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Thread: The curse of the P0121 Code...

  1. #1
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    The curse of the P0121 Code...

    This code is infamous for giving people with larger cams fits...everything from traction control troubles, to shift point issues to just the good ole' P0121 code showing up for seemingly no reason making people scramble to purchase new Throttle Position sensors, adjust their set screws, etc, etc.

    Before I go any further have a gander at the DTC information provided by LS2.com

    http://www.ls2.com/boggs/dtcs/DTC%20P0121.htm

    To outline a few key points

    The MAP is greater than 65 kPa
    The predicted throttle angle does not match the actual throttle angle
    All conditions present for 20 seconds
    Now, that 65kpa map figure comes into play in nearly every LS1 Car/Truck because its the max map setting in most of the calibrations for the sanity test

    Under normal circumbstances a stock cammed A4 will probably idle at around 35-40 map. When switching to a larger cam with more overlap your map readings could go up to as high as 70 or more kpa map which is way outside of the normal boundries. On a stock cammed car you'd probably need to be at around 30% tps to hit that same map number which is where that predicted throttle angle quote comes into play.

    Now onto the last quote the 20 second timeframe. This will Usually come into play more often than not at idle with large cammed vehicles because many times your steady state map will be within the map sanity guidelines so there is a good possibity you might not see this code pop up immediatly.

    There are a few ways you can cure this issue
    a. Do as suggested in the help file which is to just set the min to 0 & max to 100
    b. Adjust them to YOUR liking so you'll be within a reasonable limit. This will help determine if there IS a real issue with your TPS sensor later down the line.

    So there you have it, as good an explanation I can come up with for that bastard code. So the next time you go WOT in your auto LS1 with a large cam & you go from 1st to 4th by 40mph or just a nagging p0121 code for no obvious reason you now have the info needed to fend it off.

    Well, have a good night & Stay Tuned!

    Last edited by Bill@HPTuners; 02-13-2012 at 04:36 PM.
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  2. #2
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    this was my problem

    Thanks for the info.

  3. #3
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    I actually had the 1st to 4th by 40mph issue when I ran into the issue and this info wasn't available way back then so this has been a long time comin'
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  4. #4
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    my car was doing the 1st to 4th by 40 mph also. Also would not let the stall stay locked up. After driving it last night and not seeing the code it actually feels like the shifts are more positive not sloppy like they have been.

  5. #5
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    Hey thanks im sure this is the problem im having. thank you so much.

    Nick
    2008 Denali XL AWD LSA Blower
    2010 CTS-V
    2005 LLY Duramax SAS
    2015 Denali

  6. #6
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    Hey I have this code also. I have a 396, fast intake and a really aggresive fast ramp cam... the car will not rpm past 5900.. acts like it hits a wall.. Ive changed the valve springs and didnt help. Seat pressure around 170.. I jus ordered a slower ramp cam hopen that this may fix it... Do you think this code would be my problem ?? Ive had a local shop tune it so I dont know if he changed this or not..

  7. #7
    Senior Tuner mowton's Avatar
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    I had similar problems with P0101 (X 1.5 airflow values) and P0106 (shifted table down by one level) based on data logging results. I am right on the cusp for the P0121 at 65 Kpa.

    Thanks for the tip
    Last edited by mowton; 07-30-2008 at 08:37 PM.
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    Tuner in Training blown3qtr's Avatar
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    Sorry bastard showed up today in a Home Depot parking lot. I'm sure this is my issue. Thanks Bill!

    '99 silverado 2500 4x4, 408, inlet forward MP122HH, 60# mototrons, borla exhaust, HPT 2bar OLSD

  9. #9
    Potential Tuner erick prouty's Avatar
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    Yes thank you !!!

    My 98 trans am has been running Bad ever sense the CAM !!!
    maybe this will Help me .

  10. #10
    Senior Tuner Frost's Avatar
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    Quote Originally Posted by erick prouty View Post
    Yes thank you !!!

    My 98 trans am has been running Bad ever sense the CAM !!!
    maybe this will Help me .

    This doesn't affect anything other than setting a light (f-body), so it's definitely not the cause of any poor operation...
    Steve Williams
    TunedbyFrost.com


  11. #11
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    Quote Originally Posted by Frost View Post
    This doesn't affect anything other than setting a light (f-body), so it's definitely not the cause of any poor operation...
    Made my 98 Fbody shift into 4th gear at wot by 40mph so it can definitely cause poor operation.
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  12. #12
    Senior Tuner Frost's Avatar
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    Quote Originally Posted by Bill@HPTuners View Post
    Made my 98 Fbody shift into 4th gear at wot by 40mph so it can definitely cause poor operation.
    It will cause WOT (and sometimes part-throttle) shift problems on the 98 only (as far as f-bodies anyway). Otherwise it doesn't affect the way things run as far as the engine calibration is concerned. When I hear "running badly" I don't think of shifting problems, I think more of engine issues, but that may just be me making an assumption
    Steve Williams
    TunedbyFrost.com


  13. #13
    Potential Tuner erick prouty's Avatar
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    It fixed my 98 TRANS AM !!!

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    Quote Originally Posted by Bill@HPTuners View Post
    This code is infamous for giving people with larger cams fits...everything from traction control troubles, to shift point issues to just the good ole' P0121 code showing up for seemingly no reason making people scramble to purchase new Throttle Position sensors, adjust their set screws, etc, etc.

    Before I go any further have a gander at the DTC information provided by LS2.com

    http://www.ls2.com/boggs/dtcs/DTC%20P0121.htm
    To outline a few key points







    Now, that 65kpa map figure comes into play in nearly every LS1 Car/Truck because its the max map setting in most of the calibrations for the sanity test as shown here

    Here is the new posted picture down below

    Uhm, not to bring this back from the dead, but what picture is this?

    Ill go ahead and take the opportunity to fix that image in the link that was dead and post what i believe people are looking for...
    Last edited by Asylumwarp; 02-13-2012 at 09:11 PM.

  15. #15
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    Quote Originally Posted by Asylumwarp View Post
    Uhm, not to bring this back from the dead, but what picture is this?
    Fixed the first post by removing the dead link and reference to it.
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

  16. #16
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    Great post Bill.... just had this happen to mine! Been driving with the new cam for 2 days and it popped on me just a little while ago. Have seen this a couple of times now with the LS2 cammed, lucky I remembered this post of yours... cheers!!
    2000 Trans Am WS6

  17. #17
    I'm a noob at the whole tuning thing and had the P0121 code, among others. After reading this post, I didn't know where to find the settings to adjust in the editor the kpa limits, I kept looking thorough all the General tabs, not thinking to look in the Engine Diagnostics tab. Hope this helps someone.

  18. #18
    TY Brendang2000 Engine Diagnostics tab and if you hover over the p0121 error box it even tells you what to set it as.