1996 Lexus ES 300FACTORY OEM SERVICE PROCEDURE

ECM Power Source Circuit (Ignition Keyed)

CAUTION: If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction.
  1. Access ECM behind glove box. Turn ignition on. Leave ECM connectors attached. Backprobing connector, connect voltmeter negative lead to terminal No. 16 (Brown wire) at ECM E9 connector (this terminal is grounded). See Figure.
  2. Connect voltmeter positive lead to terminal No. 23 (Black/Orange wire) at ECM E10 connector. If battery voltage is present, ECM power circuit is okay. If battery voltage is not present, go to next step.
  3. Check for an open circuit in wiring harness between ground and terminal No. 16 at ECM E9 connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, go to next step.
  4. Check EFI main relay. See RELAYS  under MODULES, MOTORS, RELAYS & SOLENOIDS. Replace relay as necessary. If relay is okay, go to next step.
  5. If EFI main relay is okay, check EFI fuse. If EFI fuse is blown, check for short to ground in wiring. If EFI fuse is okay, check for open circuit between battery and EFI main relay, and between EFI main relay and ECM.
  6. If circuits are okay, check IGN fuse. If IGN fuse is blown, check for short to ground in wiring. If IGN fuse is okay, check ignition switch. See STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT section. If ignition switch is okay, repair open circuit between ignition switch and EFI main relay, or between EFI main relay and ground.
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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.