Check engine light 1999 Malibu

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ELANG527
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My check engine light came on and the code that came up on the scanner is p0171 system to lean. Can this be an o2 sensor or a bad fuel filter. I just changed the fuel filter a month ago but he same problem happened 2 yrs ago and I changed the fuel filter and that fixed the problem.
Nov 5, 2006 at 7:21 AM
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BUELLXB9RFB
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Causes
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 (K&N, etc.) can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak downstream of the MAF sensor.
Nov 6, 2006 at 1:57 PM
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