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roger a holthaus Posted on Apr 08, 2015
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Po 122 problem light on had changed sensor problem not fixed trans not shifting right horrible jurks when it shifts.

Turn engine off then restart it may run ok for awhile

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Bruce Augustine

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  • Subaru Master 471 Answers
  • Posted on Apr 15, 2017
Bruce Augustine
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P0122 - OBD-II Trouble Code
Our automotive experts have put together the following information about the P0122 diagnostic trouble code. We've provided the common symptoms that occur when this code is set along with the frequent repairs that address the issues related to the P0122 code.
OBD II Fault Code

  • OBD II P0122
Fault Code Definition
  • Throttle/Pedal Position Sensor/Switch "A" Circuit Low Input
What Does Mean?
The Throttle Position Sensor/Switch is located on the Throttle Body of the Intake Manifold and the Pedal Position Sensor/Switch is part of the Accelerator Pedal assembly. These sensors provide precise input from the driver's foot in terms of how MUCH power is needed from the engine and, how URGENTLY power is needed. As the Throttle Position Sensor is rotated from its base resting position to full acceleration, typically, it sends an increasing voltage signal to the Powertrain Control Module (PCM). This increasing or decreasing voltage signal is used by the PCM to manage the Air Fuel Ratio and Spark Timing of the engine as well as other Emissions System Components.
Code P0122 triggers when the Throttle/Pedal Sensor/Switch "A" Circuit has low output
Symptoms
  • Check Engine Light will illuminate
  • In many cases, no abnormal symptoms may be noticed
  • In some cases, the engine may be hard starting
  • In some cases, the engine may hesitate during acceleration
Common Problems That Trigger the P0122 Code
  • Defective Throttle Position Sensor or Switch
  • Torn or jammed floor mats
  • Faulty or corroded Throttle/Pedal Position Sensor/Switch wiring or connections
Common Misdiagnoses
  • Throttle or Pedal Position Sensor is replaced when the real problem is a poor connection or chafed wiring
  • Pedal Position Sensor is replaced when the real problem is torn or damaged floor mats
Polluting Gases Expelled
  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
P0122 Diagnostic Theory for Shops and Technicians
When diagnosing a P0122 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive while paying close attention to engine load, Mass Air Flow grams per second, RPM, and road speed on a data streaming scan tool. As you drive the vehicle, compare these values to the Throttle/Pedal Position Sensor PID or parameter ID. The Throttle/Pedal Position Sensor voltage values should rise and fall with changes in engine RPM and engine load.
Check the Throttle/Pedal Position Sensor connector with the key on-engine off. There needs to be a steady 5 volt reference voltage and an excellent ground. Find and use the proper engine performance wiring diagram to discern the proper color and position of these wires in the connector.
It is vital to do a key on-engine off test of the Throttle/Pedal Position Sensor by testing the Throttle Position/Pedal Position output from its signal wire. Typically, I operate the Throttle or Pedal manually and watch the rise and fall of its voltage or HTz on a lab scope to see if there are any sensor 'flat spots' or glitches. I test it again and watch the output on a data streaming scan tool to validate the sensor and Electronic Throttle Module(if equipped) connectivity with the PCM.

David Harrelson

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  • Subaru Master 5,456 Answers
  • Posted on Apr 08, 2015
David Harrelson
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P0122 is TPS signal low, which could mean you have a bad TPS, or a fault in the wiring or connector. I suspect a bad Throttle Position Sensor.

Testimonial: "have changed TPS 4 times over last 12 mos.seems to help for a while subaru mechanic said alternator not putting out enough amps i changed it and battery which didnt help.I will check wiring. Thanks anyway"

  • David Harrelson
    David Harrelson Apr 08, 2015

    Check carefully wiring as the + wire supplies both the TPS and MAF I believe, so any fault in this wiring could easily cause your problem as well as burn up TPS.

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I think its the transmission.

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When installed on the assy line

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