LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 1996 >> Tercel Base, Standard >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Control System Tests W/Codes >> Circuit Tests >> DTC P0120 - Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair
April 5, 2026: LEMON Manuals is launched! Read the announcement.

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 TP sensor connector. Turn ignition on. Using DVOM, measure voltage between ground and terminal No. 4 (Light Green Red wire) at TP sensor wiring 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 7).
  4. Check TP sensor. See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article. Replace sensor as necessary. If sensor is okay, go to next step.
  5. Access ECM behind glove box. Turn ignition on. Backprobing ECM connector, measure voltage between terminals No. 16 (Brown wire) and No. 17 (Yellow/Green wire) at ECM E7 connector. See Figure. Voltage should be .3-.8 volt with throttle fully closed and 3.2 -4.9 volts with throttle fully open (WOT).
  6. If voltage is as specified, replace ECM and retest. If voltage is not as specified, check for an open or short in wiring harness between TP sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary.
  7. Access ECM behind glove box. Turn ignition on. Backprobing ECM connector, measure voltage between terminals No. 16 (Brown wire) and No. 18 (Light Green wire) at ECM E7 connector. See Figure. If voltage is 4.5-5.5 volts, check wiring harness for an open i n Light Green/Red wire. If voltage is not 4.5-5.5 volts, replace ECM and retest.
scientia non olet · About LEMON Manuals