DTC C1A4B: Stop Light Relay Circuit [04/2018 - 08/2021]: Description

WARNING: This page is about a different car, the 2021 Toyota Avalon, 2020 Toyota Avalon, and 2019 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.

The skid control ECU (brake booster with master cylinder assembly) sends a stop light operation request signal to the stop light relay (stop light switch assembly). If the skid control ECU (brake booster with master cylinder assembly) detects a malfunction in the stop light relay (stop light switch assembly) circuit, the driving support ECU assembly stores DTC C1A4B.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
C1A4B	Stop Light Relay Circuit	Both of the following conditions are met: All of the following conditions are met: 3 seconds have elapsed since the power switch was turned to on (IG). The battery voltage is 10 V or more for 3 seconds or more. All of the following conditions are met for 1 second or more: Communication between the driving support ECU assembly and skid control ECU (brake booster with master cylinder assembly) is normal. The driving support ECU assembly receives a stop light relay circuit malfunction signal from the skid control ECU (brake booster with master cylinder assembly)	Electronically controlled brake system