1994 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

ECM Back-Up Power Circuit (Battery)

  1. Check EFI fuse. See COMPONENT LOCATIONS  under INTRODUCTION. If EFI fuse is blown, repair circuit. If EFI fuse is okay, pull back the right front floor mat. Remove ECM protective cover. Connect Check Harness (09990-01000) between ECM and harness. See USING CHECK HARNESS  under INTRODUCTION.
  2. Measure voltage between chassis ground and terminal No. 33 of ECM connector "A" (Black/Yellow wire). If battery voltage is not present, repair open circuit between ECM and EFI fuse, or between EFI fuse and battery.
  3. If battery voltage is present, check to see if trouble codes remain stored in ECM memory after ignition is turned off. See TESTS W/CODES - EXCEPT OBD-II article in the ENGINE PERFORMANCE section. If trouble codes remain stored, back-up (battery) power circuit is okay. If trouble codes do not remain stored, replace ECM.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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