The P0171 Error Code : Symptoms – Causes and Solutions

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The P0171 Error Code : Symptoms – Causes and Solutions. Dealing with engine difficulties is one of the most aggravating aspects of car ownership. The engine is a vehicle’s lifeblood, and any problems with it must be addressed immediately. The dreaded P0171 code is a typical diagnostic problem code (DTC) that engines might have. The P0171 error number means “System Too Lean (Bank 1)” and signals a significant problem with your engine. In this post, we’ll go over what the P0171 code means, how it affects your engine, related codes, frequent symptoms and causes, and how to diagnose and eventually fix the problem.

The P0171 Error Code : Symptoms - Causes and Solutions

DTC P0171 Code Details

As previously indicated, the P0171 code denotes “System Too Lean (Bank 1),” which suggests your engine is having difficulty measuring the correct air-to-fuel ratio. Before we go any further, let’s define your air-to-fuel ratio and why it’s critical that it’s proper.

All engines have an ideal air-to-fuel ratio, commonly known as AFR, which is crucial for their smooth operation. The correct AFR while driving around at modest engine loads for the great majority of gasoline-powered street automobiles is 14.7:1, which means 14.7 parts air to 1 part fuel (gas).

A 14.7:1 AFR is totally stoichiometric at low loads, which means it provides a perfect blend of air and fuel for a flawlessly complete burn. Anything beyond 15.7:1 is considered lean, while anything below is considered rich. Low fuel blends contain less fuel, whilst rich fuel mixtures include more gasoline.

There are occasions when you want a richer fuel mixture, usually to boost performance, and others when you want a leaner mixture, usually to enhance fuel economy. However, for normal cruising, a 14.7:1 AFR is usually adequate for gas mileage and engine health.

You may be asking why we chose a ratio of 14.7:1. It’s not merely a number at random. Our engines use oxygen sensors to ensure that our AFR is set correctly. When those oxygen sensors are converted to the gas scale, a stoichiometric value of 1 corresponds to a 14.7:1 ratio on the gas scale. Different fuels have varying ratios, but gasoline has a 14.7:1 ratio.

What is the significance of my AFR?

The air-to-fuel ratio is critical because it guarantees that your engine operates at peak efficiency and health. Overly rich fuel mixes can cause poor fuel economy, premature spark plug wear, ringland failure, and lower performance. Low fuel mixes frequently cause engine detonation and pre-ignition. Detonation and pre-ignition are both major concerns that can result in catastrophic engine failure.

Detonation occurs after the spark plug has fired during the combustion process. It is a condition in which cylinder pressures rise as a result of extreme heat, potentially causing damage to the piston crown and ringlands. Pre-ignition is similar, but it happens before the spark plug fires. While the piston is rising up during the compression stroke during pre-ignition, the mixture suddenly ignites, spiking cylinder pressures once more.

Excessive cylinder pressures can cause severe engine damage. Pre-ignition is far more hazardous than detonation, yet both can be disastrous. For a more in-depth discussion of detonation and pre-ignition, visit Edge Autosport’s blog.

What does the P0171 error code indicate?

Therefore we now know that maintaining the proper air-to-fuel ratio (AFR) is critical. We also now understand that lean fuel mixes can harm the engine by generating pre-ignition and detonation. So, what does this have to do with the P0171 code?

The P0171 code means your “System Too Lean (Bank 1),” which means your engine has detected a low AFR. Although while your engine is continuously attempting to achieve its optimal AFR, this does not always occur in the real world because drivers are continually manipulating the throttle pedal. To get the best AFR, your engine is continually adding or withdrawing gasoline based on the reading from your car’s oxygen sensor. This is referred to as closed loop fuelling. The ECU uses the O2 sensor reading to adjust fueling to keep the AFR as close to 14.7:1 as possible.

Fuel trims are used by your engine to maximize AFR. Positive fuel trims indicate that fuel is being added, whereas negative fuel trims indicate that fuel is being removed. They are typically given as a percentage. Fuel trims of 1-3% are standard for autos that run smoothly. Fuel trims on cars with leaks in the intake system can reach 30-40% or even higher. To get the best fuel economy and engine efficiency, you want the lowest feasible fuel trims.

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If the P0171 error appears, it implies that your engine’s AFR is excessively lean and the engine is unable to adapt enough through fuel cuts. This usually signifies that your fuel trims have beyond the 25-30% range and your car is struggling to run effectively.

What does the P0171 code mean by Bank one?

