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Home >> Toyota >> 1995 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Testing >> Code P0120 - Throttle Position Sensor Circuit Malfunction >> Diagnosis & Repair
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Diagnosis & Repair

  1. Connect scan tester to DLC-3. See Figure. Turn ignition on. Turn on scan tester. Monitor throttle valve opening percentage. Opening percentage should be about 10 percent with fully closed throttle.
  2. Depress accelerator pedal to floor (WOT). Opening percentage should be about 70 percent. If percentages are within specification, inspect all connections. Problem may be intermittent.
  3. If percentages are NOT within specification, turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Using DVOM, measure voltage between harness connector terminal No. 4 and ground. See Fig 1. If voltage measured is 4.5-5.5 volts, go to next step. If voltage is NOT 4.5-5.5 volts, go to step  8.
  4. Turn ignition off. Using ohmmeter, measure resistance between TP sensor component connector terminals No. 1 and 4. Resistance should be 4250-8250 ohms. Measure resistance between terminals No. 1 and 3. Resistance should be 300-6300 ohms with throttle fully closed and 3500-10,300 ohms with throttle fully open.
  5. If any resistances measured are NOT within specification, replace TP sensor. See REMOVE/INSTALL/OVERHAUL article. If all resistances measured are within specification, connect TP sensor harness connector.
  6. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector "E7", measure voltage between terminals No. 7 (VTA) and No. 22 (E2). See Figure. Voltage should be .3-.8 volt with throttle fully closed and 2.7-5.2 volts with throttle fully open (WOT).
  7. If voltages measured are within specification, replace ECM and retest. If voltages are NOT within specification, inspect VTA circuit for open or short. See wiring diagram in WIRING DIAGRAMS article. Repair as needed.
  8. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness "E7" connector, measure voltage between terminals No. 1 (VC) and No. 22 (E2). See Figure. Voltage should be 4.5-5.5 volts.
  9. If voltage is within specification, inspect VC circuit for open. If voltage is NOT within specification, replace ECM and retest.
Fig 1: Identifying TP Sensor Harness Connector Terminals
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