[SOLVED] Code P0171 after changing my spark plugs. - Page 2 - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Air Induction

Air Induction Performance Air Intake/Air Induction Modifications

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Old 01-03-2015, 07:26 PM
Magoojr Magoojr is offline
Junior Member
2006 Chevy TrailBlazer LS EXT
Summit White 4.2L I6 4X4
Join Date: Dec 2014
Location: Yelm, Wa.
Posts: 3
P0171 Code

Originally Posted by jack0723 View Post
Hello all. I just want to share my experience with code P0171 in hopes it helps other out there with the same situation.

This past week, the temp in New York was down between 2F and 5F in the morning, reaching a balmy 15F in the afternoon. That particular day my wife came home from work and told me a yellow light on in the dash came on and the engine was running rough. Sure enough it was the check engine light. I scanned the PCM and found the code P0171 for lean mixture. I did the obvious looking for vacuum leaks, sprayed the intake listening for a RPM change and watching the LTFT, but found nothing. Long story short, I cleaned the MAF and the fuel trims changed for the better - temporarily - so I replaced the MAF. Same problem. Next was the O2 sensor since it seemed slow switching and was not reaching more than 700 mv. I also cleaned the throttle body and plate - still no change. I searched online and found MANY reason and fixes, the one most common being loose intake manifold bolts. Since I already sprayed the intake connections with carb cleaner before, I didn't consider this a problem, but not wanting or liking to just throw (more) parts at it I decided to check the bolts. First, they are not easy to get to, but well worth checking, as most were loose. The last one on cylinder #6, which is the hardest to access was the loosest. I couldn't actually see it, but it was unthreaded at least 1/8". After tightening all the bolts (no I didn't torque them), I started the engine and monitored the LTFT's and they dropped like a rock. I will replace the intake gasket once the weather changes, but for now, the readings are good enough to leave it alone. LTFT readings before the fix were between 12% and 17% at idle, and around 9% when cruising. Readings now are around 7-8% at idle and drifting between 2% to -4% while crusing. I hope this information helps someone out there.

Thanks for the info, I've been dealing with this code for 6 months, cleaned the MAF, air tube, filter box, changed the O2 sensor, had the injectors cleaned and even once it showed cyl 6 being a problem so I switched the coil pack, still same light. I'll check the intake bolts tomorrow. The vehicle has always ran very well, gas mileage is down and this light constantly comes on and off. Thanks again!
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