Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hello Nation,

This is my second discussion on this forum and i need help regarding this code, i have had it for a while and i'm trying to figure out that's triggering it, my truck is a 2004 Trailblazer LT and here's what i did so far:

*I have cleaned the throttle body and replaced the seal.
*Replaced the Upstream O2 Sensor.
*Inspected the hoses and vacuum lines for any apparent tear and i couldn't find any.

I've read that this code related to a vacuum leak though i don't have a smoke machine but i'm building a DIY one hopefully it'll help.

The truck was running fine but i noticed something a bit strange regarding the RPM gauge normally before having the code my RPM is idling at 600-675 range, at start up the RPM rises up to about 1500 RPM (cold start) then it idles at ~600 range but now it sits at ~900 RPM most to the time sometimes it drops to 600 RPM for a bit then goes back to ~900 RPM, i'm thinking is has to do with the P0171 lean condition, could that be the case? I'm also suspecting the SAIS but i'm not quite sure.

Any idea where else should i look or what could the cause?

I'd really appreciate your input,
 

·
Registered
2003 chevy trailblazer_ltz
Joined
·
135 Posts
1. WHAT ENGINE??? If this is a 4.2L six-popper, exhaust manifold cracking is epidemic. The cracks can allow air into the exhaust stream, causing false indications from the O2 sensor.

2. What is your fuel pressure? A weak fuel pump leads to lean fuel mixtures, if the fuel trim can't adjust high enough.

3. Any misfire? A misfire will cause an O2 sensor to read "false lean".
 

·
Registered
Joined
·
9 Posts
This is a start I am not mancanicly inclined but if you look up the code a little more it going to give you several reasons . What it can be I would get it check out to determine what the actual cause is I hope this can help this what I have found on line and there are several reasons it is hard to determine what is actually what is happening
 

·
Registered
2008 chevy trailblazer_lt
Joined
·
9 Posts
My '08 LT threw that code about three weeks ago.

I had a blowout on a freeway and had to sit in the vehicle in 93 degree weather for about 2 hours in air conditioned comfort waiting to get towed.

About an hour into the 2 hour wait the check engine light came on. I checked the code when I got home. Yup, p0171.

Since the truck had never idled for 2 hours before, I presumed that might be the problem. So I used my reader to delete the code. Three weeks and lots of miles later the code has not returned. Of course I haven't idled for two hours again either
 

·
Registered
Joined
·
16 Posts
Schurkey I may have this wrong but if there is a misfire and fuel isn't combusting in a cylinder won't the O2 sensor pick up the extra oxygen that has passed through the cylinder with the unburnt fuel causing a rich condition??
I may not be understanding how this system works if this is wrong.
 

·
Registered
2004 chevy trailblazer_ls
Joined
·
329 Posts
Mines been doing this for years. I spent 2 years chasing it then gave up. It's VERY intermittent, sometimes only twice a year, sometimes every 3 months, lasting about 3 or 4 starts, then back to normal.
A new SAIS valve seemed to fix it for about a year, new exhaust manifold didn't touch it.
What's crazy, it seems to do it after I get off the highway, using cruise control.
 
1 - 8 of 8 Posts
Top