Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Lexus RX 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. 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 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 (Blue/Black 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, ensure MAF connector is okay. If connector is okay, replace MAF sensor and retest system. If temperature displayed is less than 284°F (140°C), go to next step.
- Turn ignition off. Remove fused jumper wire. Access ECM behind glove box. Backprobing connector, connect a fused jumper wire between terminals No. 18 (Brown wire) and No. 22 (Blue/Black wire) at ECM E8 connector. See Figure. If temperature displayed on scan tool is 284°F (140°C) or more, check and repair open in Brown wire or Blue/Black wire between MAF harness connector and ECM E8 connector. If temperature displayed on scan tool is not 284°F (140°C) or more, replace ECM and retest system.
- 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 system. If temperature displayed is not -40°F (-40°C), turn ignition off and go to next step.
- Access ECM behind glove box. Disconnect ECM E8 connector. Turn ignition on. If temperature displayed is -40°F (-40°C), locate and repair short circuit in wiring harness between MAF sensor and ECM. See Figure. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest system.