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Home >> Lexus >> 1998 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P1120: Accelerator Position Sensor Circuit Malfunction >> Diagnosis & Repair (Using Lexus Scan Tool)
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Diagnosis & Repair (Using Lexus Scan Tool)

  1. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn scan tool on. Using Lexus scan tool, monitor accelerator pedal position sensor voltage at VPA and VPA2 circuits. Accelerator pedal position sensor voltage should be .3-.9 volt at VPA circuit and 1.8-2.7 volts at VPA2 circuit with a fully closed throttle.
  2. Depress accelerator pedal to floor (WOT). Accelerator pedal position sensor voltage should be 3.2-4.8 volts at VPA circuit and 4.7-5.1 volts at VPA2 circuit with a fully open throttle. If voltages are within specification, replace ECM and retest. If voltages are not within specification, go to next step.
  3. Access ECM behind glove box. Turn ignition on. Backprobing, measure voltage between ECM E16 connector terminals No. 2 (Blue/Black wire) and No. 18 (Brown wire). See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, replace ECM and retest.
  4. Turn ignition on. Backprobing, measure voltage between ECM E16 connector terminals No. 21 (Yellow/Red wire) and No. 18 (Brown wire). With fully closed throttle, voltage should be .3-.9 volt. With wide open throttle (WOT), voltage should be 3.2-4.8 volts.
  5. Backprobing, measure voltage between ECM E16 connector terminals No. 9 (Red/Blue wire) and No. 18 (Brown wire). With fully closed throttle, voltage should be 1.8-2.7 volts. With wide open throttle (WOT), voltage should be 4.7-5.1 volts. If voltages are not as specified, go to next step. If voltages are as specified, replace ECM and retest.
  6. Check accelerator pedal sensor operation. See SYSTEM/COMPONENT TESTS article. Replace accelerator pedal sensor as necessary. If accelerator pedal sensor is okay, check for short or open circuit in wiring harness and sensor connector between ECM E16 connector and accelerator pedal sensor. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair wiring as necessary.
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