DTC P1779-49: Gear Shift Control Module Backup Power Supply Internal Electronic Failure [08/2023 - ]: Procedure

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

CHECK VEHICLE CONDITION

Choose the model to be inspected.

Result

Result	Proceed to
w/o Advanced Park (Remote Controlled)	A
w/ Advanced Park (Remote Controlled)	B

Result:

See step 7

Result:

See step 2

CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - SHIFT ACTUATOR ECU)

Pre-procedure1

Disconnect the H116 integration control supply (integrated capacitor) connector.
Disconnect the B56 shift control actuator assembly (shift actuator ECU) connector.

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

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
H116-19 (BUA) - Body ground	Always	Below 1 V	V
H116-9 (BUAE) - Body ground	Always	Below 1 V	V

Result

Proceed to
OK
NG

Post-procedure1

Connect the shift control actuator assembly (shift actuator ECU) connector.
Connect the integration control supply (integrated capacitor) connector.

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

Result:

See step 3

CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - SHIFT CONTROL ECU)

Pre-procedure1

Disconnect the H116 integration control supply (integrated capacitor) connector.
Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.

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

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
H116-1 (BUSE) - Body ground	Always	Below 1 V	V

Result

Proceed to
OK
NG

Post-procedure1

Connect the transmission floor shift assembly (shift control ECU) connector.
Connect the integration control supply (integrated capacitor) connector.

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

Result:

See step 4

CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - POWER DESTRIBUTION BOX ASSEMBLY)

Pre-procedure1

Disconnect the H116 integration control supply (integrated capacitor) connector.
Disconnect the C90 power distribution box assembly connector.

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

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
H116-10 (BUE2) - Body ground	Always	Below 1 V	V

Result

Proceed to
OK
NG

Post-procedure1

Connect the power distribution box assembly connector.
Connect the integration control supply (integrated capacitor) connector.

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

Result:

See step 5

INSPECT POWER DISTRIBUTION BOX ASSEMBLY

Pre-procedure1

Remove the main body ECU (multiplex network body ECU) from the power distribution box assembly.
HINT:

Refer to REMOVAL [08/2023 - ]

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

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Component without harness connected
(Power Distribution Box Assembly)

Standard Resistance

Tester Connection	Condition	Specified Condition	Result
C90-27 or z31-25 (SBAT) - Other terminals	Always	10 kΩ or higher	kΩ

Result

Proceed to
OK
NG

Post-procedure1

Install the main body ECU (multiplex network body ECU) to the power distribution box assembly.
HINT:

Refer to INSTALLATION [10/2022 - ]

Result:

REPLACE POWER DISTRIBUTION BOX ASSEMBLY. Refer to REMOVAL [08/2023 - ]

Result:

See step 6

CHECK HARNESS AND CONNECTOR (INTEGRATED CAPACITOR - DOOR LOCK ASSEMBLY)

Pre-procedure1

Disconnect the H116 integration control supply (integrated capacitor) connector.
Disconnect the D34 front door lock with motor assembly LH connector.
Disconnect the D15 front door lock with motor assembly RH connector.
Disconnect the E16 rear door lock with motor assembly LH connector.
Disconnect the E6 rear door lock with motor assembly RH connector.

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

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
H116-20 (BUA2) - Body ground	Always	Below 1 V	V

Result

Proceed to
OK
NG

Post-procedure1

Connect the rear door lock with motor assembly RH connector.
Connect the rear door lock with motor assembly LH connector.
Connect the front door lock with motor assembly RH connector.
Connect the front door lock with motor assembly LH connector.
Connect the integration control supply (integrated capacitor) connector.

Result:

REPLACE INTEGRATION CONTROL SUPPLY (INTEGRATED CAPACITOR). Refer to REMOVAL [08/2023 - ]

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK DTC OUTPUT (SUB BATTERY SYSTEM)

Pre-procedure1

Turn the ignition switch to ON.

Check for DTCs.

Body Electrical > Sub Battery System > Trouble Codes

Result

Proceed to
NEXT

Post-procedure1

Turn the ignition switch off.

Result:

GO TO SUB BATTERY SYSTEM. Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2023 - ]