2005 STS 4.6l V8 - P0174 and p0171
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  • 2 Post By MoistCabbage
Cadillac STS Forum - 2005 through 2012 Discussion, 2005 STS 4.6l V8 - P0174 and p0171 in Past Cadillac Vehicle Discussion; I've read a lot of posts about issues that are related to the p0174, p0171, p0068, and p1101 codes but ...
  1. #1
    Brent Messing is offline Cadillac Owners Member
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    2005 STS 4.6l V8 - P0174 and p0171

    I've read a lot of posts about issues that are related to the p0174, p0171, p0068, and p1101 codes but I still can't seem to figure out what is wrong with my STS.

    The issues codes started after I took my car into the dealership to have the right side catalytic converter replaced because I was getting the famous p0420. I also had them flush the transmission as long as it was in the shop. On the way home from the dealership, my car threw the p0174 code. By the time I was able to get it back to the dealer two days later, the car also threw a p0171, p0068 and a p1101. The dealer called me to tell me that they needed to do three things to take care of the issue: replace the vacuum line to the brake booster, tighten the intake manifold bolts and reflash the the ECM per the TSB pertaining to these codes. I gave them a green light for this work and expected to have no more issues.

    On the way home from the dealer, the car again threw the p0174 code. This was obviously a shocker for me because I hadn't even driven the car 3 miles yet. Unfortunitely, I picked up the car right before the dealer closed on Friday afternoon. By Friday evening, the p0171 code came back on too but not the p0068 or p1101.

    I have been fuming over this all weekend trying to figure out what they did to cause these problems. In my frustration, I read every post about these codes I could find and as a result I have replaced the intake manifold gaskets, checked the plenum for cracks and leaks, checked all hoses that are connected to the intake for leaks, sprayed starter fluid around the intake, plenum, throttle body, etc while the engine was running to check for leaks, and checked the the intake for cracks. After doing all of this work today, the p0174 code came back on after about 10 minutes of driving. I have not driving the car enough to know if the other code will come back on too.

    I have a feeling that the dealer will just try to throw expensive parts at the car without putting much thought into it. I would really like to avoid that situation but I am planning on dropping the car off tomorrow morning to let them have another round of fun because the codes only came on right after they worked on the car. Does anyone have any suggestions?

    Thanks,
    Brent

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  3. #2
    valjan1 is offline Cadillac Owners Member
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    they should have changed both converters

  4. #3
    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    It's a vacuum leak, nothing to do with the converters. Have you checked the intake manifold over-pressurization valve? PCV lines and PCV valve grommet?
    dkozloski and dkozloski like this.

  5. #4
    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    Quote Originally Posted by MoistCabbage View Post
    It's a vacuum leak, nothing to do with the converters. Have you checked the intake manifold over-pressurization valve? PCV lines and PCV valve grommet?
    A common place for a leak to be overlooked is where the PCV line connects to the big plastic elbow between the MAF sensor and the throttle body. Sometimes it helps to make a new rubber connector a little longer to provide extra margin as things get moved around.
    Don't mess with Binky Bear!


  6. #5
    Brent Messing is offline Cadillac Owners Member
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    I finally figured out this issue with the help of the dealer. It turns out the the issue was a MAF sensor that was giving false readings. The dealer compared the baseline readings from the MAF with another MAF that they took off a car that was on the lot and the numbers were very different. After they put on a new MAF and reset the code, I have had no more issues. I guess it is pretty hard to fix problems where there isn't a hard failure. I am just glad that my car doesn't have a CEL on anymore. Thanks for your help!

  7. #6
    Charles Warren's Avatar
    Charles Warren is offline Cadillac Owners Fanatic
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    Wtf so maf throws 171 174 I bet that's whats wrong with my raggedy car. I get po2098 171 174

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    1BadCadSTS's Avatar
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    Quote Originally Posted by Charles Warren
    Wtf so maf throws 171 174 I bet that's whats wrong with my raggedy car. I get po2098 171 174
    It very well could. If its providing readings saying less air is entering than actually is then the ECM could throw lean codes under the reasoning that more air must be entering after the MAF.

  9. #8
    Guy.Seminerio is online now Cadillac Owners Connoisseur
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    I love that the dealer actually did this. Take the MAF from the other car and test it out. Excellent.

  10. #9
    Ludacrisvp's Avatar
    Ludacrisvp is offline Cadillac Owners Connoisseur
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    Quote Originally Posted by Guy.Seminerio View Post
    I love that the dealer actually did this. Take the MAF from the other car and test it out. Excellent.
    I'm betting very few would or are able to do this.

  11. #10
    Charles Warren's Avatar
    Charles Warren is offline Cadillac Owners Fanatic
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    guess what...... my damn brake booster hose was off the back of the engine smh. for years ive been wondering why my brakes felt weak. fixed leak and brakes at the same damn time lol. now i have to sefoam or b&g it again

  12. #11
    REALTORBENJAMIN's Avatar
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    I unattached and reattached this guy, reset the check engine light and (touch wood) it hasn't come back on yet. Is this the PCV valve hose that could be throwing the P0174?
    PCVdiagram.jpg

    I also saw this diagram but didn't have time to inspect it on my car
    PCVdiagram2.jpg

  13. #12
    1BadCadSTS's Avatar
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    Re: 2005 STS 4.6l V8 - P0174 and p0171

    Our N* do NOT have a PCV valve.

  14. #13
    REALTORBENJAMIN's Avatar
    REALTORBENJAMIN is offline Cadillac Owners Fanatic
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    Quote Originally Posted by 1BadCadSTS
    Our N* do NOT have a PCV valve.
    I played around with whatever that hose is in the first pic I posted and it took care of the check engine for now... Good timing because my insurance was up and needed to go thru emissions testing... Pass!

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