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Home >> Lexus >> 1995 >> LS 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - OBD-II >> Diagnostic Testing >> Code P1400: Sub-Throttle Position (Sub-TP) Sensor Malfunction >> Diagnosis & Repair
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Diagnosis & Repair

  1. Access ECM harness connectors behind glove box. Turn ignition on. Backprobing ECM harness connector, measure voltage between ground and terminal No. 12 (Yellow/Green wire) at ECM E13 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. 31 (Red/Black wire) at ECM E14 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. Remove intake air duct. Disconnect SUB-TP sensor connector. Measure resistance between terminals No. 1 (Brown wire) and No. 3 (Yellow/Green wire) at SUB-TP sensor. Resistance should be 200-800 ohms (throttle closed) and 2800-8000 ohms (throttle open).
  4. Measure resistance between terminals No. 1 (Brown wire) and No. 2 (Red/Black wire) at SUB-TP sensor. Resistance should be less than 500 ohms (throttle closed) and infinite (throttle open). If resistance is as specified, go to next step. If resistance is not as specified, adjust SUB-TP sensor. See ADJUSTMENTS article. If adjustment is okay, replace sensor.
  5. 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.
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