DTC C1203/53: ECM Communication Circuit Malfunction: Wiring Diagram
WARNING: This page is about a different car, the 2002 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
For wiring diagram of ECM communication circuit, see Fig 1.
For complete ABS System Wiring Diagrams, see ANTI-LOCK BRAKES in SYSTEM WIRING DIAGRAMS article.