1999 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

GS300 & GS400

  1. Access ECM in left front of engine compartment. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 17 (Brown wire) at ECM E3 connector and positive lead to terminal No. 16 (Black/Red wire) at ECM E6 connector. See Fig 1. If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
  2. Check for an open circuit in Brown wire between ground and terminal 17 at ECM E3 connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, go to next step.
  3. Measure voltage between chassis ground and terminal No. 9 (Black/Orange wire) at ECM E6 connector. If 9-14 volts is present, go to step  5. If 9-14 volts is not present, check IGN fuse in junction box behind left kick panel.
  4. If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
  5. Turn ignition on. Measure voltage between chassis ground and terminal No. 10 (Black/Yellow wire) at ECM E6 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI fuse located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. If fuse is okay, go to next step. If EFI fuse is blown, repair cause of blown fuse.
  6. Check EFI main relay located in engine compartment fuse/relay box, at right rear of engine compartment, behind strut tower. See RELAYS  under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 10 at ECM E6 connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If circuit is okay, repair circuit between battery and EFI fuse.
Fig 1: Identifying Electronic Control Module (ECM) Connector Terminals (GS300 & GS400)
G98D11349Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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