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P0172

135K views 40 replies 17 participants last post by  sheila 
#1 ·
I did a search on this code, and found the service bulletin regarding dirty injectors. I also googled it and came up with a couple hits regarding dirty MAF or stuck canister purge valve.

The deal is, I've got an 06 3.5 that was having evap leak codes as well as this one. I replaced the canister vent solenoid, and the evap leak codes are gone, but the p0172 still comes back. Checked MAF, looks spotless and shiny inside. Took off the purge valve and was not able to blow through it, so I assume that means its not stuck open. So does it just need an injector cleaning?

The vehicle has expired tags, there was a problem with the title transfer so we didn't get a notice beforehand, now the vehicle is due for emissions and its giving me this crap. For that reason running a fuel treatment through the tank isn't really an option, so is there anything I can do to avoid paying the dealer to clean the injectors?
 
#3 ·
^It can also point to a leaking intake manifold.

As for avoiding the dealership, they are the only ones that can do a pressure fuel injector cleaning. Be wary of a shop doing it, as alot of shops just dump gumout or similiar product in the tank and tell you they "cleaned them"

MOST of the fuel injector cleaner sold over the counter is snake oil, not worth the landfill it creates.
 
#4 ·
I put a can of berrymans b12 in it and told them to run the car over the weekend, we'll see if it helps. It was what the parts counter guys recommended, they usually give me good info. I really hope it works, I hate having to explain every time a car needs money spent on it...
 
#5 ·
Didn't clear it, freeze frame data shows long term fuel trim at -21.09% Anybody have any clues?
 
#7 ·
Well, it seems to say that its either leaking injectors or a bad O2 sensor. My boss told me to just send it over to the dealer, so I did.
 
#8 ·
Ah geez, didn't realize I hadn't updated this thread. The dealer came back with a diagnosis of a bad fuel pump, apparently they believe it was basically overpumping. So, I replaced it with a carter. Same code returned.

I just got hold of them again, and they said to send it back over and they will recheck it for free. The tech over there also said that there was fuel in the oil, now I was unable to smell any on the dipstick or in the fill hole, so I don't know where he got that conclusion, but I have to change it before I send it back.
 
#9 ·
Can you test the fuel pressure yourself? If so does it maintain the pressure when the engine is off for 10 or more minutes?

Also, with the engine off, pull the vacuum line off of the fuel pressure regulator and see if any fuel falls from the vacuum line if so replace the regulator.
 
#10 ·
Its back at the dealer at the moment, they are taking a free look at it now. Unfortunately, the 8th gens don't seem to have a FPR, there is a fuel pressure sensor on the pump, but thats it.
 
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#11 ·
Got the car back, apparently the PCM was reading 47% alcohol in the fuel, so I guess it was in E85 mode. They reprogrammed it, I'm having patrol run it over the weekend to complete a driving cycle to be sure it's fixed, then I hope to finally get it through DEQ
 
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#13 ·
Makes siphoning way more fun though
 
#14 ·
That was it, though I had another evaporate leak code. Replaced the canister purge solenoid valve and that fixed it. Now trying to get the emissions monitors ready for testing.
 
#15 ·
The fix

Guys this was very helpful. I know the last post was from back in 2011, but I want to add this for the next person that finds this post like I did by simply googling the problem. I am the head mec at my shop and I see lots of odd things, some take longer to diag and fix than others but I usually fix them. I have this state owned Chevy Impala LS with the exact same problem. P0172 fuel system rich bank 1. My boss has never just allowed me to throw parts at at a vehicle until its fixed, he wants to know why the part is bad and how can I prove it. that being said after spending hrs looking for the problem, I found this forum and this post.
THE FIX.......
Went on my Snap-on Verdict went to Engine, Functional Test, Output Controls, Fuel Trim (reset)
The Problem.......
State vehicle, using surplus state fuel (all NC state cars are flex fuel) too much E85 in the mix. Next fill up less E85/more fuel. The vehicle could not make the proper fuel adjustments for the new mix.
Police car fixed, passed all monitors, passed NC state inspection, and is now back on the road with no check eng light on and pulling people over........all good except the last part
 
#18 ·
I have a 2008 Impala 3.5L Flex and was curious if the fuel trim reset would be the best option? I have code P0172 and the MAF sensor is clean along with a newly replaced O2 sensor. When looking at the freeze frame on the code reader the specs for the MAP and MAF sensors are just a little out of the designated operating range. The vehicle has not ran on E-85, and there are no vacuum leaks. If a reset it the best option is there any idea on a ballpark price range if I take it to a shop?
 
