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P0171, P0174. P0300 Issues Resolved

S

Swanson52

Full Member
Joined
Oct 8, 2007
Messages
62
Location
Geneva, NE
I have a 2002 Avalanche 1500 with 90,000 miles.  Mods include KN filter, Hypertech Power Programmer.  Lately the truck has been running VERY rough, throwing the P0171, P0174 and P0300 codes, being way down on power and getting terrible mileage.

After doing extensive research here, I checked the O2 sensors, injectors, and did a fine tooth combing for a vacuum leak, and all of these things checked out fine.

What does that leave?  You guessed it; faulty MAF sensor.  Replaced it today, and its like I bought a new truck.  The throttle response is better than it ever has been, idle is back to nice and smooth, and I suspect my mileage will come back to normal.

Just a fyi for anyone experiencing these problems, as it seems to be fairly common.
 
Do you have to oil the KN filter you have, sometimes you can put too much on and it gets sucked into the MAF
 
I don't have a K&N, but after I bought my '02 in one of the first things I did was buy a can of MAF cleaner and clean the sensor as instructed. The results were outstanding. Better throttle response and fuel mileage got better. Probably about a 10% mileage increase. That's not a whole lot when you only get 10-12 mpg to begin with, but every little bit helps. I have heard about people having problems getting the K& N oil getting in to the MAF and affecting MPG and throttle response. There is a thread that addresses the MAF cleaning issue.
 
Best 5 dollar fix I've run across also. (y)
 
MichiganSilver03 said:
Do you have to oil the KN filter you have, sometimes you can put too much on and it gets sucked into the MAF
Click to expand...

Yes I do, and I tried cleaning the MAF prior to replacing it to no avail.


And I am not sure the issue actually has been resolved; I started the truck this morning to let it warm up (-10 degrees here) and it appears the same issues have surfaced again and the SES light is on.  :E:
 
It looks like you did your home work on this, so if you are sure the 02 sensors are OK and you are running lean on both banks, try testing the fuel pressure on the fuel rail.

You are getting random codes so it will be hard to pin down, the only other idea I can think of is the CATs.
 
:E: :E: :E: :E: I just replaced The MAF this morning and I just replaced the 2 downstream O2's and still the codes that I'm getting are 171 and 174 :E: :E: :E:, I'm replacing those too tomorrow :cool:#7
 
O.K. I fixed it  (y) In my case the reason I was spitting up the codes is because "something " was setting off the Lean condition, which usually means Vacuum related  :cool:. So I start looking and low and behold the plug coming outta the back of my supercharger was slit open :E: so when you accelerated it was fine, keeping the slit closed but when you declerated it would work it's way open and cause a lean condition causing codes 171 & 174 :E: so after replacing ALL the O2 sensors and the MAF sensor,finding out that it was this kinda ticked me off :E:, well the good news is that I have all good"new" parts and now I have too go back and have my H.P tuners updated (it was programmed w/the leak)so my idle is lower than expected, and the 2.80" gear from radix just showed up (better boost) (y) so I'll be throwing that in. Hope this helps. Good luck in your search.. #7
 
My problem is somewhat odd, which is making it hard for me to nail down.  When the ambient outside air temp is anywhere below 20 degrees,  I throw codes and it idles like complete garbage.  The temp warms up past that to, say, 30 degrees (that's the temp when I drove it again yesterday), no codes and no problems.  ??
 
Interesting development; yesterday after it warmed up the truck was running fine.  I filled up with gas and came home.  This morning it was about 2 degrees but the truck warmed up fine with a full tank of gas.  Hmmm...
 
Did ya get the fuel pressure checked yet.
 
Finally had to break down and take her in.  Turns out the intake manifold gaskets are sucked in causing air to leak.  Hence, lean condition.

I am glad I got it tracked down, and glad we bought the extended warranty now!  Truck also has leaky axle seals which are going to be replaced under warranty as well.
 
Ah a vacuum leak. Glad you got her fixed.

I have heard about the intake gaskets being a problem.
 
Maybe bolts were not torqued properly... once??

good luck any ways with fix
 
Swanson52 said:
Finally had to break down and take her in.  Turns out the intake manifold gaskets are sucked in causing air to leak.  Hence, lean condition.

I am glad I got it tracked down, and glad we bought the extended warranty now!  Truck also has leaky axle seals which are going to be replaced under warranty as well.
Click to expand...
(y)Don't you hate vacumm leaks, I know I do. I'm glad you got her fixed (y)#7
 
I have a 2003 Avy 1500.  I was getting the P0171 and P0174 codes, did all the same checks and came up with nothing.  I replaced all 4 O2 sensors and still had a rough idle when cold and a check engine light on.  Finally, I replaced my fuel filter and that seemed to do the trick.

If your MAF sensor was malfunctioning, it could be from too much oil on the K&N air filter.
 
My 2003 was having a rough idle on cold mornings plus the check-engine light was on.  It has 113, 000 miles on it currently.  I had it checked out at the dealership where they said it was throwing these codes, p0171, p0174, p0300.    They diagnosed and found it had bad intake manifold gaskets.  There's rubber parts on these plastic gaskets which can dry out.  Then they leak.  I've only just got it back but the problem appears to be fixed.  I'm $400 lighter in the wallet too. 
 
I too have recently received the check engine w P0171 & P0174 codes.
My '02 has 101K miles and got the same reading last winter with 92K miles.
Replaced the fuel filter at the time and took care of the problem until now.
Getting ready to get it serviced at the local garage.

From what I'm reading on this thread I should look for the following:

1  MAF sensor
2  Faulty O2 sensors
3  Replace air filter w quality unit
4  Cracked manifold gaskets
5  Vacuum leak


Hopefully its one of these items.  If someone has another idea feel free to add to the list.
The good news for the O2 sensors is I live less than 5 miles from NGKs N American plant here in Charleston WV and can have an employee get them at around $10 each.
Since I bought the truck used in Cincy w 69K miles, Im guessing its due for a tuneup anyhow.
 
I've had my check engine light come on a few times over the years on my '04 and of course, it goes away after a few restarts.  I finally bought a code scanner recently and have gotten the P0171.  I ALWAYS happens when I'm accelerating hard like on an on ramp to an interstate.  Before I just start throwing money at new parts, does this info give anybody Amy ideas on where I should start?  Thank you in advance. 
 
Failing intake manifold gaskets are common with these older engines.

I had mine changed in my 2004 many years ago.

If yours has never been changed, you are probably due.

I suggest using Fel-Pro intake gaskets for this repair.
 
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