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Home >> Lexus >> 2002 >> IS 300 Base, Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0120: Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair (Using Lexus Scan Tool)
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Diagnosis & Repair (Using Lexus Scan Tool)

  1. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn scan tool on. Using Lexus scan tool, monitor throttle valve opening percentage at VTA circuit and voltage at VTA2 circuit. Opening percentage should be 64-96 percent and voltage should be 4.6-5.1 volts with a fully closed throttle. Depress accelerator pedal to floor (WOT). Opening percentage should be 8-20 percent and voltage should be 2.0-2.9 volts with a fully open throttle. If readings are within specification, replace ECM and retest. If readings are not within specification, go to next step.
  2. Access ECM under protective cover, behind left headlight in engine compartment. Turn ignition on. Backprobing, measure voltage between terminals No. 35 (Blue/Yellow wire) and No. 34 (Brown wire) at ECM E4 connector. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
  3. Turn ignition on. Backprobing, measure voltage between terminals No. 34 (Brown wire) at ECM E4 connector and No. 25 (White/Red wire) at ECM E7 connector. Voltage should be .4-1.0 volt with throttle fully closed and 3.2-4.8 volts with throttle fully open. Backprobing, measure voltage between terminals No. 34 (Brown wire) and No. 24 (Green/Yellow wire) at ECM E4 connector. Voltage should be 2.0-2.9 volts with throttle fully closed and 4.6-5.1 volts with throttle fully open. If voltage is not as specified, go to next step. If voltage is as specified, replace ECM and retest.
  4. Check TP sensor operation. See SYSTEM & COMPONENT TESTING - GS300, IS300, GS430 & LS430 article. Replace TP sensor as necessary. If TP sensor is okay, check for short or open circuit in wiring harness between ECM E4 and E7 connectors and TP sensor. Repair wiring as necessary.
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