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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
  1. Access ECM at left front of engine compartment. Turn ignition on. Backprobing connector, measure voltage between terminals No. 35 (Blue/Red wire) and No. 34 (Brown wire) at ECM E5 connector. See Figure. Measure voltage between terminals No. 27 (Green/White wire) and No. 26 (Green wire) at ECM E5 connector. If voltage reading is 4.5-5.5 volts at both circuits, go to next step. If voltage is not 4.5-5.5 volts at both circuits, replace ECM and retest.
  2. Backprobing connector, measure voltage between terminals No. 33 (Red/Yellow wire) and No. 26 (Green wire) at ECM E5 connector. See Figure. With fully closed throttle, voltage should be .5-1.1 volt. With Wide Open Throttle (WOT), voltage should be 3.0-4.6 volts. Measure voltage between terminals No. 32 (Black/White wire) and No. 34 (Brown wire) at ECM E5 connector. With fully closed throttle, voltage should be .9-2.3 volts. With WOT, voltage should be 3.4-5.0 volts. If voltage is not as specified, go to next step. If voltage is as specified, replace ECM and retest.
  3. Check accelerator pedal position sensor operation. See Figure. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - GS300, IS300, GS430, LS430 & SC430 article. Replace accelerator pedal position sensor as necessary. If accelerator pedal position sensor is okay, check for short or open circuit in wiring harness between ECM E5 connector and accelerator pedal position sensor. See WIRING DIAGRAMS article. Repair wiring as necessary.
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