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Home >> Lexus >> 1995 >> ES 300 >> Repair and Diagnosis >> External Pages >> Different car >> Section 12 (Engine Controls - Tests W/Codes - OBD-II) >> Diagnostic Testing >> Code P0120: Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair Procedure
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Diagnosis & Repair Procedure

WARNING: This page is about a different car, the 1995 Lexus LS 400. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect scan tester to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn scan tester on. Monitor throttle valve opening percentage. Opening percentage should be approximately 10 with fully closed throttle. Depress accelerator pedal to floor (WOT). Opening percentage should be approximately 70. If percentages are within specification, inspect all connections. Problem may be intermittent. If percentages are not within specification, go to next step.
  2. Disconnect TP sensor harness connector. Turn ignition on. Using DVOM, measure voltage between ground and Blue/Red wire at TP sensor harness connector. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, go to step 5).
  3. Turn ignition off. Using ohmmeter, measure resistance between terminals No. 1 (Brown wire) and No. 4 (Blue/Red wire) at TP sensor component connector. Resistance should be 4250-8250 ohms. Measure resistance between terminals No. 1 (Brown wire) and No. 3 (Black/Yellow wire). Resistance should be 300-6300 ohms with throttle fully closed and 3500-10,300 ohms with throttle fully open. If any resistances measured are not within specification, replace TP sensor. If all resistances measured are within specification, go to next step.
  4. Connect TP sensor harness connector. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 7 (Yellow wire) and No. 22 (Brown wire) at ECM E13 connector. See Figure. Voltage should be .3-.8 volt with throttle fully closed and 3.2-4.9 volts with throttle fully open (WOT). If voltages are as specified, replace ECM and retest. If voltages are not as specified, check for open or short circuit in Yellow wire or Brown wire between ECM and TP sensor. Repair as necessary.
  5. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals No. 1 (Blue/Red wire) and No. 22 (Brown wire) at ECM E13 connector. If voltage is 4.5-5.5 volts, locate and repair open in Blue/Red wire between TP sensor and ECM. If voltage is not 4.5-5.5 volts, replace ECM and retest.
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