Circuit Description

WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.

When the brake pedal is depressed, the stop light switch sends a signal to the ECU. When the ECU receives this signal, it cancels the cruise control. A fail-safe function is provided so that the cancel functions normally, even if there is a malfunction in the stop light signal circuit. The cancel conditions are: battery positive voltage at terminal No. 3 (STP). When the brake is ON, battery positive voltage normally applied through the STOP fuse and stoplight switch to terminal No. 3 (STP) of the ECU, and the ECU turns the cruise control OFF.

If the wiring harness connected to terminal No. 3 (STP) has an open circuit, terminal No. 3 (STP) will have battery positive voltage and the cruise control will be turned OFF. Also, when the brake is ON, the magnetic clutch circuit is cut mechanically by the stop light switch, turning the cruise control OFF. See Figure.