Diagnostic Trouble Codes: P0171 & P0174
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Today we’re discussing a common code that might show up when using your wifi OBD2 diagnostic tool, or bluetooth OBDII scanner. The P0171 or P0171 means that something is amiss with your oxygen sensor and can cause a variety of issues. Let’s dive into this code.
Pulling a P0171 or P0171 diagnostic trouble code is a common result when diagnosing a check engine light. The P0171 code is a standard code in all vehicles manufactured since 1996 from all manufacturers. The code or check engine light usually means that an oxygen sensor has detected a high amount of oxygen in the exhaust, also known as “running lean.” There may be no noticeable drivability symptoms as a result of this code. If there are drivability issues they would likely show as a rough idle, spark knock, or lack of power when accelerating.
What causes the P0171 DTC?
What causes P0171 codes? Unfortunately, if you were looking for a quick answer, there isn’t one in this case. The following issues could cause a P0171 or OBD-ii trouble code:
- Faulty or dirty Mass Air Flow sensor (MAF)
- Vacuum leak downstream of MAF sensor
- Faulty PCV valve
- Faulty camshaft position
- Crack in vacuum or PCV line (vacuum leak)
- Faulty oxygen sensor
- Low fuel pressure, lean bank or other lean condition
- Failed fuel injector
- Faulty control module or fault codes
- Exhaust leak or faulty intake manifold
- Outdated PCM software or faulty code reader
As you can see, there’s no one problem that causes a P0171 code to show. Some of the above issues are not simple repairs, but some are. If you’re lucky then you won’t have to spend too much time and money on fixing the issue.
Where to start
A great place to start in fixing a P0171 code is to take a look at the MAF sensor. Sometimes a quick cleaning of the sensor can resolve the issue. While it isn’t a guarantee that’s what the problem is, it’s the easiest place to start and could save a lot of work. If you have cleaned the sensor and the code resolves but returns, it could mean that the sensor is faulty and needs to be replaced. Cleaning and changing the air filter regularly will help protect the MAF sensor.
The next thing to check is the vacuum and PCV hoses. Any cracks or leaks would potentially cause a P0171 code. Ensure all connections are tight. If there are any cracks or leaks then that could be the issue causing the vehicle to throw a P0171 code.
It would also be advisable to check and see if there are any PCM software updates available. That could be a quick and simple repair.
The air intake is another place to check. Any loose connections or cracks could cause a problem. As you can see, air flow seems to be a theme here so far. Hopefully, if you have reached this point, you have found a simple hose that can be repaired or replaced without having to go any further. If not, things get slightly more complex from here.
If all vacuum, PCV, and air intake lines seem undamaged then another issue could be with fuel injection or pressure. Inspect the intake manifold gaskets. If there is any leakage, that would be enough to cause a P0171 code. You will also want to inspect the fuel filter. If it’s dirty then it could be causing low fuel pressure.
Unfortunately, it’s impossible to point to any single issue or solution for resolving a P0171 code. If you’re trying to fix this error, start with the simplest solution and move forward from there. If you’re lucky, a simple sensor cleaning is all you need.
Driving with this error code is not advisable. If a vehicle is running lean then it means that additional pollution is being put into the air. This can contribute to smog, respiratory issues, and it also can affect your gas mileage. Also, if you live in a jurisdiction with mandatory exhaust testing then your vehicle would likely fail and result in fines and/or mandatory repairs. Finding a solution now could save a major headache in the future.
Sometimes, the simplest solution is the right one! If you’re getting a P0171 code reading then start with the easiest troubleshooting tips and move on if the issue is not resolved. Once the repair is done, your car and the environment will thank you.
Vince G here with ScannerAnswers. Mike and Matt made me fill out this bio… I write on this site once-in-a-while when I’m not fishing or biking. I love fast cars and on weekends I sometimes work on them. I help with this site because I believe everyone should own and be able to use a wireless bluetooth OBD2 scan tool.