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Home >> Toyota >> 2001 >> Prius >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0120: Throttle/Pedal Position Sensor/ Switch Circuit >> Diagnosis & Repair
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Diagnosis & Repair

  1. If using Toyota hand-held tester, go to next step. If Toyota hand-held tester is not available, go to step  4.
  2. Connect hand-held tester to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on and then turn hand-held tester on.
  3. Using hand-held tester, monitor throttle valve opening by reading THROTTLE POS (displayed as a percentage) and THROTTLE POS#2 (displayed as a voltage) with accelerator pedal released and with accelerator pedal depressed. THROTTLE POS is the VTA circuit and THROTTLE POS#2 is the VTA2 circuit. With accelerator pedal released, THROTTLE POS should be 64-96 percent and THROTTLE POS#2 should be 4.6-5.1 volts. With accelerator pedal depressed, THROTTLE POS should be 8-20 percent and THROTTLE POS#2 should be 2.0-2.9 volts. If throttle valve opening readings are not within specification, go to next step. If throttle valve opening readings are within specification, replace ECM. ECM is located behind glove box. See Figure.
  4. Remove glove box for access to ECM with electrical connectors still installed on ECM. See Figure.
  5. Turn ignition on. Using voltmeter, check voltage between terminals No. 2 (Yellow/Red wire) and No. 18 (Brown wire) at ECM electrical connector E8. See Figure. This is the VC and E2 terminals on ECM. Voltage should be 4.5-5.5 volts. If voltage is specification, go to next step. If voltage is not within specification, replace ECM.
  6. Ensure ignition is still on. Using voltmeter, check voltage between terminals No. 18 (Brown wire) and No. 23 (Pink wire) at ECM electrical connector E8 with accelerator pedal released and with accelerator pedal depressed. See Figure. This is the E2 and VTA terminals on ECM. Also, check voltage between terminals No. 18 (Brown wire) and No. 21 (Blue wire) at ECM electrical connector E8 with accelerator pedal released and with accelerator pedal depressed. This is the E2 and VTA2 terminals on ECM. Ensure voltage is within specification. See TP SENSOR VOLTAGE SPECIFICATIONS AT ECM  table. If any voltage reading is not within specification, go to next step. If all voltage readings are within specification, replace ECM.
    TP SENSOR VOLTAGE SPECIFICATIONS AT ECM

    Accelerator Pedal Position & Terminals Volts
    Accelerator Pedal Released
    VTA & E2 .4-1.0
    VTA2 & E2 2.0-2.9
    Accelerator Pedal Depressed
    VTA & E2 3.2-4.8
    VTA2 & E2 4.6-5.1
  7. Turn ignition off. Check TP sensor. See THROTTLE BODY under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If TP sensor is okay, go to next step. If TP sensor is defective, replace TP sensor. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  8. Check for open and short in wiring harness and electrical connectors between TP sensor and ECM. See WIRING DIAGRAMS article. If wiring harness or electrical connector is defective, repair as necessary.
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