02 STS, trouble code P0171 and P0174, also P0385 and P0386
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 02 STS, trouble code P0171 and P0174, also P0385 and P0386 in Past Cadillac Vehicle Discussion; Hey guys new here and I have a problem im going to explain everything so I don't miss any details ...
  1. #1
    DetroitBoi_02STS is offline Cadillac Owners Member
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    02 STS, trouble code P0171 and P0174, also P0385 and P0386

    Hey guys new here and I have a problem im going to explain everything so I don't miss any details that could be linked to my problem. I bought my 02 Seville on March 8th this year the engine light was on when I bought it was the P0385 when I had it checked at autozone, car ran great, periodically my engine light will go off and come back on a day or so later. Now one day I was driving and the car started having a sluggish take off and a slight rough idle got the service light checked and the codes came up that you see in the title and even after my prob my engine light is still going off and coming back on a day or so later . Now the car runs slightly rough its not that bad but it is noticeable, takeoff is a little sluggish but not majorly affecting it, it will get up if I hit the gas but still slightly sluggish. Also when I first had the prob inside the car had a real strong gas / exhaust smell, it smelt like a firecracker went off. I tried the CDC brake cleaner thing on the plenum and nothing happened one last thing about a week before my problem started I noticed my oil was really low just a drop on the dipstick but my mechanic told me just replace a couple quarts and I should be okay don't know if that would have anything to do with this but figure I would mention it sorry I had the write so much I didn't want to miss anything that may be important but this is where I'm at at this moment any advice or anything guys?

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 02 STS, trouble code p0171 and p0174, also p0385 and p0386

    For your 2002 Northstar engine ........

    P 0171 and P 0174 are lean fuel mixture codes, Bank 1 and Bank 2. ANY air leak in the intake air ducting at or after the MAF will set those, as well as the "plenum" between the throttlebody and intake manifold. If anyone has been into the air filter or throttlebody I would initially suspect the intake duct resonator - that black kidney-shaped thing on top of the intake flex duct.

    P 0385 and P 0386 are CranKshaft Position sensor codes - those units that send electrical pulses used for ignition and injector timing reference. There was a batch of faulty units in the 2000 - 2003 series. Symptoms include poor driveability as well as slowdown, slow turn, and slow speed warmup stalls.

    Both these faults are DIY repairable - either search through the pages of Seville, Deville, Cadillac Tech Tips for "How-To's" or Google something like "cadillac forums 2002 Northstar crankshaft position sensor" and "cadillac forums 2002 northstar lean mixture codes" or something close.

    Pictures and diagrams of all the parts in my albums - ^^^ Community tab, Albums, the red Seville - 2 albums, 6 pages.

    BTW, Your car has its own built-in code scanner/reader. Study the correct year/car parts of the sticky post just above this "How to pull codes"> Practice.

  4. #3
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386



    For future reference, always include the code definitions along with the codes. These are so common that some of us have them memorized, but that's the exception to the rule. In the mean time, follow Sub's advice and change the plenum duct and the CKP sensors.

  5. #4
    DetroitBoi_02STS is offline Cadillac Owners Member
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    Sorry im just replying back been busy working everyday. Sorry ill put the description with the code for now on. Also thanks for telling me about the built in code reader, tried it and it helps a lot. I have a update about my situation I was going to try what you guys suggested today when I got paid but when I tried to start my car to pick up my check it wont idle, I have to keep my foot on the gas and now im getting trouble code (P0106 Manifold Absolute Pressure (MAP) System Performance) which is showing up as current and p0174 is back current but p0171 is still listed as history tho and (P0410 Secondary Air Injection (AIR) System) popped up 2 days ago and is now listed as history. So before I do anything, with these new events do you or anybody suggest that I should focus on the MAP being the culprit all along or still what was suggested to me can trigger those codes or is this is a whole nother prob all together. This really frustrating me, thanks in advance guys

  6. #5
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    Vacuum leaks - MAP - lean mixture code(s) ............... MAP = Manifold Absolute Pressure - most probable because of a vacuum leak during intake power vacuum monitoring. Based on a LOT of sensor inputs the MAP readings can fall in or out of spec depending on a LOT of operating conditions, including power demand, atmospheric pressure, intake air temperature, intake airflow, engine torque delivery, blah, blah, blah.

