Circuit Description

WARNING: This page is about a different car, the 2002 Lexus IS 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 ECM. See Fig 1. When the ECM 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 condition is that battery positive voltage is supplied to connector E4 terminal No. 4 (STP). When the brake is on, battery positive voltage is normally applied through the STOP fuse and stop light switch to connector E4 terminal No. 4 (STP) of the ECM, and the ECM turns the cruise control OFF. If the harness connected to connector E4 terminal No. 4 (STP) has an open circuit, connector E4 terminal No. 4 (STP) will have battery positive voltage and the cruise control will be turned OFF.

Trouble Area

Stop Light Switch.
Harness or connector between ECM and stop light switch circuit.
ECM.

Fig 1: Identifying Stop Light Switch Circuit (DTC P1520/52)