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Home >> Lexus >> 1998 >> GS 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 OBD-II Scan Tool)

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Turn ignition on. Backprobing, measure voltage between ECM E3 connector terminals No. 2 (Blue/Yellow 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.
  2. Turn ignition on. Backprobing, measure voltage between ECM E3 connector terminals No. 13 (Red/Black wire), No. 20 (Blue/Black wire) and No. 18 (Brown wire - Ground). With fully closed throttle, VTA circuit voltage should be .4-1 volt, and VTA2 circuit 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.
  3. 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 E3 connector and TP sensor. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair as necessary.
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