    Diagnose and repair the lean fuel mixture and the CKP codes and you might find that the MAP code(s) go to History.

  7. #6
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    I'd still start with the CKP sensors and the plenum duct.

  8. #7
    DetroitBoi_02STS is offline Cadillac Owners Member
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    Ok guys, im just waiting on my friend to bring my parts (he has the hook up at o reillys hee hee) and when its get done ill let yall know if the ckp worked but my idle problem is gone I was running 87 in there when gas was 4.84 for premium my neighborhood mechanic said it needs premium I didn't know what would happen if I ran 87 in it. But after I replaced it with premium it idled again so unless it was a just a coincidence replacing the gas seems to fix my idleing problem.

  9. #8
    basscatt's Avatar
    basscatt is offline Cadillac Owners Master
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    Quote Originally Posted by DetroitBoi_02STS View Post
    Ok guys, im just waiting on my friend to bring my parts (he has the hook up at o reillys hee hee) and when its get done ill let yall know if the ckp worked but my idle problem is gone I was running 87 in there when gas was 4.84 for premium my neighborhood mechanic said it needs premium I didn't know what would happen if I ran 87 in it. But after I replaced it with premium it idled again so unless it was a just a coincidence replacing the gas seems to fix my idleing problem.
    ----------------------------
    Ok guys, im just waiting on my friend to bring my parts

    here is what you need - and what you SHOULD pay -
    for the crankshaft sensors - and be sure to replace BOTH -
    and DO NOT let anyone install any aftermarket sensors -

    ACDelco 213-1578 - $37.97 - with free shipping -
    from amazon.com -
    and -
    ACDelco 213-1579 - $43.70 - with free shipping -
    also from amazon.com

    my idle problem is gone
    I was running 87 in there when gas was 4.84 for premium
    my neighborhood mechanic said it needs premium


    your 02 Seville was built and designed to run on 87 octane gas -
    you neighborhood "mechanic" is ignorant -
    meaning he knows nothing about Cadillacs -

    even if your car required premium gas -
    running regular wouldn't cause a vacuum leak -
    and running premium wouldn't "fix" it -

    if you didn't find the leak -
    or replace either the plenum boot - or PCV elbows -
    you still have a big vacuum leak -

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    Quote Originally Posted by DetroitBoi_02STS View Post
    but my idle problem is gone I was running 87 in there when gas was 4.84 for premium my neighborhood mechanic said it needs premium I didn't know what would happen if I ran 87 in it. But after I replaced it with premium it idled again so unless it was a just a coincidence replacing the gas seems to fix my idleing problem.
    Your shadetree mechanic is very wrong - and you have my permission to tell him I said so. When all else fails, read your owner's manual - the gasoline recommendations for your 2002 STS are in there. (It's 87 octane except for trailer towing, mountain climbing, and racing)

    (Know that I run almost exclusively 87 octane Shell - and the car will do 143 with it with no problems. No idle problems. No engine problems. and no gas mileage changes)

  11. #10
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    How could anyone who calls himself a "mechanic" claim that octane rating will have any affect on the idle. You need a new "mechanic".
    basscatt likes this.

  12. #11
    amunderdog is offline Cadillac Owners Connoisseur
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    Re: 02 STS, trouble code P0171 and P0174, also P0385 and P0386

    Quote Originally Posted by Ranger View Post
    How could anyone who calls himself a "mechanic" claim that octane rating will have any affect on the idle. You need a new "mechanic".
    "he has the hook up at o reillys"
    Was my first clue.

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