Fault code P0171
 

The service engine soon light came on the other day and I plugged in my fault code reader and came up with P0171: system too lean (Bank 1).

The car seems to be running fine, although maybe a little lumpy on idle. Does anyone know what the likely culprit is?

Year? engine size? is a good start.

2004, 2.5L. Although this shouldn't make any difference with the fault codes.

I would be looking for a vacuum leak, and checking the intake air boot for splits or cracks. If you don't see anything, get a smoke test to find a vacuum leak.

Turned out to be the MAF. It was cleaned and the code was reset; we'll see how she gets on.

A code p0171 may mean that one or more of the following has happened:

• 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.

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