This can be perplexing, but most modern engines have at least two cylinder banks. Bank 1 on a V-style engine refers to the side of the block containing the number one cylinder. It’s a little different on an inline engine. Because an inline engine has no left and right sides, bank 1 refers to half of the cylinders (on a 2 bank engine). Bank 1 is typically the first half of the cylinders (i.e. 1, 2, 3), and bank 2 is the second half (i.e. 4, 5, 6). Some 4-cylinder engines have only one bank.

The goal of having two banks is to allow for more exact fueling and to assist you narrow down the location of any potential problems. Most car owner’s manuals feature a schematic of the engine arrangement showing which side is bank 1, making it simple to check up.

The most common causes of P0171

The following are the most typical reasons of the P0171 error code:

  • Intakes from the aftermarket
  • Clogged/broken fuel injector
  • Fuel pump or fuel pump sensor failure
  • Fuel pump regulator failure/weakness
  • There is a vacuum leak in the intake system.
  • Oxygen sensor failure or contamination
  • Mass airflow sensor failure or contamination (MAF)
  • Exhaust dripping

The P0171 engine error code can have a variety of causes. Fueling system issues are one possible reason of the P0171 code. If your injectors, fuel pump, or fuel pressure regulator are clogged, faulty, or failing as a result of wear and mileage, they may struggle to give the necessary amount of gasoline. Lean AFRs can also be caused by vacuum leaks. Vacuum leaks are holes in the intake tract that allow air to escape or enter. With most vacuum leaks, unaccounted for fresh air enters the engine, resulting in a lean situation.

Other typical causes are malfunctioning oxygen sensors and unclean or faulty MAF sensors. If the oxygen sensor is old or broken, it can send inaccurate data to the engine control module (ECU), leading in a P0171 code. Furthermore, if your MAF is damaged, unclean, or malfunctioning, it may struggle to effectively estimate the amount of air entering the intake. As a result, the ECU may not inject enough fuel since it believes there will be less air, resulting in a lean mixture.

Finally, an exhaust leak is a common cause of the P0171 DTC. Exhaust leaks can cause your oxygen sensor to produce incorrect readings that cannot be adjusted for, resulting in the P0171 code.

Aftermarket intakes and the P0171 code

The usage of aftermarket intakes, such as cold air intakes, is one of the more typical reasons of the P0171 code. While these are terrific power adders for some cars and have been widely covered, they frequently require extra ECU tune to work well. Without tune, slapping an aftermarket intake on a MAF-based system is a prescription for disaster.

MAFs, or mass airflow meters, monitor the amount of air moving through the intake, into the manifold, and into the engine. It does so based on calculations based on the measurements and size of the stock intake. When you install aftermarket intakes, the MAF calibration is skewed because they are larger than stock and have different dimensions. A tuner can modify your MAF scaling with ECU tuning to compensate adequately. Without tune, you’ll frequently notice a lean code because unmetered air enters the engine and your fuel trims can’t account for it.

Another issue with aftermarket intakes is the usage of oiled filters. Excess oil frequently leaks out of the filter and into the MAF, causing erroneous readings. If enough oil leaks in and skews the readings, this can eventually result in a P0171 designation.

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Common Symptoms of the P0171 Code

The following are the most prevalent P0171 code symptoms:

  • Check Engine Light Is On or Flashing
  • Idle time
  • Power decline
  • The vehicle has been placed in limp mode.
  • Missing or clogged spark plugs
  • The engine will not start.
  • Pre-ignition and Detonation
  • Failure of the catalytic converter

If you have an issue with the P0171 code, it is likely that something is wrong with your engine. Your engine will struggle to operate and idle because it is unable to properly inject enough fuel. A lack of gasoline will result in a rough idle, power loss, and poor overall drivability. If your car has problems driving for an extended period of time, it may enter limp mode. This effectively disables the vehicle, reducing power and limiting speed.

The P0171 code will most likely illuminate your check engine light, and it may even flash repeatedly. As previously stated, lean fuel mixes frequently cause detonation and pre-ignition, which can result in catastrophic engine failure. Pre-ignition can also cause spark plugs to foul early or to develop white deposits on them.

If the condition persists for an extended period of time, the catalytic converter may fail. Normally, your engine would start before the cat, however this has happened to certain people.

P0171 Codes Related

  • P0170 Fuel Trim Failure (Bank 1)
  • P0172 System Excessive (Bank 1)
  • P0173 Fuel Trim Failure (Bank 2)
  • P0174 System Is Too Sparse (Bank 2)
  • P0175 System Excessive (Bank 2)

There are multiple codes associated with the P0171 DTC, and several of them will appear concurrently. One of the most common is P0170 “Fuel Trim Malfunction (Bank 1),” which refers to the fuel trims we discussed before and indicates that they have exceeded the 30% barrier in bank 1.

