P0171 OBD2 Trouble Code – Clean the MAF and check O2 sensors!

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P0171 OBD2 Trouble Code


Meaning of P0171 Generic OBD2 Trouble Code

The technical definition of P0171 code is: System Too Lean in Bank 1

This means the engine – specifically in bank 1 – is running lean (similar to code P0174). It is either the engine is receiving too little fuel or possibly too much air, hence resulting in an overly lean running condition.

Pro Tip
P0171 OBD2 Trouble Code is sometimes tricky to diagnose but I suggest start by cleaning or replacing your MAF, checking the air filter, and also checking your fuel filter. Next to check is the front O2 sensor. If those all look good you may have a vacuum leak or exhaust leak and should run a smoke test!

The P0171 generic OBD2 DTC is usually triggered by the front O2 sensor, or oxygen sensor #1 (similar to P0135). Once the ECU detects the sensor is detecting too much oxygen in the exhaust, it will try to compensate by maintaining the ideal burn ratio of 14.7 Air to 1 Fuel. If the ECU is unable to maintain this ration, it will trigger a check engine light (MIL) and display a P0171 code on your OBD2 scanner.

What are the causes of P0171 OBD-II code?

The possible causes of a P0171 generic fault code are many! Here’s the most common causes of the P0171 DTC that we’ve encountered:

  • Dirty or faulty Mass Airflow Sensor (MAF)
  • Dirty or faulty Oxygen O2 sensor
  • Clogged fuel filter
  • Vacuum leak

The first thing to check is the air filter or air cleaner element. If the filter is clogged or excessively dirty, this is enough to impede or restrict the air flow, hence resulting in a lean running condition.

Besides a dirty air filter, the P0171 code can also be blamed on a dirty or faulty MAF sensor and a clogged fuel filter. Cleaning the MAF with some brake cleaner should help isolate or rule this one out.

maf cleaning
Clean your dirty MAF! Img creds: FamilyHandyMan

The code can also be attributed to a faulty or stuck PCV valve. In some cases, the trouble code is also triggered by a sticky or failing fuel injector. If the motor is not getting enough fuel, the trouble code can also be blamed on a plugged or dirty fuel filter.

But in some cases, it can also mean the existence of a vacuum leak in the MAF sensor or PCV connections. The bad news is diagnosing a vacuum leak is tricky without using specialized tools like a Smoke Tester. There are also times when the fault is caused by a faulty O2 sensor as well.

P0171 fault code DTC explained

What are the symptoms of P0171 DTC?

The most obvious symptom is the presence of a check engine light in the dash. This is followed by engine problems such as engine knock during hard acceleration, rough or problematic idling, hesitation or surging, and a general lack of performance.

  • Check engine light (MIL)
  • Slow throttle response
  • Rough idle
  • Many others
This is box title

P0135P0141, P0171P0172, P0174 are all common to see if you have Sensor issues!


How much does it cost to fix P0171 Fault?

The cost will depend on the source of the problem. And unfortunately because of the nature of this code, you’ll spend some time isolating the problem.

The first thing to do is to replace or clean the air filter and fuel filter. While you’re at it, you should also check the MAF sensor. If the sensor is dirty, clean it using a sensor cleaner. In most cases, cleaning the air filter and MAF sensor is enough to solve the problem. But if the MAF sensor if faulty or damaged, you need to spend around $40 to $80 for the sensor alone, after labor costs you could be looking at $150.

If that still doesn’t solve the problem, you want to check for vacuum or exhaust leaks. This is the part that sucks. 

Since the P0171 DTC can be caused by a variety of faults, it is important to follow the proper diagnostic procedures. Replacing the fuel filter and air filter will set you back $30 to $50 each plus labor. If the problem is caused by a vacuum leak (due to a broken or cracked rubber hose), the repair bill could be lower.


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