Lean Nissan: Code P0171 – Meanings, Causes And Solutions

Lean Nissan or code P0171 is a common problem that most Nissan owners face. But what does it mean and what causes it?

Code P0171 or system too lean means the air-fuel ratio is incorrect, and the system cannot compensate. The most common causes are vacuum leaks and faulty or damaged engine monitoring sensors.

Read on as we get into details of the causes, symptoms, and how to fix P0171 on Nissan vehicles.

What Is Code P0171 On Nissan?

Code P0171 or system too lean error means that there is too much air and too little fuel in bank 1.

The correct air-fuel mixture ratio is 14.7:1. Once there is too much air, the powertrain control module (PCM) tries to compensate by injecting too much fuel. If this condition escalates, the OBD2 error code P0172 becomes active, and the Check Engine Light comes on.

The OBD2 code P0171 requires immediate attention. Driving long distances with it can cause servere engine damages, and the most affected components are spark plugs, pistons, and catalytic converters. Therefore, you need to diagnose and fix the problem at the first opportunity.


The following are the most common signs of the P0171 code:

Check Engine Light Is On Or Flashing

Check Engine Light is the first warning sign when the code P0171 is active. PCM constantly monitors the air-fuel mixture ratio. If there are prolonged discrepancies, it sets the code, and the check engine light comes on or flashes. Using an OBD2 scanner can also help you find code P0171.

Loss Of Power From The Engine

There can be a sudden loss of power when the code P0171 is active. That is because of engine misfiring or not enough fuel in the mixture for combustion in the cylinders. The vehicle will feel sluggish to accelerate or go uphill due to insufficient power. Your engine can even stall at a stop sign when running too lean on bank 1.

Rough Idle

An incorrect air-fuel ratio in the engine block will cause engine troubles, and make your engine run roughly. In some cases, the engine may fail to start. And if it does, it experiences rough idle due to misfiring.

White Deposits At The Tip Of Spark Plugs

If you continue driving your car with code P0171, the most common consequence is the burned plugs. This can appear as blisters on the insulator tips or white deposits. The reason is usually a too lean air-fuel mixture, loose spark plugs, incorrect ignition timing, or engine overheating.

Hissing Sound From The Engine

A vacuum leak is the most common cause of code P0171. If that is the case, you may hear a hissing sound coming from the engine block.

Possible Causes

There is a long list of causes of code P0171 or system too lean problem on Nissan cars. These include, but are not limited to:

Disconnected Or Leaking Hoses

If you get the P0171 code, the first thing to check is the disconnected or leaking hoses that can cause uncontrolled engine air intake. A whistling or hissing sound is a possible confirmation that your car is suffering from a vacuum leak. Inspect the air intake hose and disconnect or open the hose underneath the engine.

Faulty Airflow Sensor Or Air Filter

Debris such as leaves that found their way through can block mass air flow sensors. Also, in case the sensor is faulty, it will give incorrect data. Your air filter may also be blocked by debris or has visible holes that let in more air than necessary.

Damage Engine Intake Components

Damaged, disconnected, or unsealed engine intake parts such as gaskets and purge valve seals can also cause incorrect air-fuel mixture. Check them for possible leaks and cracks. When your engine is sounding rough, the purge valve seal may be the culprit.

Faulty Oxygen Sensor

The oxygen sensor monitors the oxygen level in the incoming air-fuel mixture and exhaust. If it detects a significant amount in the exhaust gasses, it sends a signal to the PCM that triggers the P0171 code. And once the sensors become faulty, they can also send incorrect information that causes the computer to set the error code.

The code P0171 can also result from other engine monitoring sensors. When diagnosing this problem, check all possible causes.

How To Diagnose This Code?

The diagnosis of code P0171 is procedural. You don’t want to skip any step and replace components in perfect working conditions. Proceed as follows:

Step 1: Scan The Vehicle For Stored Code

The first step is to use a compatible OBD2 scanner to read the stored error code. Ensure it is only P0171 and not any other. If you find another fault code apart from P0171, address it first before proceeding to the second step.

Step 2: Inspect Vacuum Lines

Since vacuum leak is the most common cause of P0171 code, start by inspecting all hoses for leaks or disconnections. Ensure no visible damages or cracks before moving to the third step.

Step 3: Check Mass Air Flow Sensor

Remove and clean the mass air flow sensor using an appropriate cleaner and inspect for any problems. Fix it back if it looks fine.

Step 4: Check Components Of The Exhaust System 

Faulty or leaking exhaust components also cause the problem. Inspect them if you can spot any dark substances close to any possible leaks or cracks.

Step 5: Inspect Fuel Pressure

When the fuel system cannot supply fuel at the required rate, the system will run lean. Inspect fuel pump and fuel injectors, ensuring everything is functioning correctly. Use a fuel pressure gauge to ensure enough gasoline passes to the engine block. Replace faulty components and clean any clogged parts that may hinder fuel flow as necessary.

Step 6: Inspect Spark Plugs

Burned spark plugs usually have white deposits at the tip. Check and replace them when needed.

Step 7: Replace Air-fuel And Oxygen Sensor

A faulty air-fuel mixture sensor or oxygen sensor should be the last fix to clear the error. If the Check Engine Light is still on, run the diagnostic test on these sensors and replace them. Contact your mechanic for a further diagnosis when nothing works.  

How Much Does It Cost To Fix P0171 Nissan Lean Problem?

The cost of fixing the P0171 error depends on the labor cost for diagnosing it and components that require replacement. Typically, repair shops charge $75-$150 for diagnosis. You should get a detailed sheet outlining additional costs to fix it.

The following chart shows the estimated costs of replacing or repairing different parts when fixing the P0171 problem.

ComponentCost ($)
Vacuum leak$100-$200
Clean MAF$100
Replace MAF$300
Fuel Pump$1300-$1700
Fuel pressure regulator $200-$400$200-$400
Exhaust repair$100-$200
Air fuel sensor or oxygen sensor$200-$300


P0171 code requires immediate attention. Address it on time to prevent damages to other engine components following the steps outlined in this article or contact your mechanic. Failure to fix the error will result in rough idling, engine stalling, loss of engine power, and misfiring. You should, therefore, act on time.

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