DTC C1A4B: Stop Light Relay Circuit [05/2019 - 07/2020]: Description

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 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. The auxiliary 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) HINT: The skid control ECU (brake booster with master cylinder assembly) will detect a stop light relay circuit malfunction if any of the following conditions are met: When the voltage at the IG1 terminal is between 11 V and 14 V and the stop light illumination output (STPO) signal is on, a signal has not been input to the STP terminal continuously for 0.3 seconds or more. When the voltage at the IG1 terminal is between 11 V and 14 V and the stop light illumination output (STPO) signal is off, the input signals at the STP terminal and STP2 terminal differ continuously for 0.3 seconds or more.	Skid control ECU (Brake booster with master cylinder assembly) Stop light relay (Stop light switch assembly) Rear combination light assembly LH Rear combination light assembly RH Center stop light set hybrid vehicle control ECU certification ECU (smart key ECU assembly) Harness or connector

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.
- The auxiliary 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)

HINT:
The skid control ECU (brake booster with master cylinder assembly) will detect a stop light relay circuit malfunction if any of the following conditions are met:

When the voltage at the IG1 terminal is between 11 V and 14 V and the stop light illumination output (STPO) signal is on, a signal has not been input to the STP terminal continuously for 0.3 seconds or more.
When the voltage at the IG1 terminal is between 11 V and 14 V and the stop light illumination output (STPO) signal is off, the input signals at the STP terminal and STP2 terminal differ continuously for 0.3 seconds or more.

Skid control ECU (Brake booster with master cylinder assembly)
Stop light relay (Stop light switch assembly)
Rear combination light assembly LH
Rear combination light assembly RH
Center stop light set
hybrid vehicle control ECU
certification ECU (smart key ECU assembly)
Harness or connector