PRE-COLLISION: PRE-COLLISION SYSTEM: C1A4B; Stop Light Relay Circuit; 2018 - 2020 MY Sienna [11/2017

Last Modified: 04-05-2023	6.11:8.1.0	Doc ID: RM1000000018YBL
Model Year Start: 2018	Model: Sienna	Prod Date Range: [11/2017 - ]
Title: PRE-COLLISION: PRE-COLLISION SYSTEM: C1A4B; Stop Light Relay Circuit; 2018 - 2020 MY Sienna [11/2017 - ]

DTC

C1A4B

Stop Light Relay Circuit

DESCRIPTION

The skid control ECU (brake actuator assembly) sends a stop light operation request signal to the stop light relay (stop light switch assembly). 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

Both of the following conditions are met:

All of the following conditions are met:
- 3 seconds have elapsed since the ignition switch was turned to ON.
- 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 actuator assembly) is normal.
- The driving support ECU assembly receives a stop light relay circuit malfunction signal from the skid control ECU (brake actuator assembly)

HINT:

The skid control ECU (brake actuator 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 actuator assembly)
Stop LP relay
Rear combination light assembly LH
Rear combination light assembly RH
Center stop light assembly
Harness or connector

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses and bulbs*1 for circuits related to this system before performing the following procedure.
Perform the communication function inspections in Diagnosis System to confirm that there are no CAN communication malfunctions before performing the following procedure.
Click here
- *1: for Bulb Type Stop Light

PROCEDURE

1.	INSPECT TERMINAL VOLTAGE (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) CONNECTOR)

(a) Turn the ignition switch off.

(b) Disconnect the skid control ECU (brake actuator assembly) connector.

*a	Front view of wire harness connector (to Skid Control ECU (Brake Actuator Assembly))

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-5 (STP2) - Body ground	Brake pedal depressed	8 to 14 V
A75-5 (STP2) - Body ground	Brake pedal released	Below 1.5 V
A75-26 (STPO) - Body ground	Ignition switch ON	11 to 14 V
A75-35 (STP) - Body ground	Brake pedal depressed	8 to 14 V
A75-35 (STP) - Body ground	Brake pedal released	Below 1.5 V

(d) Connect the A75 skid control ECU (brake actuator assembly) connector.

Result	Proceed to
The voltage is as specified for every terminal.	A
Only the voltage at terminal STPO is not as specified.	B
Only the voltage at terminal STP is not as specified.	C
Only the voltage at terminal STP2 is not as specified.	D
The voltage at both terminal STPO and terminal STP are not as specified.	E

2.	PERFORM ACTIVE TEST USING TECHSTREAM (STOP LIGHT RELAY)

(a) Turn the ignition switch off.

(b) According to the display on the Techstream, perform the Active Test Stop Light Relay.

Click here

ABS/VSC/TRAC

Tester Display	Test Part	Control Range	Diagnostic Note
Stop Light Relay	Stop light relay (Stop light switch assembly)	ON/OFF	Test possible at vehicle speed of 0 km/h (0 mph)

OK:

The stop lights turn on and off correctly in response to the operation of the Active Test.

GO TO STEP 4

3.	CHECK FOR DTCS (PRE-COLLISION SYSTEM)

(a) Clear the DTCs.

Click here

(b) According to the display on the Techstream, perform the Active Test Stop Light Relay.

Click here

ABS/VSC/TRAC

Tester Display	Test Part	Control Range	Diagnostic Note
Stop Light Relay	Stop light relay (Stop light switch assembly)	ON/OFF	Test possible at vehicle speed of 0 km/h (0 mph)

Click here

OK:

DTC C1A4B is not output.

USE SIMULATION METHOD TO CHECK

REPLACE BRAKE ACTUATOR ASSEMBLY (SKID CONTROL ECU)

4.	INSPECT STOP LP RELAY

(a) Remove the STOP LP relay from No. 3 engine relay block.

(b) Measure the resistance according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
3 - 4	Voltage is not applied between terminals 1 and 2	Below 1 Ω
3 - 4	Voltage is applied between terminals 1 and 2	10 kΩ or higher

*1	STOP LP Relay

REPLACE BRAKE ACTUATOR ASSEMBLY (SKID CONTROL ECU)

REPLACE STOP LP RELAY

5.	CHECK WIRE HARNESS AND CONNECTOR (BRAKE ACTUATOR ASSEMBLY (SKID CONTROL ECU) - STOP LIGHT LP RELAY)

(a) Turn the ignition switch off.

(b) Remove the STOP LP relay from No. 3 engine room relay block.

*a	No. 3 Engine Room Relay Block (Relay Holder)

*a	Front view of wire harness connector (to Brake actuator assembly (skid control ECU))

(d) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
A75-26 (STPO) - Relay holder terminal 1	Always	Below 1 Ω
A75-26 (STPO) or Relay holder terminal 1 - Body ground	Always	10 kΩ or higher

(e) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

(f) Install the STOP LP relay to the No. 3 engine room relay block.

