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Home >> Toyota >> 2001 >> ECHO 2D Sedan, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P0120: Throttle Position Sensor Circuit >> Diagnosis & Repair
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Diagnosis & Repair

  1. Connect Toyota hand-held tester or scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on and then turn hand-held tester or scan tool on. Using hand-held tester or scan tool, read throttle valve opening percentages with throttle fully closed and fully open. Throttle valve opening percentage should be approximately 10 percent with throttle fully closed and approximately 70 percent with throttle fully open. If throttle valve opening percentages are not within specification, go to next step. If throttle valve opening percentages are within specification, problem is intermittent. Check component and ECM connections.
  2. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Using DVOM, measure voltage between ground and terminal No. 1 (Red/White 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. Check TP sensor. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If problem does not exist, go to next step. If problem exists, replace TP sensor.
  4. Turn ignition off. Connect TP sensor harness connector. Access ECM behind glove box. See Figure. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 9 (Brown wire) and No. 11 (Yellow/Red wire) at ECM harness connector E6. See Figure. Voltage should be .3-1.0 volt with throttle fully closed, and 3.2-4.9 volts with throttle fully open. If voltage is as specified, replace ECM. If voltage is not as specified, repair open or short in wiring between TP sensor and ECM. See WIRING DIAGRAMS article.
  5. Access ECM behind glove box. See Figure. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between terminals No. 1 (Red/White wire) and No. 9 (Brown wire) at ECM harness connector E6. See Figure. Voltage should be 4.5-5.5 volts. If voltage is as specified, repair open in Red/White wire between TP sensor and ECM. If voltage is not as specified, replace ECM.
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