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Home >> Toyota >> 1995 >> Tercel Base, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Tests W/Codes >> Diagnostic Testing >> Code P0120 - Throttle Position Sensor (TPS) Circuit Malfunction >> Diagnosis & Repair
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Diagnosis & Repair

  1. Connect scan tester to DLC3 connector. See Figure. Turn ignition on. Turn on scan tester. Monitor throttle valve opening percentage. Opening percentage should be approximately 10 percent with fully closed throttle.
  2. Depress accelerator pedal to floor (WOT). Opening percentage should be approximately 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 TPS 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 TPS component connector terminals No. 1 and 4. Resistance should be 2.5-5.9 k/ohms. Measure resistance between terminals No. 1 and 3. Resistance should be .2-5.7 k/ohms with throttle fully closed and 2.0-10.2 k/ohms with throttle fully open.
  5. If any resistances measured are NOT within specification, replace TPS. See the REMOVE/INSTALL/OVERHAUL article. If all resistances measured are within specification, connect TPS harness connector.
  6. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between terminals VTA and E2. See Figure. Voltage should be .3-.8 volt with throttle fully closed and 3.2-4.9 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 connector, measure voltage between terminals VCC and E2. See Figure. Voltage should be 4.5-5.5 volts.
  9. If voltage is within specification, inspect VCC circuit for open. If voltage is NOT within specification, replace ECM and retest.
Fig 1: Identifying TPS Harness Connector Terminals
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