my X5 just has 42k miles. I had the SES light on today, so I went to AutoZone to read and clear that. Then I have a code P0171 and P0174
I guess I have a bad O2 sensor(that early at 42k miles??) or I did fill some bad gas (just fill 93octane at Hess)

It states at the printout that
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OEM Number P0171

Definition
Fuel trim bank one condition

Explanation
The powertrain control module uses the oxygen sensor to calculate the air/fuel ratio of the engine.
The computer has recognized a rich or lean condition on one engine bank only.

Probable Causes
1-If bank one and two codes set together suspect fuel pressure or MAF sensor
2-Oxygen sensor defective
3-Ignition misfire-repair
4-Fuel injector problem

Troubleshooting P0171
The PCM has determined that during testing, the fuel system for bank 1 was too lean. (Bank 1 identifies the location of cylinder #1. While bank 2 identifies the cylinders on the opposite bank)

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Oem Number P0174

Definition
Fuel trim bank two condition

Explanation
The ECM has detected a rich or lean air/fuel ration condition on engine bank two

Probable Causes
1-If bank on and two are set together suspect a fuel condition or MAF sensor fault
2-Failed H02s21
3-Ignition misfire condition
4-Fuel ingector problem
5-Engine mechanical condition

Troubleshooting P0174
The PCM has determined that during testing, the fuel system for bank 2 was too lean. (bank 1 identifies the location of cylinder #1, While bank 2 indentifies the cylinders on the opposite bank)
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