1994 Lexus LS 400FACTORY OEM SERVICE PROCEDURE

ECM Power Source Circuit (Ignition Keyed)

  1. Ensure ECM ground circuits are okay. See ECM GROUND CIRCUITS . For access to ECM, remove glove box. Leave electrical connectors attached to ECM. Turn ignition on. Measure voltage between chassis ground and terminal No. 22 (Black/Red wire) of ECM connector E12. To identify ECM connectors and terminals, see Figure.
  2. If battery voltage is present, ECM keyed (ignition) power circuit is okay. If battery voltage is not present, measure voltage between chassis ground and terminal No. 9 (Black/Orange wire) of ECM connector E12. If battery voltage is present, go to step 5).
  3. If battery voltage is not present, check IGN fuse (10-amp). See COMPONENT LOCATIONS  under INTRODUCTION. If fuse is blown, repair circuit. If fuse is okay, check ignition switch. See STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT section.
  4. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
  5. Measure voltage between chassis ground and terminal No. 13 (Black/Orange wire) of ECM connector E12. If battery voltage is not present, replace ECM. If battery voltage is present, check EFI fuse (20-amp). See COMPONENT LOCATIONS  under INTRODUCTION.
  6. If EFI fuse is blown, repair circuit. If EFI fuse is okay, check EFI main relay. See RELAYS  under MODULES, MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 13 (Black/Orange wire) of ECM connector E12. If circuit is okay, repair circuit between battery and EFI fuse.
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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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