Brake Light Unit Inspection

WARNING: This page is about a different car, the 2016 Mazda CX-5. However, it is still accessible from the selected car via links, so may be relevant.

Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION .)
Remove the following parts:
- Trunk covering (See TRUNK COVERING REMOVAL/INSTALLATION .)
- Trunk board (See TRUNK BOARD REMOVAL/INSTALLATION .)
- Trunk end trim (See TRUNK END TRIM REMOVAL/INSTALLATION .)
- Rear scuff plate (LH) (See REAR SCUFF PLATE REMOVAL/INSTALLATION .)
- Trunk side trim (LH) (See TRUNK SIDE TRIM REMOVAL/INSTALLATION .)
Reconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION .)

Verify that the voltages of each of the terminals are as indicated in the terminal voltage chart.

If the voltage is not as indicated in the chart, inspect the parts under Inspection item (s).

If the system does not work normally even though the parts or related wiring harnesses do not have any malfunction, replace the brake light unit. (See BRAKE LIGHT UNIT REMOVAL/INSTALLATION .)

Fig 1: Identifying Brake Light Unit Connector Terminals

Courtesy of MAZDA MOTORS CORP.

Terminal	Signal	Connection	Test condition	Voltage (V)	Inspection item(s)
A	Ground	Body ground	Under any condition	1.0 or less	Body ground
D	Brake light illumination request signal	Rear body control module (RBCM)	Because this terminal is for communication, integrity determination by terminal voltage is not possible.
F	Power supply	STOP 10 A fuse	Under any condition	B+	STOP 10 A fuse Battery
G	High-mount brake light signal	High-mount brake light	Brake pedal depressed	B+	High-mount brake light
G	High-mount brake light signal	High-mount brake light	Brake pedal not depressed	1.0 or less	High-mount brake light
H	Brake light illumination status signal	DSC HU/CM	B+	Brake pedal depressed	DSC HU/CM
H	Brake light illumination status signal	DSC HU/CM	Brake DSC HU/CM pedal not depressed	1.0 or less	DSC HU/CM
I	Brake switch (No. 1 signal) signal	Brake switch (No. 1 signal)	Brake pedal depressed	B+	Brake switch (No. 1 signal)
I	Brake switch (No. 1 signal) signal	Brake switch (No. 1 signal)	Brake pedal not depressed	1.0 or less	Brake switch (No. 1 signal)
J	Brake light signal	Brake light Rear body control module (RBCM)	Brake pedal depressed	B+	Brake light Rear body control module (RBCM)
J	Brake light signal	Brake light Rear body control module (RBCM)	Brake pedal not depressed	1.0 or less	Brake light Rear body control module (RBCM)