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need help troubleshooting code P0171, P0174

Discussion in 'GM Powertrain' started by N5856Z, Nov 12, 2012.

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  1. N5856Z

    N5856Z New Member

    Hello all,

    I have been getting the check engine light on here lately. been getting code P0174 a few times last week, and today I got P0171 and P0174 which translates to system too lean bank 1 and 2.
    The engine runs a bit rough at idle sometimes, but other than that runs just fine.
    I was wondering if anyone can help me troubleshoot this and get it taken care of before bad things happen.
    I have an 03 Silverado 1500 LS 2WD with 4.8 L

    Thanks
    Jon
     
  2. 99'HEARTBEAT

    99'HEARTBEAT Epic Member Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    Jon, more often than Not, its the 02 Sensor's being problem, and I would also Check for A Vacuum Leak, after that check out the below list of other items, that could Trigger those Codes,

    A Code P0171.....may mean that one or more of the following has happened:


    • The MAF (Mass Air Flow) Sensor is dirty or faulty
      Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF Sensors Leak the silicone potting material used to protect the circuitry.
    • There could be a Vacuum Leak Downstream of the MAF Sensor
    • Possible Cracked Vacuum or PCV line/connection
    • Faulty or Stuck Open PCV Valve
    • Failed or Faulty Oxygen Sensor (bank 1, sensor 1)
    • Sticking/Plugged or Failed Fuel Injector
    • Low Fuel Pressure (possible plugged/dirty fuel filter!)
    • Exhaust Leak between Engine and first Oxygen Sensor
    Possible Solutions:
    A lot of Times, Cleaning the MAF Sensor and Finding/Fixing Vacuum Leaks fixes the Problem. If you're on a Tight Budget, Start there, but that may not be the fix for certain.

    Other Possible Solutions Include:


    • Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF Sensor, and make sure it's dry before reinstalling
    • Inspect all vacuum and PCV hoses, replace/repair as required
    • Inspect all hoses and connections in the air intake system
    • Inspect and/or test the intake manifold gaskets for leakage
    • Check for a dirty fuel filter and proper fuel pressure
    • Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool
    • If you have access, you may want to run a smoke test

    A Code P0174.......may mean that one or more of the following has happened:


    • The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
    • There could be a vacuum leak downstream of the MAF sensor.
    Possible Solutions Include:

    • In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful Not To Damage the MAF Sensor, and make sure it's dry before reinstalling
    • Inspect all vacuum and PCV Hoses, replace if necessary
    • Check for a Dirty Fuel Filter and Proper Fuel Pressure
     
  3. cj03suburban

    cj03suburban New Member

    Hey mike man you in luck. 03 surburban w 170,K+ miles. Mine did the same thing the other day and last month. I replaced my uni gas cap with new one from dlrship. Still happening. Autozone friend onbase hook up scaner to truck and P0171 & P0174 came on. Try out these links I got off of you tube first. All you will pay is for can of MAF cleaner and go from there brother. Good Luck, I will be doing it here once rain has stop.

    http://www.youtube.com/watch?v=_TO7ZC5N-aA

    http://www.youtube.com/watch?v=xQGSkWEC_u4
     
  4. N5856Z

    N5856Z New Member

    hello again,
    I'm still having the same codes P0171 and P0174 coming on, but just the other morning, I started up the truck and it wasnt idling right and then check engine light was flashing. I turned it off and checked the codes, and got the same P0171 and P0174, in addition I got the codes P0101 and P0300. I cleared the codes and they havent come back on yet. but still getting the 171, and 174 codes. my truck is 03 silverado 1500 4.8L with around 165K miles. the truck runs great at all speeds except at the stop lights, just idles between 500 and 1000 rpm.

    I gonna try cleaning the mass airflow sensor and see if that helps.

    anymore suggestions
     
  5. shibby2oo8

    shibby2oo8 Member 2 Years 100 Posts

    The intake is either warped or the intake gaskets are bad. Not a big deal, the plastic intakes on cars now tend to twist/warp after many heat cycles and need to be replaced. You could get lucky with just the gaskets but a dorman intake kit is like $250 and comes with a new intake plus everything you need. See it all the time and what gives it away is rough idleing when cold. The job is pretty straight forward with basic tools, if you unbolt the throttle body and leave it on the engine you wont have to deal with the cooling sytem. One thing to be sure to do is get a 3/8 torque wrench and tighten to proper specs so you dont warp the new one.
     
  6. N5856Z

    N5856Z New Member

    Well here we go again, still getting the P0171 and P0174 codes. Truck runs fine during the summer months but as the weather starts to cool off around here. The codes come back and the truck idles like crap again. Seems to be getting worse this year.

    I had cleaned the mass airflow sensor, but that had no effect.
    Going try checking the oxygen sensors.
    I am being told that there are 4 O2 sensors or this truck. I just bought one and was going to replace it and see if that helps.

    Does anyone know how to check the sensors. The new one I have has 4 wires, not sure what the resistance should be?

    Thanks
    Jon
     
  7. dobey

    dobey Rockstar 3 Years 100 Posts

    Eh? Why would you make that assertion? This problem you assert is the problem, is not at all common. If your engine is putting enough heat into the intake to cause warping, you have some other serious issue than the intake being warped. The composite intakes on GM's engines are quite a heavy duty nylon plastic blend. I have never heard of one warping as you say, or the intake gaskets just going bad. There are plenty of things behind the throttle body, where a vacuum leak can form. Most common on high mileage engines, is the PCV connection. Rubber vacuum lines are going to dry out and deteriorate long before the intake is going to warp, under normal operating conditions.
     
  8. dobey

    dobey Rockstar 3 Years 100 Posts

    There are 4 O2 sensors, yes. There is one prior to each cat, and one after each cat. The ones that may need replacing are the ones prior to the cat. First thing to check on them would be just to pull them and check for excessive carbon build up on them, or if they are whitened or such.

    When were your spark plugs last replaced? They should be replaced every 100K miles or so. Pull and check them if you haven't already. They might not be the problem, but they can help you isolate it.

    Check that there are no holes in the intake tube that are pulling air in, between the MAF sensor and the throttle body. Check the PCV system and check valve. Pull the intake tube, open the throttle body (with the engine off of course), and check for excessive oil deposits in the intake manifold.

    With the miles on your truck, and your description of the behavior, I'd lean heavily toward a vacuum leak due to one or more of the rubber lines failing, and possibly needing to replace the PCV valve itself. A small crack in a rubber hose could easily be sealed up once the rubber heats up, so you would only run into the problem during cold start, during colder times of the year, due to materials shrinkage. This would cause a vacuum leak at cold idle, and could result in the codes your seeing, and the rough idle condition.
     

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