REPAIR OR REPLACE HARNESS OR CONNECTOR

6.	INSPECT STOP LP RELAY (POWER SOURCE CIRCUIT)

(a) Turn the ignition switch off.

(b) Remove the STOP LP relay from the No. 3 engine room relay block.

*a	No. 3 Engine Room Relay Block (Relay Holder)

Standard Voltage:

Tester Connection	Condition	Specified Condition
Relay holder terminal 2 - Body ground	Ignition switch ON	11 to 14 V
Relay holder terminal 5 - Body ground	Always	11 to 14 V

(d) Install the STOP LP relay to the No. 3 engine room relay block.

REPLACE STOP LP RELAY

REPAIR OR REPLACE HARNESS OR CONNECTOR

7.	INSPECT STOP LP RELAY

(a) Remove the STOP LP relay from No. 3 engine relay block.

(b) Measure the resistance according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
3 - 4	Voltage is not applied between terminals 1 and 2	Below 1 Ω
3 - 4	Voltage is applied between terminals 1 and 2	10 kΩ or higher

*1	STOP LP Relay

REPLACE STOP LP RELAY

8.	CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY LH)

(a) for Bulb Type Stop Light

(1) Turn the ignition switch off.

(2) Disconnect the A75 brake actuator assembly (skid control ECU) connector.

(3) Disconnect the K35 rear combination light assembly LH connector.

(4) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-35 (STP) or K35-3 (B) - Body ground	Brake pedal depressed	8 to 14 V

(5) Reconnect the K35 rear combination light assembly LH connector.

(6) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

(b) for LED Type Stop Light

(1) Turn the ignition switch off.

(2) Disconnect the A75 brake actuator assembly (skid control ECU) connector.

(3) Disconnect the K18 rear combination light assembly LH connector.

(4) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-35 (STP) or K18-4 (B) - Body ground	Brake pedal depressed	8 to 14 V

(5) Reconnect the K18 rear combination light assembly LH connector.

(6) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

REPLACE REAR COMBINATION LIGHT ASSEMBLY LH

9.	CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - CENTER STOP LIGHT ASSEMBLY)

(a) Turn the ignition switch off.

(b) Disconnect the A75 skid control ECU (brake actuator assembly) connector.

(d) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-35 (STP) or m1-2 (STP) - Body ground	Brake pedal depressed	8 to 14 V

(e) Connect the m1 center stop light assembly connector.

(f) Connect the A75 skid control ECU (brake actuator assembly) connector.

REPLACE CENTER STOP LIGHT ASSEMBLY

10.	CHECK WIRE HARNESS AND CONNECTOR (SKID CONTROL ECU (BRAKE ACTUATOR ASSEMBLY) - REAR COMBINATION LIGHT ASSEMBLY RH)

(a) for Bulb Type Stop Light

(1) Turn the ignition switch off.

(2) Disconnect the A75 brake actuator assembly (skid control ECU) connector.

(3) Disconnect the L52 rear combination light assembly LH connector.

(4) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-35 (STP) or L52-3 (B) - Body ground	Brake pedal depressed	8 to 14 V

(5) Reconnect the L52 rear combination light assembly LH connector.

(6) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

(b) for LED Type Stop Light

(1) Turn the ignition switch off.

(2) Disconnect the A75 brake actuator assembly (skid control ECU) connector.

(3) Disconnect the L33 rear combination light assembly LH connector.

(4) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
A75-35 (STP) or L33-4 (B) - Body ground	Brake pedal depressed	8 to 14 V

(5) Reconnect the L33 rear combination light assembly LH connector.

(6) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

REPLACE REAR COMBINATION LIGHT ASSEMBLY RH

REPAIR OR REPLACE HARNESS OR CONNECTOR

11.	INSPECT STOP LP RELAY

(a) Remove the STOP LP relay from No. 3 engine relay block.

(b) Measure the resistance according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Condition	Specified Condition
3 - 4	Voltage is not applied between terminals 1 and 2	Below 1 Ω
3 - 4	Voltage is applied between terminals 1 and 2	10 kΩ or higher

*1	STOP LP Relay

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE STOP LP RELAY

12.	CHECK WIRE HARNESS AND CONNECTOR (BRAKE ACTUATOR ASSEMBLY (SKID CONTROL ECU) - STOP LIGHT LP RELAY)

(a) Turn the ignition switch off.

(b) Remove the STOP LP relay from No. 3 engine room relay block.

*a	No. 3 Engine Room Relay Block (Relay Holder)

*a	Front view of wire harness connector (to Brake actuator assembly (skid control ECU))

(d) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
A75-26 (STPO) - Relay holder terminal 1	Always	Below 1 Ω

(e) Reconnect the A75 brake actuator assembly (skid control ECU) connector.

(f) Install the STOP LP relay to the No. 3 engine room relay block.

REPLACE STOP LP RELAY

REPAIR OR REPLACE HARNESS OR CONNECTOR