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Need Help With P0121 And Trac Off Light

This is a discussion on Need Help With P0121 And Trac Off Light within the Automatic Transmission forums, part of the Drivetrain category; I Am Mew Here. This Is My 4th Trans Am And I Have Only Had This One For 2 Months, ...

  1. #1
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    1998 trans am

    Unhappy Need Help With P0121 And Trac Off Light

    I Am Mew Here. This Is My 4th Trans Am And I Have Only Had This One For 2 Months, It Is A 98 And Has Racing Cam And Stall Converter Added. It Truly Is One Hell Of A Car But I Am Getting A Po121 Tps Code And Trac Off Light Comes On. When This Happens The Trans Shifts Hard And When I Try To Floor It In 2nd Gear It Will Not Even Acknowledge The Throttle. Any Ideas.

  2. #2
    Moderator Cutlass's Avatar
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    1999 Formula WS6 M6-sold
    2001 Silverado Z71

    Well it either needs a new Throttle Position Sensor (TPS), a new PCM, or a wire repair.
    But I did a search and found this GM P.I. (Preliminary information) bulletin.

    #PIP3144B: Poor Acceleration from a Stop or Detonation in Gear at a Stop - keywords code DTC low MIL ping - (Aug 11, 2006)


    Subject: Poor Acceleration from a Stop or Detonation in Gear at a Stop


    Models: 1996-2007 All General Motors Passenger Cars and Light Duty Trucks




    --------------------------------------------------------------------------------

    This PI is being superseded to update model years and instructions. Please discard PIP3144A.


    --------------------------------------------------------------------------------

    The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

    Condition/Concern:
    Customer concern of poor acceleration, detonation or "ping" at idle in drive or reverse, and/or possible DTC P0101, P0106 and/or P0121 set in the PCM. The vehicle will perform properly after attaining a speed of about 30 - 40 mph. The condition may also be described by the customer or the dealer as a hesitation, stall when putting into gear, surge on acceleration (similar to hitting fuel cut or rev limit). The ultimate cause may be a non-holding torque converter stator or damaged stator support shaft within the automatic transmission.

    Note: A torque converter or stator spline concern will not effect engine operation in park or neutral i.e. misfire or rough idle.

    Recommendation/Instructions:
    The following checks should be performed in the event that normal engine driveability checks have not resolved the detonation or "ping" at idle in drive or reverse, lack of power from a stop, stall, surge on acceleration and or hesitation complaint.

    The IAC counts throttle angle and/or MAP voltage and KPA should be compared to a like vehicle in park and in gear after reaching operating temperature. If the counts and map are high or throttle angle is open excessively in comparison this may be a result of high engine load and a torque converter and or stator support shaft related concern.

    If the above information does not lead to a resolve follow torque converter diagnostics listed below.

    The transmission oil cooler outlet line (line to the cooler) should be checked for excessive heat. The Tech II scan tool may be helpful on vehicles equipped with the transmission fluid temperature sensor in the cooler line (mainly front wheel drive). On vehicles that do not have the temperature sensor in the cooler line a temperature probe should be used to check the temperature. The temperature readings should be compared to a like vehicle with the same powertrain option content.

    A stall test (brake torque) may point to a damaged torque converter, the stall RPM speed will be lower then a like vehicle. However, poor engine performance will also produce a lower stall speed RPM.

    If the torque converter stator or stator support is suspect, the transmission should be removed and THE STATOR SUPPORT SHOULD BE INSPECTED FOR SPLINE DAMAGE. If the stator support splines are damaged the transmission should be repaired and new torque converter installed. If damage is not present on the stator support the concern is either internal to the torque converter stator or an engine performance concern.

    Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

  3. #3
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    Yeah I Was Hoping For An Easier Fix That Maybe You Guys Knew Of. I Am A Service Advisor At Chevrolet And I Found That One Also. I Was Just Hoping With All Of The After Market Parts That It Was Something My Techs Did Not Know Of. Good Thing My Trans Tech And I Are Good Friends I Guess. Appreciate The Reply.

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    Member performabuilt's Avatar
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    Change the TPS test parameters to 0 percent min and 100 percent max the cam is causing it

  5. #5
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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

    Quote:
    The MAP is greater than 65 kPa

    Quote:
    The predicted throttle angle does not match the actual throttle angle

    Quote:
    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 as shown here


    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.


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