Knock Sensor
WARNING: This page is about a different car, the 2003 Lexus SC 430, 2003 Lexus LS 430, 2003 Lexus IS 300, 2003 Lexus GS 430, and 2003 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
Remove knock sensor. See KNOCK SENSOR under SENSORS & SWITCHES in REMOVAL & INSTALLATION - EXCEPT GX470 article. Check for continuity between knock sensor terminal and knock sensor body (hex portion). If continuity does not exist, knock sensor is okay. If continuity exists, replace knock sensor.