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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2002 Lexus GS 300. 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, measure voltage between terminals No. 35 (Blue/Yellow wire) and No. 34 (Brown wire) at ECM E5 connectors. 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.
  2. Turn ignition on. Backprobing, measure voltage between terminals No. 34 (Brown wire) and No. 25 (White/Red wire) at ECM E2 and E5 connectors. Voltage should be .4-1.0 volt with throttle fully closed, and 3.2-4.8 volts with throttle fully open. Backprobing, measure voltage between terminals No. 34 (Brown wire) and No. 24 (Yellow/Red wire) at ECM E2 and E5 connectors. Voltage should be 2.0-2.9 volts with throttle fully closed, and 4.6-5.1 volts with throttle fully open. If voltage is not as specified, go to next step. If voltage is as specified, replace ECM and retest.
  3. Check TP sensor operation. See SYSTEM & COMPONENT TESTING - GS300, IS300, GS430, LS430 & SC430 article. Replace TP sensor as necessary. If TP sensor is okay, check for short or open circuit in wiring harness between ECM E3 connector and TP sensor. See WIRING DIAGRAMS article. Repair wiring as necessary.
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