Throttle position sensor
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Cadillac STS Forum - 2005 through 2012 Discussion, Throttle position sensor in Past Cadillac Vehicle Discussion; Hello All, I am new to this forum and will hopefully ask useful questions. I have a 2008 STS v6 ...
  1. #1
    amishmunshi is offline Cadillac Owners Member
    Automobile(s): 2008 STS
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    Throttle position sensor

    Hello All,

    I am new to this forum and will hopefully ask useful questions.

    I have a 2008 STS v6 3.6 RWD. I got a P2138 with Engine Power Reduced error message. I believe I need a new throttle position sensor based on this video - http://www.youtube.com/watch?v=IagzHYB3GHo

    The dealers near my office mentioned that I will have to most likely get the entire gas pedal and the TPS is inbuilt in it. Unfortunately he didn't have one in stock. If I get a generic gas pedal for chevy will it work for the Cadillac STS?

    Thanks,
    Amish.

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  3. #2
    RippyPartsDept's Avatar
    RippyPartsDept is offline Hi, I'm Chris - Please Read My Signature
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    Re: Throttle position sensor

    The throttle body has a sensor built into it and the accel. pedal also has a sensor built into it

    the one on the throttle body is traditionally called the throttle position sensor
    the one on the pedal is usually called a pedal position sensor

    the two sensors are checked against each other by a module (probably the ecm) to make sure that the commanded throttle position (by the pedal sensor) matches the monitored throttle position (by the TPS)

    looking through the service manual quickly i have found that the definition of that code you were given is not really complete

    DTC  P2138 - Accelerator Pedal Position (APP) Sensor 1-2 Correlation
    so that would mean that the two sensors are not matching up (for whatever reason)
    it could be that either the APP or the TPS is faulty and that's why they're not matching up
    and that would require you to change out either the pedal or the throttle body

    but

    I also saw a bulletin that mentions this code intermittently setting off the reduced engine power message due to a problem with the connection between instrument panel harness and the body harness

    Condition
    • Some customers may comment on an intermittent malfunction indicator lamp (MIL) being Illuminated with a message or an indicator that displays Reduced Engine Power.
    • The technician may observe on a scan tool DTC P2138 – Accelerator Pedal Position (APP) Sensor 1-2 Correlation set as Current or in History.
    Cause
    This condition may be caused by water intrusion into the instrument panel (IP) to body harness connector, which carries the APP sensor signals to the ECM/PCM. This water intrusion results in a voltage difference between APP Sensor 1 and APP Sensor 2 that exceeds a predetermined value for more than a calibrated period of time, setting P2138.
    if you have any aftermarket equipment installed (like an alarm or remote start or radio) then all bets are off but if not then this is probably what's going on

    next line of action should probably be to inspect that IP to body harness connector for any corrosion and repair it if you do find any
    Chris Heath (RippyPartsDept) is an ASE Certified GM Parts Consultant at
    Rippy is a Cadillac, Hummer, Saturn & Saab dealership - family owned and operated in Wilmington, NC since 1946
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  4. #3
    amishmunshi is offline Cadillac Owners Member
    Automobile(s): 2008 STS
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    Re: Throttle position sensor

    Hello Chris,

    Thanks for the detailed instructions. I believe I should start using a wrench and check for details instead of just relying on the error codes. I will check it tonight and respond back.

    Amish.

  5. #4
    Cadillac Cust Svc's Avatar
    Cadillac Cust Svc is online now Cadillac Customer Service
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    Re: Throttle position sensor

    Quote Originally Posted by amishmunshi View Post
    Hello All,

    I am new to this forum and will hopefully ask useful questions.

    I have a 2008 STS v6 3.6 RWD. I got a P2138 with Engine Power Reduced error message. I believe I need a new throttle position sensor based on this video - http://www.youtube.com/watch?v=IagzHYB3GHo

    The dealers near my office mentioned that I will have to most likely get the entire gas pedal and the TPS is inbuilt in it. Unfortunately he didn't have one in stock. If I get a generic gas pedal for chevy will it work for the Cadillac STS?

    Thanks,
    Amish.
    Hello Amish,

    Welcome to the forum! It is a great way to interact with other Cadillac customer's and get great advice. I see you are already going to respond back on this thread after you check for details on your vehicle. We are here to offer assistance, so don't hesitate to reach out to us in the future if there is something you think we can help with.

    Regards,

    Laura M.
    Cadillac Customer Service

  6. #5
    EChas3's Avatar
    EChas3 is online now Cadillac Owners Master
    Automobile(s): 2006 STS4 V8 1SG & 2007 STS V8 1SE
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    Re: Throttle position sensor

    Earlier model year STS had some wiring issues related to this circuit. My 2006 got a new pedal before they actually fixed it back in early 2009. I'm not saying this is your issue but Chris may be on to something. Make sure all the wiring/connections is perfect and not stressed at any point.

    If you do need a pedal, don't accept less than the right part.

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