LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2003 >> IS 300 Base, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 39 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0120: Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair (Using Lexus Scan Tool)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair (Using Lexus Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
  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). Opening percentage should be 64-96 percent and voltage should be 4.6-5.1 volts with a fully open throttle. Release accelerator pedal. Opening percentage should be 8-20 percent and voltage should be 2.0-2.9 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.
  2. Access ECM at left front of engine compartment. Turn ignition on. Backprobing connector, measure voltage between ECM E2 connector terminals No. 23 (Blue/Red wire) and No. 22 (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.
  3. Turn ignition on. Backprobing connector, measure voltage between terminals No. 22 (Brown wire) and No. 25 (Yellow/Green wire) at ECM E2 connector. Voltage should be .4-1.0 volt with throttle fully closed and 3.2-4.8 volts with throttle fully open. Backprobing connector, measure voltage between terminals No. 22 (Brown wire) and No. 24 (Black wire) at ECM E2 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. Disconnect TP sensor 4-pin connector. Measure resistance between TP sensor 4-pin connector terminal Blue/Red and Brown wires. If resistance is 1.25-2.35 k/ohms, go to next step. If resistance is not 1.25-2.35 k/ohms, replace TP sensor.
  5. Disconnect 5-pin MAF meter connector and ECM E2 connector. Read throttle opening angle on hand-held tester. If throttle opening percentage with accelerator pedal released is zero percent, and with accelerator pedal depressed is 64-96 percent, replace ECM. If throttle opening percentages are not to specification, repair wiring or replace connector as necessary.
NOTE: If throttle position is 100 percent when releasing throttle pedal, ETA (Brown wire) circuit is open. If throttle position is zero percent when depressing accelerator pedal, VC (Blue/Red wire) or VTA (Yellow/Green wire) circuit is open. If throttle position is not zero percent when releasing accelerator pedal or throttle position is not 100 percent when depressing throttle pedal, VTA2 (Black wire) circuit is open or shorted.
scientia non olet · About LEMON Manuals