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System Test

NOTE: For terminal identification referenced, see Fig 1. Connectors are viewed from back.
  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.
  2. Using a DVOM, backprobe connector. Check for battery voltage between ECU harness connector "B" (+) terminal and chassis ground. See Fig 1. 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 Figure or Figure under WIRING DIAGRAM.
    Fig 1: Electronic Power Steering ECU Connector
    G93I84127Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. Using ohmmeter, backprobe connector. Check for continuity between ECU harness connector GND terminal and chassis ground. See Fig 1. 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 Figure or Figure under WIRING DIAGRAM.
  4. Raise and support vehicle. Connect ohmmeter leads between ECU harness connector SPD and GND terminals. See Fig 1. 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 Figure or Figure under WIRING DIAGRAM.
  6. Check for continuity between ECU harness connector GND terminal and SOL (-) terminal, between ECU harness connector GND terminal and SOL (+). See Fig 1. 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 Figure or Figure under WIRING DIAGRAM.
  7. Measure resistance between ECU harness connector SOL (-) terminal and SOL (+) terminal. See Fig 1. 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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