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Diagnosis & Repair

  1. Connect Toyota hand-held tester or scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Using hand-held tester or scan tool, monitor ECT sensor temperature. If temperature displayed on hand-held tester or scan tool is same as actual coolant temperature, problem is intermittent. Check component and ECM connections. If temperature displayed on hand-held tester or scan tool is -40°F (-40°C), go to next step. If temperature displayed on hand-held tester or scan tool is 284°F (140°C) or more, go to step  4.
  2. Turn ignition off. Disconnect ECT sensor harness connector. ECT sensor is located on transmission side of cylinder head. Connect a jumper wire between ECT sensor harness connector terminals. Turn ignition on. Using hand-held tester or scan tool, monitor ECT sensor temperature. If temperature displayed on hand-held tester or scan tool is less than 284°F (140°C), go to next step. If temperature displayed on hand-held tester or scan tool is 284°F (140°C) or more, replace ECT sensor. Perform proper cooling system bleeding procedure when refilling cooling system. See COOLING SYSTEM BLEEDING under COOLING SYSTEM in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  3. Turn ignition off. Remove jumper wire. Access ECM on driver's side of firewall behind driver's seat, luggage compartment lids and partition board. See Figure. Connect a jumper wire by backprobing between terminals No. 14 (Red/Blue wire) and No. 18 (Brown wire) at ECM harness connector E4. See Figure. Temperature displayed on hand-held tester or scan tool should be 284°F (140°C) or more. If temperature displayed on hand-held tester or scan tool is as specified, repair open in wiring between ECT sensor and ECM. See WIRING DIAGRAMS article. If temperature displayed on hand-held tester or scan tool is not as specified, replace ECM.
  4. Turn ignition off. Disconnect ECT sensor harness connector. ECT sensor is located on transmission side of cylinder head. Turn ignition on. If temperature displayed on hand-held tester or scan tool is not -40°F (-40°C), go to next step. If temperature displayed on hand-held tester or scan tool is -40°F (-40°C), replace ECT sensor.
  5. Turn ignition off. Access ECM on driver's side of firewall behind driver's seat, luggage compartment lids and partition board. See Figure. Disconnect ECM harness connector E4. See Figure. Turn ignition on. If temperature displayed on hand-held tester or scan tool is -40°F (-40°C), repair short in wiring between ECT sensor and ECM. See WIRING DIAGRAMS article. If temperature displayed on hand-held tester or scan tool is not -40°F (-40°C), replace ECM.
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