The Dreaded P0171

[ghost.leader07]

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,

 

[Mike534x]

Does your temp gauge read 210, or read a few notches to the left when warmed up?

When you cleaned the throttle body, did you disconnect the battery and let it sit for 30 mins or so, for the system to reset? It seems like there could be a vacuum leak somewhere. Check this thread for more details. On the intake there's a vacuum port near the front, this little plug has a habit of dry rotting and cracking. On my old Envoy, when it went bad it caused the RPMs to sit around 900-1000 RPM until it was replaced, there is also a line at the throttle body for vacuum as well.

What's the maintenance history like? Has it had a tune up, and if so, what plugs/coils were used? There was a post a few years ago, I remember stumbling across that their P0171 was caused by one of the coils, and another was the CAT being bad. There are a good chunk of posts on here for that particular code that involve different fixes for tackling it.

 

[Mooseman]

If you want to read a lot:

p0171 site:gmtnation.com - Google Search

Lots of threads on the subject.

You can check for vacuum leaks using carb cleaner while the engine is idling.

 

[ghost.leader07]

Does your temp gauge read 210, or read a few notches to the left when warmed up?

When you cleaned the throttle body, did you disconnect the battery and let it sit for 30 mins or so, for the system to reset? It seems like there could be a vacuum leak somewhere. Check this thread for more details. On the intake there's a vacuum port near the front, this little plug has a habit of dry rotting and cracking. On my old Envoy, when it went bad it caused the RPMs to sit around 900-1000 RPM until it was replaced, there is also a line at the throttle body for vacuum as well.

What's the maintenance history like? Has it had a tune up, and if so, what plugs/coils were used? There was a post a few years ago, I remember stumbling across that their P0171 was caused by one of the coils, and another was the CAT being bad. There are a good chunk of posts on here for that particular code that involve different fixes for tackling it.

Thanks for responding, my temp seem to be within the normal range 210-225 on a very hot day, is temps related to P0171? I did disconnect the battery before cleaning the throttle body and let it reset but it didn't help since the code was thrown before cleaning the throttle body, about the vacuum port that you mentioned it was a bit loosen but i got it tightened no change regarding the rpm or p0171 code, I've been keeping up with the maintenance no tune up though I've changed the spark plugs and coils with AcDelco ones, I've also replaced my CAT I'm not sure if the welding is completely sealed can it really throw this code? Much appreciation for your help.

 

[NJTB]

Mine got fixed with a new SAIS valve.

 

[Mooseman]

Yep, the SAIS has been known as a source of problems, however, I would recommend deleting this system instead of having to keep fixing this trouble prone system.
Removing Secondary Air Injection System

 

[budwich]

MAP sensors are relatively cheap. You could try replacing it IF you find no vacuum / air leaks in the system. It is likely a 2004 doesn't have a MAF which is the other sensor that could be involved (and is cleanable if there).

 

[ghost.leader07]

Yep, the SAIS has been known as a source of problems, however, I would recommend deleting this system instead of having to keep fixing this trouble prone system.
Removing Secondary Air Injection System

Thanks for responding, I've just done a smoke test for vaccum and I've found a leak near the SAIS area but yet to find the source, could it be the SAIS that's leaking? And concerning the SAIS delete can it be done at home?

 

[Mooseman]

It can be done at home. Just need a plate or find a block off from an 02-03. You just need a tune to delete the related codes. @limequat at lime-swap.com does it for $99 by mail, which is cheaper than the valve itself. You can also get other stuff done at the same time.
Question about having PCM tuned

 

[ghost.leader07]

MAP sensors are relatively cheap. You could try replacing it IF you find no vacuum / air leaks in the system. It is likely a 2004 doesn't have a MAF which is the other sensor that could be involved (and is cleanable if there).

I did get a code for the MAP sensor before replacing the upstream o2 sensor but it disappeared by itself and didn't occur again, I'll check with the leak around the SAIS then maybe I'll replace the MAP to be sure and you're right my TB doesn't have MAF.

 

[budwich]

The "main air measurement vehicle" is the MAP.... so if it is having problems determining what's up, then the resulting "downstream calculations" at going to be fubarred.

 

[ghost.leader07]

[UPDATE]
I've finished my smoke test looking for any leaks I've pumped smoke from both sides (brake booster and the resonator before the large air filter hose) i didn't find any leaks although when testing from the brake booster vaccum line i found that most of the smoke escapes from the air filter box is that normal? I have attached a photo to show the location, Pumping smoke from the resonator side shows no leaks.



I read that the SAIS should work for 30-60 seconds at a cold start to warm up the CAT then it shuts off is that true? I think my SAIS is open even when the engine warmed up.

I'm going to change the MAP as many of you guys suggested it and definitely considering to do a SAI valve delete and tuning the ECM thank s for the suggestion @mosseman

Lastly can a p0171 code cause my RPM to fluctuate between ~650rpm and ~900rpm (~900rpm most of the time) and also the truck stalls a bit when try to accelerate, p0171 is the only persistent code that I have.

Any help is greatly appreciated.

 

[Mooseman]

i found that most of the smoke escapes from the air filter box is that normal?

I wouldn't worry about that too much. It's not a tight seal on the filter side.

I read that the SAIS should work for 30-60 seconds at a cold start to warm up the CAT then it shuts off is that true? I think my SAIS is open even when the engine warmed up.

That is correct. If it's leaking into the exhaust stream after that, it can throw a lean code.

Lastly can a p0171 code cause my RPM to fluctuate between ~650rpm and ~900rpm (~900rpm most of the time) and also the truck stalls a bit when try to accelerate, p0171 is the only persistent code that I have.

Sure could if the PCM is trying to regulate the idle speed and it's getting a misreading of the O2 and/or unmetered air entering the intake.

 

[ghost.leader07]

That is correct. If it's leaking into the exhaust stream after that, it can throw a lean code

is there's a way to test the SAIS for leaking? does unplugging the valve hose help confirming whether it's leaking or not? and when deleting it what should i do with the hose that connects to it?
Cheers!

 

[Mooseman]

There may be a way but I don't know it. All I did was delete the valve and the hoses are still there. The one that goes to the valve I just folded back and hid it. One of these days, I'll remove the whole thing. @xavierny25 has a picture of the whole kit and kaboodle somewhere.

There is this video that shows the testing and correlation between a leaking SAIS and P0171:

Just pull the valve and block it off on the head. Also pull the fuse for this system to prevent the blower from activating. Clear the codes and drive it. You'll get codes for the SAIS but P0171 should be gone.

 

[xavierny25]

You rang???

 

[ghost.leader07]

You rang???
View attachment 95119

You've removed the smog air pump as well??

 

[ghost.leader07]

There may be a way but I don't know it. All I did was delete the valve and the hoses are still there. The one that goes to the valve I just folded back and hid it. One of these days, I'll remove the whole thing. @xavierny25 has a picture of the whole kit and kaboodle somewhere.

Oh i thought i'd have to do something special lol i'll definitely do that

Just pull the valve and block it off on the head. Also pull the fuse for this system to prevent the blower from activating. Clear the codes and drive it. You'll get codes for the SAIS but P0171 should be gone.

Sounds like an easy job and i can definitely eliminate the valve and its headache.. i'm going to try it tomorrow i'd love to see another code rather then seeing the P0171 again lol

Side note:
When starting the engine and erasing the P0171 code while the engine is running my RPM goes back to normal @ ~600rpm but as soon as i push on the pedal it goes back to ~900rpm so i can definitely confirm what you've mentioned about the ECM adjusting due a false O2 reading or unmetered air entering the intake, also when unplugging the hose connected to the SAIS i can hear it working at first then turning off but my RPM jumps to almost 1200rpm before it goes back to ~900rpm i don't know to make of this it wasn't a good test to begin with but i can see some of the impact that SAI valve has on the RPM.

 

[Mooseman]

After that you can take care of getting the PCM tuned. @limequat does have loaners while you send yours in or you can just pick one up at a pick-n-pull for you to use while you send yours to get tuned or just send it in if you can have your truck parked for a week or so while it's out getting tuned.

 

[ghost.leader07]

After that you can take care of getting the PCM tuned. @limequat does have loaners while you send yours in or you can just pick one up at a pick-n-pull for you to use while you send yours to get tuned or just send it in if you can have your truck parked for a week or so while it's out getting tuned.

Let's say that I'm going to delete the SAIS (install a block off plate, remove the relay and fuses) and not doing a tune to PCM right now just the delete will it effect the performance or throw a code (other than the code for the SAIS) i just want to get rid of the valve and fix the lean code for a cheap price just for now and I'll do the tune for ECM later on.. is that possible?

Thanks again @Mosseman

 

[Mooseman]

Yes, it will run fine except for a code or two for SAIS.

 

[ghost.leader07]

Yes, it will run fine except for a code or two for SAIS.

Ok good, just a question about the intake manifold i want to eliminate the fact that it could be leaking so when i did the smoke test on both sides i didn't find any smoke escaping and I've paid extra attention around the intake manifold and there was none I've used a DIY smoke machine and it produced a good amount of smoke after pumping it into the intake i can tell that the whole system is pressurized 'cause i took off a vaccum line after pumping it with enough smoke the smoke came out with a lot of pressure so could that indicate that my intake manifold is sealed no leaking?

One more thing I'd like to add and i find it strange is that when i webt to see if the intake manifold is tighten i found a bit of oil or grease around the intake holes from the outside and i don't have a leak around my valve cover could it be from the intake manifold? I mean i don't think having a small amount of oil around the intake manifold is normal right?

 

[Mooseman]

Could be coming from the valve cover but you can't see it because of the manifold in the way. I wouldn't worry about it too much.

 

[ghost.leader07]

Could be coming from the valve cover but you can't see it because of the manifold in the way. I wouldn't worry about it too much.

Alright good, what about the chances of having a leak from the intake manifold? Is the smoke test that I did good enough to determine the condition of the gasket? I forget to mention that my engine reaches 220-225f at first I thought it could be a problem with my newly installed radiator but i read that it's related to the code I'm getting is that true?

 

[budwich]

I think you need to back up a bit.... the picture that you posted ISN'T the intake manifold... it looks like its the air filter box. There is a lot more to getting at the intake manifold.
Further, testing for air leaks before the throttle body is of no value... only leaks after the throttle body of interest, including those after the engine (ie. exhaust manifold).

oops, I see in later post that you were referring to other tests associated with the intake... sorry.

 

[ghost.leader07]

I think you need to back up a bit.... the picture that you posted ISN'T the intake manifold... it looks like its the air filter box. There is a lot more to getting at the intake manifold.
Further, testing for air leaks before the throttle body is of no value... only leaks after the throttle body of interest, including those after the engine (ie. exhaust manifold).

I know that lol i wasn't talking about the air filter cleaner box i was referring to the intake manifold with MAP sensor attached to it at the top and PCM on the side and as I mentioned i did a smoke test on both sides from the brake booster line and from resonator side and the system was pressurized well i think it was because no smoke was leaking anywhere i even disconnected the fuel pressure regulator vaccum line to see if I'm getting enough smoke into the system so as soon as I pull it out the a lot of pressurized smoke came out.

I can't tell if my intake manifold is sealed and not leaking, any idea how to test it? I don't think i can test it with a smoke machine since the throttle body is closed I'm no mechanic so I could be wrong 😅

 

[Mooseman]

It should be fine, especially if you checked the bolts. Another test would be to have the engine running and spray carb cleaner around the intake to head connections as well as around the injectors. If the engine speed changes, there's a leak.

 

[ghost.leader07]

It should be fine, especially if you checked the bolts. Another test would be to have the engine running and spray carb cleaner around the intake to head connections as well as around the injectors. If the engine speed changes, there's a leak.

I'm going to check the bolts tomorrow, i was going ask about using carb cleaner on the intake how can i access it to spray it's pretty tight in there i wasn't able to spray much unless i have unbolt the PCM base and move it a bit wondering if it's safe to do while testing.

 

[Mooseman]

You can do that if you want. Won't bother anything. Using the straw on the can valve helps get it in there.

 

[ghost.leader07]

You can do that if you want. Won't bother anything. Using the straw on the can valve helps get it in there.

Okay I'll do that and update, thanks.

 

[ghost.leader07]

So i removed the SAIS and I'm wondering what relay and fuse should I pull out? Some people say 54,55,56 I'm not quite sure. Cheers!

 

[Mooseman]

You can pull all of them. All are for Air Injection.

 

[xavierny25]

@ghost.leader07 Borrowed your pic for this(in blue highlighted circle) but don't forget to plug this up. If you dont there will be a whole lot of hot unfiltered air getting into the engine.

 

[BrianF]

After removing my pump and some of the ducting, I just removed one of the underhood fuses. Other than some codes, no driving issues.

The main issue I had was the valve causing an air leak. I just made some plates out of sheet aluminum and sandwiched them between the gasket and valve. That was a couple years ago and everything has been solid since.