#21 · (Edited)
I know that this is an old thread, but I just had this code come up. Discovered my air filter intake housing is cracked at the bottom and is slightly ajar. I definitely have to fix that thing, but could that cause this code by ruining my MAP sensor?

I was getting the P0449 as well and replaced the vent solenoid a few months ago. Now I'm getting this p0172 coming up.

I don't have a Flex, BTW. Just a regular 08 LT Gas 3.5 guzzler :)
 
#23 ·
Hey Fellas, We have a about 25-30 of these 3.9 liter Impala Police cars, in our fleet.
Some of them getting up in the years and mileage. Had one today with the P0172 code. Using our MDI box and laptop, loaded with the GM TechII and the GM website, was able to find a flash for this. New calibration number was 12641985, which this particular car did not have.
So, even after flashing the new info, check engine light came back on, when I road tested it. Proceeded to reset both the fuel trim and the fuel composition, cleared all DTC's and drove it around the block.
No check engine light and fuel trim numbers seem to be in order. (+10 to -10)
Worth noting, that another tech threw some O2 sensors at this, back in Feb and of course, it did not fix the problem.
Thanks for the good info. Trying to flash more and more cars to properly fix these issues, but not always this easy.

JT
City Of Winter Park Fl Fleet Maint.
 
#24 ·
Hey Fellas, We have a about 25-30 of these 3.9 liter Impala Police cars, in our fleet.
Some of them getting up in the years and mileage. Had one today with the P0172 code. Using our MDI box and laptop, loaded with the GM TechII and the GM website, was able to find a flash for this. New calibration number was 12641985, which this particular car did not have.
So, even after flashing the new info, check engine light came back on, when I road tested it. Proceeded to reset both the fuel trim and the fuel composition, cleared all DTC's and drove it around the block.
No check engine light and fuel trim numbers seem to be in order. (+10 to -10)
Worth noting, that another tech threw some O2 sensors at this, back in Feb and of course, it did not fix the problem.
Thanks for the good info. Trying to flash more and more cars to properly fix these issues, but not always this easy.

JT
City Of Winter Park Fl Fleet Maint.
Did you reset fuel composition, alcohol % ?
 
#26 ·
I'm actually dealing with this nonsense right now with my 2008 Impala, 3.5 flex. It was reading 39% alcohol. Never once put e85 in it. Always used 87 octane. Kept getting the P0172 code. I went to fill up the other day and accidentally filled it with 93 octane. After driving until the tank was empty, the light came back on at about 1/4 tank. Checked the levels again and it had actually dropped to 34% alcohol. Cleared the code, filled it again with 93 and drove until it was empty. Filled it today, checked it again and it was reading at 24% alcohol. I'm thinking I may have gotten some bad gas. But it seems that putting in high test and driving it until it's almost empty seems to be a big help. I'm going to take another reading after this tank has dropped down to 1/4 and see if the alcohol number still drops.

I'm not sure if anyone else has tried doing this, but it definitely seems to be cleaning out whatever was in there.
 
#27 ·
I also am having a reoccurring P0172 code (2009, 3.9L). I have a Craftsman branded Innova scanner. I don't see a way to reset the alcohol percentage. Are my options to either find a GM scanner or go to the dealer? I put an O2 sensor in it, which didn't help. I haven't cleaned the MAF or checked the plugs yet (about 98000 mi). Is there a convenient place to connect a vacuum gauge on these engines?
 
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