P0172 is quite similar to P0171, however it indicates that the engine senses a rich fuel mixture that it cannot correct for rather than a lean one. P0173, P0174, and P0175 are all the same code except for the cylinder bank. As previously stated, this allows you to narrow down the likely source of the problem by isolating half of the engine’s cylinders.

Code Severity Level P0171

Level: Very High – This must be addressed quickly.

Because of the potential of pre-ignition and explosion, it is critical that you fix this code as soon as possible. When using this code, do not drive aggressively or spiritedly, as this can cause major engine problems.

While your car is at low loads, it uses closed loop fueling, as we discussed. Yet, most cars use open loop fuelling when operating under high loads, such as when driving with the throttle wide open. While in open loop fuelling, your vehicle cannot correct for lean circumstances. This increases the likelihood of detonation and pre-ignition during spirited driving with the P0171 code.

The greater the engine load, the greater the risk of pre-ignition and detonation. Under high loads, detonation and pre-ignition frequently result in catastrophic engine failure.

Repairing the P0171 Error Code

Verify the P0171 Code

So, how do you resolve the P0171 error code? Because there are so many possible possibilities, this remedy is partly trial and error. Before proceeding with any fixes, ensure that you are dealing with the P0171 code explicitly.

Remove your aftermarket intake and inspect it for leaks.

If you have an aftermarket intake that is not tuned for, remove it immediately after confirming the right code and reset the codes. If the code does not return, the issue was caused by your aftermarket intake and will require specific tuning to be resolved.

And if you have the stock intake, a good place to start looking for vacuum leaks is in the intake tract. A smoke test is the most convenient way to accomplish this. Further information on how to smoke test your car may be found here. If you discover a vacuum leak, correct it and reset the codes. If you do have a leak, this is most likely the source of the problem. Check your exhaust header connections as well to determine if there is a leak there.

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Your sensors should be cleaned and tested.

If the code returns, the next step is to verify your MAF and fuel pressure sensors. Replace the faulty one and clear the codes if necessary. If they continue to return, the issue may be with your oxygen or O2 sensor. Clear the codes and replace the sensor.

Examine your fueling system.

If the errors persist after you’ve eliminated the MAF, fuel pressure sensor, vacuum and exhaust leaks, and an aftermarket intake, the issue is most likely with your fueling system. At this point, check your injectors on bank 1 to determine if any are clogged, as well as your fuel pressure regulator, if you have one. If these are satisfactory, the issue may be with your gasoline pump. You can check the voltage on your fuel pump to see whether it is working properly, and if not, replace it.

You should have been able to resolve your P0171 DTC code after following this step-by-step guide. Bear in mind that these are merely the most prevalent solutions. Your vehicle most certainly includes several other tiny sensors that could be the source of the problem. If you are unable to diagnose the problem using the techniques outlined above, you may need to consult with a professional mechanic.

P0171 Costs of Diagnosis and Repair

This is a serious yet reasonably inexpensive fix. Depending on the repair, you should expect to pay between $0 and $150 to complete it yourself. The majority of MAF, fuel pressure, and other sensors cost less than $100. Keep in mind that OEM parts are more expensive than generic replacements, and we normally advocate OEM.

If you have a shop fix the problem, you should budget for 1-2 hours of labor. Depending on your area, it is normally around $125 per hour.

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FAQ for the P0171 Code

What does the P0171 DTC indicate?

The P0171 DTC code signifies “System Too Lean (Bank 1),” which implies your engine has detected a lean air-to-fuel ratio that it cannot correct for. With greater engine loads, lean air to fuel ratios can be extremely harmful to your engine.

What kind of harm can the P0171 DTC do?

A lean air-to-fuel ratio can cause pre-ignition and detonation, both of which, if severe enough, can lead to catastrophic engine failure. You can also blow out your spark plugs or cause white deposits to form on them.

How much does it cost to repair the P0171DTC?

Depending on the nature of the problem and how long it takes to resolve, you will most likely be out $0 – $150, with the majority of the money going toward the cost of the replacement part. If you need a professional to diagnose and repair the problem, expect to pay between $125 and $250 in labor fees.

Can I drive if the P0171 DTC is present?

While you can still drive, you should not do so until it has been properly repaired. Lean fuel mixes are engine killers that can easily cause catastrophic damage. Under no circumstances should you attempt to run under higher loads, such as going wide open throttle, since you could cause catastrophic damage or put your automobile in limp mode.