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Home >> Lexus >> 1997 >> LS 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. Turn ignition on. Remove intake air duct. Disconnect sub-throttle actuator connector. See Fig 1. 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. Disconnect SUB-TP sensor connector. See Fig 1. Measure resistance between terminals No. 1 (Brown wire) and No. 3 (Yellow/Green wire) at SUB-TP sensor. Resistance should be 340-6300 ohms (throttle closed) and 2400-11,200 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 resistances are as specified, go to next step. If resistances are 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.
Fig 1: Identifying Throttle Body Connectors (Models With TRAC)
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