DTC C1A4B: Stop Light Relay Circuit [09/2015 - 08/2019]: Description

The skid control ECU (brake actuator assembly) sends a stop light operation request signal to the semiconductor power integration ECU (stop light relay). If the skid control ECU (brake actuator assembly) detects a malfunction in the stop light relay circuit, the driving support ECU assembly stores DTC C1A4B.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
C1A4B	Stop Light Relay Circuit	Diagnosis condition: Engine switch on (IG) and battery voltage between 11 and 14 V Malfunction condition: Either of the following conditions is met: When the stop light illumination output (STPO) signal is on, a signal has not been input to the STP 2 terminal for 0.3 seconds or more continuously. When the stop light illumination output (STPO) signal is off, signals input to the STP terminal and STP 2 terminal of the skid control ECU (brake actuator assembly) differ for 0.3 seconds or more continuously.	Lighting system Skid control ECU (Brake actuator assembly) Semiconductor power integration ECU (Stop light relay) Wire harness or connector

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

C1A4B

Stop Light Relay Circuit

Diagnosis condition:

Engine switch on (IG) and battery voltage between 11 and 14 V

Malfunction condition:
Either of the following conditions is met:

When the stop light illumination output (STPO) signal is on, a signal has not been input to the STP 2 terminal for 0.3 seconds or more continuously.
When the stop light illumination output (STPO) signal is off, signals input to the STP terminal and STP 2 terminal of the skid control ECU (brake actuator assembly) differ for 0.3 seconds or more continuously.

Lighting system
Skid control ECU (Brake actuator assembly)
Semiconductor power integration ECU (Stop light relay)
Wire harness or connector