Got engine codes P0171 and P0174 - General info - 2003 Silverado 5.3L, 150K miles, only modification is a K N cold air intake. Apologize in advance for the length ...

General info - 2003 Silverado 5.3L, 150K miles, only modification is a K&N cold air intake.

Apologize in advance for the length of this

About a week ago when the weather got colder (for south Louisiana that is), my truck started running rough. Few days later the check engine light came on. Took it to AutoZone and got engine codes P0171 and P0174. Here is what the printout they gave me said.

Troubleshooting 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 Cause:
1. If bank one and two codes set together, suspect fuel pressure or MAF (Mass Air Flow) sensor
2. Oxygen sensor defective
3. Ignition misfire-repair
4. Fuel injector problem

Troubleshooting P0174
Definition: Fuel trim bank two condition
Explanation: The ECM has detected a rich or lean Air/Fuel ratio condition on engine bank two.
Probable cause:
1. If bank one and two are set together, suspect fuel pressure or MAF (Mass Air Flow) sensor
2. Failed HO2S21 (Heated onygen sensor - Bank 2 Sensor 1)
3. Ignition misfire condition
4. Fuel injector problem
5. Mechanical engine problem

Trying to avoid taking my truck to the shop (I'm a broke student and don't know any mechanics I trust here). I have the ability to fix some of the stuff listed but lack the ability to definitively say it's one thing. I don't want to shadetree mechanic it and just start replacing stuff. After reading on the net for awhile, I'm guessing excess oil on the air filter could be affecting the MAF and will try to test it (tapping on it while running, checking voltage output).

Anyone with tips/things to check that would help me out? Thanks in advance.

Ok, I'll bite. Lets start here. What maintenance have you done?

Checking and cleaning the MAF is easy. Read here: How to Inspect and Clean a Mass Air Flow Sensor (MAF)

lzn - I would I have done little maint. Oil changes, try to keep the air filter clean. Been a while since I've done other stuff - fuel filter, spark plugs. Never have changed the O2 sensors, MAF.

EK - thanks for the link. Actually read it yesterday - finding it thru google is what lead me to this site.

I know its been almost a year since your post but im in the same boat as you i believe, My 2004 Silverado had a "MAF" problem too about 8 months ago so i googled the code with my truck and found that autozone sells a MAF cleaner spray to solve the Oil issue coming from the K&N & clogging the MAF. (autozone neglected to tell me about the cleaner, rather said a new MAF would be needed, Good thing i was broke.) But that issue came up as a P0101 i think. My problem now is i have the P0171&0174 codes(fuel trim lean @ upstream O2sensor, left& right bank) any suggestions?
Thanks -Mike, lpxmike@gmail.com

So ,what did the two of you find out?

I to would like to know. I live in Houston Texas and had the same codes come up.
Last weekend replaced the fuel pump and christmas well need less to say my bank is low also.

Thanks Phil
Katy TX

I've got the same codes on my 03 as well would like to know if y'all found out what it was

honestly dude if it happened right when it got cold its probably just your o2 sensors. swap em out and look at the results.