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Home >> Toyota >> 2002 >> 4Runner Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0120: Throttle Position Sensor Circuit >> Diagnosis & Repair
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Diagnosis & Repair

  1. If Toyota hand-held tester is available, 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 at driver's side of instrument panel. See Figure. Turn ignition on and then turn hand-held tester on.
  3. Using hand-held tester, monitor throttle valve opening for VTA and VTA2 circuits with accelerator pedal released and with accelerator pedal depressed. VTA circuit is displayed as a percentage and VTA2 circuit is displayed as a voltage. With accelerator pedal released, VTA circuit should be 8-20 percent and VTA2 circuit should be 2.0-2.9 volts. With accelerator pedal depressed, VTA circuit should be 64-96 percent and VTA2 circuit should be 4.7-5.1 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. 11 (Blue/Black wire) and No. 25 (Green/Black wire) at ECM electrical connector E9. See Figure. This is the E2 and VC 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. 11 (Blue/Black wire) and No. 15 (Black/Yellow wire) at ECM electrical connector E9 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. 4 (Green/Yellow wire) at ECM electrical connector E11 and No. 11 (Blue/Black wire) at ECM electrical connector E9 with accelerator pedal released and with accelerator pedal depressed. This is the VTA2 and E2 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 4.7-5.1
  7. Turn ignition off. Check TP sensor. See THROTTLE BODY under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If TP sensor is okay, go to next step. If TP sensor is defective, replace TP sensor with throttle body as an assembly. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 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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