Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Lexus GS 300. 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. SeeFigure. 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 284°F (140°C) or more, go to step 4. If temperature displayed is -40°F (-40°C), go to next step.
- Turn ignition off. Disconnect MAF sensor connector. Connect a fused jumper wire between terminals No. 4 (White/Red wire) and No. 5 (Brown wire) at MAF sensor harness connector. Turn ignition on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is 284°F (140°C) or more, check MAF sensor connector for corrosion, damage or loose terminals. If connector is okay, replace MAF sensor and retest. If temperature displayed is less than 284°F (140°C), go to next step.
- Turn ignition off. Remove fused jumper wire. Access ECM at left front of engine compartment. Backprobing, connect fused jumper wire between terminals No. 32 (White/Red) wire and No. 34 (Brown wire) at ECM E4 and E5 connectors. See Figure. If temperature displayed on scan tool is 284°F (140°C) or more, check and repair White/Red wire 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. Turn ignition on. If temperature displayed on scan tool is -40°F (-40°C), replace MAF sensor and retest. If temperature displayed is not -40°F (-40°C), turn ignition off and go to next step.
- Access ECM at left front of engine compartment. Leave MAF sensor disconnected. Disconnect E4 and E5 connectors from ECM. Turn ignition on. If temperature displayed is -40°F (-40°C), locate and repair short in White/Red wire or Brown wire between MAF sensor and ECM E4 and E5 connectors. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest.