ECM Back-Up Power Circuit (Battery)
WARNING: This page is about a different car, the 2002 Lexus SC 430, 2002 Lexus LS 430, 2002 Lexus IS 300, 2002 Lexus GS 430, and 2002 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
If circuit or components are faulty, a Diagnostic Trouble Code (DTC) should set. Retrieve DTCs and perform appropriate diagnostic test. See appropriate SELF-DIAGNOSTICS article.