this is on a 2004 silverado 2500 with a 6 liter engine codes P0171 and P0174 also came up along with P0300
You may have more than one problem. I would start by checking for intake air leaks (which can also cause the P0300 code) or replacing the front (upstream) O2 sensor.
P0171 Chevrolet - Fuel Trim System Lean Bank 1 Read more: https://www.autocodes.com/p0171_chevrolet.html
P0174 Chevrolet - Fuel Trim System Lean Bank 2 Read more: https://www.autocodes.com/p0174_chevrolet.html
P1153 Chevrolet - HO2S Insufficient Switching Bank 2 Sensor 1 Read more: https://www.autocodes.com/p1153_chevrolet.html
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