Brake Booster (Skid Control ECU) Communication Stop Mode [11/2021 - ]: Procedure

WARNING: This page is about a different car, the 2025 Lexus NX 350h, 2024 Lexus NX 350h, 2023 Lexus NX 350h, and 2022 Lexus NX 350h. However, it is still accessible from the selected car via links, so may be relevant.

CHECK FOR OPEN IN CAN BUS LINES (NO. 1 SKID CONTROL ECU (BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY) BRANCH LINE)

Disconnect the cable from the negative (-) auxiliary battery terminal.
Disconnect the A39 No. 1 skid control ECU (brake booster with master cylinder assembly) connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
A39-38 (CA1H) - A39-39 (CA1L)	Cable disconnected from negative (-) auxiliary battery terminal	54 to 69 Ω

Result

Result
OK
NG

Result:

REPAIR OR REPLACE CAN BRANCH LINES OR CONNECTOR (NO. 1 SKID CONTROL ECU (BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY))

Result:

See step 2

CHECK HARNESS AND CONNECTOR (POWER SOURCE CIRCUIT)

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

Standard Resistance

Tester Connection	Condition	Specified Condition
A39-28 (GND1) - Body ground	Cable disconnected from negative (-) auxiliary battery terminal	Below 1 Ω

Reconnect the cable to the negative (-) auxiliary battery terminal.

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

Standard Voltage

Tester Connection	Condition	Specified Condition
A39-14 (+BI1) - Body ground	Ignition switch off	11 to 14 V
A39-31 (IG1) - Body ground	Ignition switch ON	11 to 14 V
A39-42 (IG2) - Body ground	Ignition switch ON	11 to 14 V

Result

Result
OK
NG

Result:

REPLACE NO. 1 SKID CONTROL ECU (BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY). Refer to REMOVAL [11/2021 - ]

Result:

CHECK HARNESS AND CONNECTOR (POWER SOURCE CIRCUIT). Refer to DTC C110E-14: Brake Booster Motor "A" Supply Voltage Circuit Short to Ground or Open [11/2021 - ]