1995 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. Connect voltmeter negative lead to terminal No. 16 (Brown wire) of ECM connector E12. Connect voltmeter positive lead to terminal No. 22 (Black/Blue wire) of ECM connector E11. To identify connectors and terminals, see Figure.
  3. 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 E11.
  4. If battery voltage is present, go to step 6). If battery voltage is not present, remove and inspect IGN fuse. If fuse is blown, check for short to ground in wiring. Repair as necessary.
  5. If IGN fuse is okay, check ignition switch. See the STEERING COLUMN SWITCHES article in the ACCESSORIES/SAFETY EQUIPMENT section. If ignition switch is okay, repair open circuit between ignition switch and battery or between ignition switch and ECM.
  6. Turn ignition on. Measure voltage between chassis ground and terminal No. 24 (Black/Orange wire) of ECM connector E11. If battery voltage is not present, replace ECM. If battery voltage is present, check EFI fuse. If EFI fuse is blown, repair circuit.
  7. If 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. 24 of ECM connector E11. 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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