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Home >> Lexus >> 1996 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P1400 - Sub-Throttle Position (Sub-TP) Sensor Malfunction >> Diagnosis & Repair
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Diagnosis & Repair

  1. 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. Remove intake air duct. Disconnect sub-throttle actuator connector. See Fig 1. Measure voltage between ground and terminal No. 42 (Yellow/Blue wire) at ECM "B" connector. See Figure.
  2. Voltage should be .3-.8 volt (throttle closed) and 3.2-4.9 volts (throttle open). Measure voltage between ground and terminal No. 63 (Red/Black wire) at ECM "B" connector. Voltage should be 0-3 volts (throttle closed) and 9-14 volts (throttle open). If voltage is not as specified, go to next step. If voltage is as specified, no problem is detected at this time. Problem is intermittent.
  3. Check SUB-TP sensor. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If sensor is okay, go to next step.
  4. Check for open or short in wiring harness between SUB-TP sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest.
Fig 1: Identifying Throttle Body Connectors (Models With TRAC)
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