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Home >> Lexus >> 1998 >> LS 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P0120: Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair (Using Lexus Scan Tool)

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. Depress accelerator pedal to floor (WOT).
  2. Opening percentage should be 64-96 and voltage should be 4.6-5.1 volts with a fully open throttle. Release accelerator pedal. Opening percentage should be 8-20 and voltage should be 2-2.9 volts with a fully closed throttle. If readings are within specification, replace ECM and retest. If readings are not within specification, go to next step.
  3. Turn ignition on. Backprobing, measure voltage between ECM E13 connector terminals No. 2 (Black/Red wire) and No. 18 (Brown wire). 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.
  4. Turn ignition on. Backprobing, measure voltage between ECM E13 connector terminal No. 18 (Brown wire) and terminals No. 13 (Pink/Blue wire) and No. 20 (Black/Blue wire). With fully closed throttle, VTA circuit (terminal No. 13) voltage should be .4-1 volt and VTA2 circuit (terminal No. 20) voltage should be 2.0-2.9 volts. With fully open throttle, VTA circuit voltage should be 3.2-4.8 volts and VTA2 circuit voltage should be 4.6-5.1 volts. If voltage is not as specified, go to next step. If voltage is as specified, replace ECM and retest.
  5. Check TP sensor operation. See SYSTEM/COMPONENT TESTS article. Replace TP sensor as necessary. If TP sensor is okay, check for short or open circuit in wiring harness and sensor connector between ECM E13 connector and TP sensor. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair as necessary.
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