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Home >> Lexus >> 1996 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0120 - Throttle Position (TP) Sensor Circuit Malfunction >> Diagnosis & Repair

Diagnosis & Repair

  1. Remove instrument panel fuse cover. 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 3100-7200 ohms. Measure resistance between terminals No. 1 (Brown wire) and No. 3 (Yellow wire). Resistance should be 340-6300 ohms with throttle fully closed, and 2400-11,200 ohms with throttle fully open. If any reading is not within specification, replace TP sensor. If all readings are within specification, go to next step.
  4. Connect TP sensor harness connector. Access ECM harness connectors behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Turn ignition on. Measure voltage between terminals No. 43 (Yellow wire) and No. 65 (Brown wire) at ECM "B" 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, locate and repair open or short circuit in wiring harness between ECM and TP sensor.
  5. Access ECM harness connectors behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Turn ignition on. Measure voltage between terminals No. 41 (Blue/Red wire) and No. 65 (Brown wire) at ECM "B" 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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