lean codes P0171 + P0300

**edsz71** · 03-10-2009, 04:31 PM

Hi All, I'm new here but I have read several posts referring to 02 sensor issues and I think I may have one now. My truck is a 2005 Z71 with a 5.3 that only has 20,000 miles on it. It just developed a terrible missing problem where it feels like half of the engine is dying. It seems to occur at random times i.e. hot/cold, just started/ run for a while, and has on occasion not acted up at all. The only constant is that it is worst at low idle, sometimes dropping to 300r's. When this first occurred the check engine light was flashing. After the problem seemed to correct itself the light stayed solid. Whenever the probem reappears the light will blink while the motor is running poorly. The codes that were stored were P0171 & P0300. If anyone has successfully dealt with this problem and has any ideas ,I could use all the help I can get

**silveradotrailblazer** · 03-10-2009, 06:25 PM

P0171 is fuel trim lean upstream oxygen sensor left cylinder bank. P0300 is engine misfire.I would check fuel preassure and fuel regulator first for leak down, may have a bad injector on that side of engine. I see that your 05 has only 20,000 miles on it. If your trucks sits alot maybe your fuel is bad.

**edsz71** · 03-10-2009, 08:31 PM

It's funny that you would say that. When this all started I had run my fuel tank lower than I have in quite some time. I was wondering if I might have sucked in something from the bottom of the tank. Since I should probably take a look at the fuel filter ,does anyone know where it is located . I haven't begun to look for it yet

**Z71_guy** · 03-10-2009, 09:39 PM

with 20k i would not think that you sucked something up into the filter, i would look at your fuel pressure and the regulator, but it almost sounds like a bad injector, just a guess tho

**jlsparky7** · 03-10-2009, 10:01 PM

I know I say this a lot but wouldnt hurt to try some seafoam or injector cleaner. Cheapest solutions first! Id so seafoam and fuel filter. A fuel filter can be clogged after 1 bad tank of fuel.

**silveradotrailblazer** · 03-11-2009, 04:23 PM

My 05 Z-71 has fuel filter in the tank.

**TRPLXL2** · 03-11-2009, 08:48 PM

Originally Posted by silveradotrailblazer

My 05 Z-71 has fuel filter in the tank.

I can't deny what you are saying because I have never done one on the Silverado, I was just going off of what it says in my service manual. It said that's where it was located for the 05' Silverado with the 5.3, my bad and I apologize for the bad information. I will erase my previous message so I don't confuse anyone........AMY

**edsz71** · 03-18-2009, 05:02 PM

In case anyone is reading this , the problem turned out to be the pre-cat 02 sensor on the drivers side (bank 1). The truck is running perfect now. Another note, When the new sensor was placed and the truck was run up to temperature , the check engine light came on. The post-cat sensor on the same side set the code this time. I cleared the check engine light and am going under the assumption that I probably just cleaned the extra fuel out of the cat itself. The light has stayed off and the truck is now running perfect. Thanks for the support groovy guys and gals!