Imagine your morning was going swimmingly, and you were on your way to work on time. But then you tried to start your car and found that your check engine light was on and the engine was running rough. Bummer! So then you pulled out your trusty OBD II scan tool and discovered that your vehicle had a P0171 code. Has this happened to you? Why did this happen, and what can you do to fix it?
A Code P0171 or system too lean bank 1 means too much oxygen or not enough fuel in the exhaust. This is a ‘lean’ condition or a ‘low fuel trim’ code. The P0171 OBD-II code indicates that the fuel system on the first bank of the engine is weak or that a vacuum leak exists on this side of the engine. The engine is in a lean state when it receives either too little or too much fuel.
The upstream oxygen sensor for engine bank 1 triggers the P0171 code, while the upstream oxygen sensor for engine bank 2 triggers the P0174 code.
The most common reason for the P0171 engine code is that the combustion system fills up with unmetered air. The air enters because of weak fuel pumps or dirty or defective mass airflow sensors.
Some other possible causes of a P0171 code are:
- Vacuum leak
- Weak fuel pump
- Broken fuel pressure regulator
- Blocked fuel filter
- Faulty powertrain control module
- Defective injectors
- Faulty oxygen sensors
- Clogged catalytic converter
Symptoms of P0171 include:
- Check Engine Light is on or flashing
- Loss of power
- Rough at idle
- Misfiring or “coughing” engine
- White spark plug tips
Cost to fix a P0171 code
When you take your car to a mechanic for diagnosis, most will begin with an hour of labor diagnosing your specific issue. Depending on the shop’s labor rate, this usually costs between $80 and $150. Then, if you have them carry out repairs, many businesses will apply this diagnosis cost to the required repairs. The shop will then give you an accurate repair quotation to fix your P0171 issue.
The code ideally results in the engine running poorly, which the driver will notice as a high idle, a misfire, a loss of power, or even engine stalling. All these can occur even before the check engine light illuminates.
Repair estimates for P0171
You may need to make one or more repairs to fix the problem related to error number P0171. The estimated repair cost includes both the parts you need and the labor to do the work.
- Vacuum leak fix: $100-$200
- MAF replacement: $300.
- Fuel pump: $1300-$1700
- Fuel pressure regulator: $200-$400
- Repairing an exhaust: $100 to $200 (if welded to repair)
- Oxygen sensor: $200-$300
Diagnosing P0171
Assuming no other fault codes are present, a mechanic can diagnose the P0171 using a vacuum gauge to examine the engine for any suction leaks.
- A vacuum leak makes a hissing sound, normally only audible when the engine is shut off.
- A fuel pressure gauge is also used to inspect the fuel pressure sensor and the MAF sensor (mass airflow).
- The engine’s vacuum and fuel pressure must be within the manufacturer’s standards to maintain a correct air/fuel ratio. Therefore, these two checks will usually determine the source of this error code.
- If the reason is still unknown after the mechanic has done these two checks, the problem is most likely with a sensor.
- The mechanic would then use the manufacturer’s technique to test the mass airflow and oxygen sensors.
- If all of these tests are completed and no problems are detected, the issue is most likely with the powertrain control module.
Common errors in P0171 code diagnosis
A common mistake is failing to look at technical service bulletins for your car model that may be relevant to this issue. You can check the NHTSA website to find out if your vehicle has any recalls or technical service bulletins (TSBs). Although not every issue code is associated with a technical service bulletin, double-checking is always a good idea, as it can save you time and effort.
