DTC P1789-00: Lost Communication with Gear Shift Control Module "A" from "B" (Sub CPU) Missing Message [10/2022 - ]: 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 HARNESS AND CONNECTOR (SHIFT CONTROL ECU - SHIFT ACTUATOR ECU)
Pre-procedure1
- Disconnect the C35 transmission floor shift assembly (shift control ECU) connector.
- Disconnect the B58 shift control actuator assembly (shift actuator ECU) connector.
- Measure the resistance according to the value(s) in the table below.
Standard Resistance
Tester Connection Condition Specified Condition Result C35-24 (CA4H) - B58-4 (CA4H) Always Below 1 Ω Ω C35-10 (CA4L) - B58-3 (CA4L) Always Below 1 Ω Ω C35-24 (CA4H) or B58-4 (CA4H) - Body ground and other terminals Always 10 kΩ or higher kΩ C35-10 (CA4L) or B58-3 (CA4L) - Body ground and other terminals Always 10 kΩ or higher kΩ Result
Proceed to OK NG
Post-procedure1
- Connect the shift control actuator assembly (shift actuator ECU) connector.
- Connect the transmission floor shift assembly (shift control ECU) connector.
Result:
NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
Result:
OK
See step 2
- INSPECT TRANSMISSION FLOOR SHIFT ASSEMBLY (SHIFT CONTROL ECU)
Pre-procedure1
- Disconnect the B58 shift control actuator assembly (shift actuator ECU) connector.
- Measure the resistance according to the value(s) in the table below.
Standard Resistance
Tester Connection Condition Specified Condition Result B58-4 (CA4H) - B58-3 (CA4L) Ignition switch off 108 to 132 Ω Ω Result
Proceed to OK NG
Post-procedure1
- Connect the shift control actuator assembly (shift actuator ECU) connector.
Result:
OK
REPLACE SHIFT CONTROL ACTUATOR ASSEMBLY (SHIFT ACTUATOR ECU). Refer to REMOVAL [10/2022 - ]
Result:
NG
REPLACE TRANSMISSION FLOOR SHIFT ASSEMBLY (SHIFT CONTROL ECU). Refer to REMOVAL [10/2022 - ]