Diagnosis & Repair
WARNING: This page is about a different car, the 2003 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
- Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Turn scan tool on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is same as actual intake air temperature, check IAT sensor and ECM connections. Problem is intermittent. If temperature displayed is -40°F (-40°C), go to next step. If temperature displayed is 284°F (140°C) or more, go to step 4.
- Turn ignition off. Disconnect MAF sensor connector. Connect a fused jumper wire between terminals THA and ETHA at MAF sensor harness connector. See Fig 1. Turn ignition on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is 284°F (140°C) or more, replace mass airflow sensor. If temperature displayed is less than 284°F (140°C), go to next step.
- Turn ignition off. Remove fused jumper wire. Backprobing connector, connect a fused jumper wire between terminals THA and ETHA at ECM E4 connector. Turn ignition on. See Figure-Fig 2 . If temperature displayed on scan tool is 284°F (140°C) or more, check for an open in wiring between MAF sensor harness connector and ECM E4 connector. If temperature displayed on scan tool is not 284°F (140°C) or more, replace ECM and retest.
- Turn ignition off. Disconnect MAF sensor connector. See Fig 1. Turn ignition switch ON. Read the intake air temperature value on the OBD-II scan tool or the hand-held tester. If temperature value is -40°F (-40°C), replace mass airflow sensor. If not, go to next step.
- Disconnect ECM E4 connector from ECM. See Fig 3. Turn ignition on. If temperature displayed on scan tool is -40°F (-40°C), repair or replace harness or connector. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest.