power when you try to speed up or drive uphill. When you press down on the gas, and there’s less fuel and more air in the engine, this results in no effect and instead a slowing down of the vehicle.

Rough idle

You’re at a stop light or in the driveway, and the vehicle is shaking badly. It is a sign something is up with the engine. Take a look at the PCM and check for the codes.

Engine misfire

If your engine is sputtering and spitting noticeably, open it up for a good look. A misfire can sound like a bullet going off and it’s not a sound one can miss.

2006 Toyota corolla CE Sedan 4D from above

Hissing sound

Unusual sounds in a car can mean several things. If you’re familiar with gas leaks, you can detect a hissing sound near the vacuum where it might be leaking and causing too much air.

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