P0171 code showing up WITHOUT a P0174

[tchristian]

I have been getting a recurring P0171 (Bank 1 lean condition) but I have not been getting the P0174 (Bank 2 lean condition) along with it. I assume this rules out a general vacuum leak like MAF/intake boot or DISA valve. But where would the leak possibly occur that only affects cylinders 1-3? Could the lean condition be a clogged injector on those three cylinders? I have also been getting a P0133 (O2 sensor slow response, upstream bank 1). I have recently replaced the O2 sensor when this code first came up (I used an OEM Bosch). Would this be a cause for the other codes or is it a response to the other codes? Thanks for your help.

[Muzz258]

Start by looking at the fuel trims for both banks. Do you have signs of a vacuum leak?

With a hot engine at idle, look in the “Live Data” section of your scanner and record the 4 fuel trims, 2 short term and 2 long term. If any are >8% then you likely have a vacuum leak.
Rev the engine to 3,000 rpm for 30 seconds and watch the short term trims.

• If they reduce significantly, might even go negative, then it is confirmed that you have a vacuum leak to find. Smoke test the engine to find the vacuum leaks. Read: https://www.e46fanatics.com/threads/...#post-18615547
• If they increase (larger positive numbers), then you have a fuel supply issue. Fuel pump or fuel filter.

Check the bank 2 fuel trims and compare them with the bank 1 fuel trims. It could be that you have a bank 2 condition that is close, but not yet, popping the P0174 code.

If only one Total Fuel Trim (bank) is showing a problem, then the problem is limited to that bank only. There are only a few items that are bank specific. They are:

• 
  
  • Coil
  • Plug
  • Injector,
  • Inlet gasket,
  • Cylinder compression,
  • Exhaust gasket
  • Pre-Cat O2 Sensor,
  • Cat,
  • Post-Cat O2 sensor

For example: a loose Pre-cat O2 sensor is an exhaust leak and it will cause lean codes as air gets in between exhaust pulses.

[harrier]

The p0171/0174 distinction is likely a red herring. Unless it is a coil, then it could easily be sensors or fuel pump or leak.

Read this guide:
https://www.e46fanatics.com/threads/...-more.1284608/