 

[ghost.leader07]

To

@ghost.leader07 Borrowed your pic for this(in blue highlighted circle) but don't forget to plug this up. If you dont there will be a whole lot of hot unfiltered air getting into the engine.View attachment 95164

Thanks xavierny25 i've deleted the SAIS and sealed off the tube you've mentioned with a rubber cap but it didn't fix the p0171 code for me i'll have to look elsewhere but at least I've eliminated the SAIS as a source of the problem. i'm going to check for vacuum leak around the manifold intake it's the only place i haven't checked properly.

 

[ghost.leader07]

After removing my pump and some of the ducting, I just removed one of the underhood fuses. Other than some codes, no driving issues.

The main issue I had was the valve causing an air leak. I just made some plates out of sheet aluminum and sandwiched them between the gasket and valve. That was a couple years ago and everything has been solid since.

Yeah i did the same I've removed the relay and mini relay (54/55/56) and fuse from the fuse box and found a block off plate for the SAIS of 03 TB in the junkyard but in my case my air valve was good no leaks but i've removed it anyway since it serves no real purpose.

 

[ghost.leader07]

You can pull all of them. All are for Air Injection.

My SAI valve is gone yet to remove the air pump under the driver side though after plugging the battery back the car ran smooth for a bit i bet my PCM was adjusting while driving cause after a couple of miles my rpm came back to 900rpm with a lean code, i guess i can eliminate the SAI valve as the culprit, i am yet to check for leaks around the intake manifold i'm going to do it tomorrow and to check the bolts as well as you suggested. my best bet is to continue this process of elimination until i get it fixed even though it's quite frustrating lol

 

[budwich]

have you changed out your MAP yet?

 

[ghost.leader07]

have you changed out your MAP yet?

No i haven't replace it yet, could it cause a lean code? I remember having a code P0106 or something like that for the MAP sensor I've also had a code for the o2 sensor i didn't touch the MAP sensor but I've replace the o2 sensor and both codes went away and never got it again, is it possible for the MAP sensor to be faulty and not throw code? Is there any way to test it? Or should i replace it and hope for the best.

 

[ghost.leader07]

[UPDATE] Sorry for making this thread a long one, i'm experimenting with my P0171 lean code and yet to find the source of the issue so what i did so far:

*Checked for vacuum leaks and i didn't find any i've also checked the intake manifold sprayed A LOT of Carb cleaner around the bolts and holes as best as i could since it's quite difficult to get in there but i'm pretty sure i don't have a vaccum leak.
*Deleted my SAIS and still no luck.
*Replaced my O2 upstream sensor and the reading are good fluctuating between 0.1-0.9v and my downstream is doing almost a steady 0.7v.

Now i'm having a suspicion about 2 parts that could be what causing this whole mess i'd appreciate anyone who can help me with that

1st suspect: (MAP sensor) i have had a code for the MAP sensor while having the p0171 i've replaced the O2 sensor and i properly did a code reset and it was gone and never came back but i've been trying to figure out if my MAP sensor is faulty or not so i tried to clean it and it didn't make a different however after unplugging it and putting it back my idle smooths out for a bit before jumping back to ~900RPM it seems like the MAP collecting data before throwing the engine off with a lean code oh by the way whenever i do a code reset while the engine is running at ~900RPM it drops back to the normal range ~600RPM but as soon as i hit the pedal it goes back to ~900RPM i'm wondering what causing this to register this quick? and my car shuts down immediately if the unplug the MAP it's a stupid way of the testing i know.... what i would like to know will the MAP sensor be a faulty one without throwing an engine code?

2nd suspect: (Fuel pressure regulator) this is a weird one, one day i notice a some fuel on the FPR it was coming from the lip beneath the diaphragm i think and there was a smell of gas in the vacuum line on top but without any traces of gas in it just the smell i read that there should no traces of fuel in the vacuum line can anyone confirm this? here's the weird bit the leakage stopped by itself and i can smell a small amount of gas the vacuum but it's barely noticeable but it's there, adding more confusion to this i feel no vacuum or suction coming off the vacuum port on the resonator i mean none i kept it unplugged ran the car for a couple of minutes hoping to see a sign of a bad FPR like gas coming out of the vacuum port but nothing happened and the ran the same @ 900RPM so i kept it unplugged and when on a test drive the car ran the same with the vacuum hose still unattached and no impact on the performance i'm not sure what is the purpose of the vacuum line on the FPR if it's not doing anything? should it be sucking in or pushing out? because it doesn't do either, I've even tried to suck on the damn FPR it felt like i could probably suck some gas into my mouth so i stopped another stupid idea of mine but frustration can make you do silly things LOL anyway i'd really appreciate any help i could get.

Sorry for the long reply....Cheers!