Symptoms of P0171 OBD II Trouble Code
- a lack of power
- detonation (spark knock)
- rough idle
- hesitation/surge on acceleration.
Common Causes of P0171 OBD II Trouble Code
- The MAF (Mass Air Flow) Sensor is dirty or faulty
Note: The use of "oiled"
air filters may cause the MAF to become dirty if the filter is over-oiled.
There is also an issue with some vehicles where the MAF sensors leak the silicone
potting material used to protect the circuitry.
- There could be a vacuum leak downstream of the MAF sensor
- Possible cracked vacuum or PCV line/connection
- Faulty or stuck open PCV valve
- Failed or faulty oxygen sensor (bank 1, sensor 1)
- Sticking/plugged or failed fuel injector
- Low fuel pressure (possible plugged/dirty fuel filter!)
- Exhaust leak between engine and first oxygen sensor