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System Test

NOTE: For terminal identification referenced in testing procedure, see Fig 2.
  1. Turn ignition on. Check ECU-IG fuse. If fuse is blown, check for short circuit between fuse box and ECU. If fuse is okay, unplug ECU harness connector.
    Fig 1: Identifying Electronic Power Steering System Components
    G50B15520Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. Using a DVOM, check for battery voltage between terminal "B" (+) terminal and chassis ground. If battery voltage exists, go to next step. If battery voltage does not exist, check for open circuit between ECU-IG fuse and ECU harness connector. See appropriate WIRING DIAGRAMS article:
    • WIRING DIAGRAMS - ES 300
    • WIRING DIAGRAMS - LS 400
    • WIRING DIAGRAMS - SC300 & SC400
      Fig 2: Identifying Electronic Power Steering ECU Connector
      G92F01460Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. Check for continuity between GND terminal and chassis ground. If continuity exists, go to next step. If continuity does not exist, check for open circuit in harness between ECU and chassis ground or poor ground connection. See appropriate WIRING DIAGRAMS article:
    • WIRING DIAGRAMS - ES 300
    • WIRING DIAGRAMS - LS 400
    • WIRING DIAGRAMS - SC300 & SC400
  4. Jack up and support one front wheel. Connect ohmmeter leads between SPD and GND terminals. Spin front wheel while observing ohmmeter. Ohmmeter indication should switch between zero and infinite resistance.
  5. If indications are as specified, go to next step. If indication is not as specified, check for open circuit between speed sensor and ECU SPD terminal. If wiring is okay, replace speed sensor. See WIRING DIAGRAMS.
  6. Check for continuity between GND terminal and SOL (-) terminal, and between GND terminal and SOL (+). If continuity does not exist, go to next step. If continuity exists, check for short between SOL (-) and SOL (+) wires and ground. If wiring is okay, replace solenoid valve. See appropriate WIRING DIAGRAMS article:
    • WIRING DIAGRAMS - ES 300
    • WIRING DIAGRAMS - LS 400
    • WIRING DIAGRAMS - SC300 & SC400
  7. Measure resistance between SOL (-) terminal and SOL (+) terminal. Resistance should be 6-11 ohms. If resistance is as specified, test is complete. Substitute known good ECU and test power steering operation. If resistance is not as specified, check for open circuit or faulty solenoid valve. Repair or replace as required.
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