DTC P0571 Stop Light Switch Circuit Malfunction: Description

WARNING: This page is about a different car, the 2007 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.

While driving with cruise control, if the ECM detects that the brake pedal is depressed, the cruise control system will cancel. The stop light switch sends brake pedal status signals to the ECM.

When the brake pedal is not depressed, terminal ST1- is equal to the positive (+) battery voltage and terminal STP is below 1 V. When the brake pedal is depressed, the ECM cancels cruise control operation.

The ECM outputs this DTC when the voltage of terminals ST1- and STP are both below 1 V for 0.5 seconds or more at the same time.

At this time, the set speed is erased, the cruise control operation is canceled, and the power indicator blinks until the main switch is pushed OFF. Cruise control operation is prohibited until the main switch is pushed ON again.

DTC DETECTION CONDITION CHART

DTC No.	DTC Detection Condition	Trouble Area
P0571	ECM detects malfunction of stop light switch circuit under both of following conditions Voltage of terminal STP is less than 1 V for 0.5 seconds or more Voltage of terminal ST1- is less than 1 V for 0.5 seconds or more	Stop light switch Stop light switch circuit ECM