DTC U029A-87: Lost Communication with Hybrid/EV Battery Sensor Module Missing Message [10/2022 - ]: Procedure

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

CHECK DTC OUTPUT (HYBRID CONTROL)

Pre-procedure1

None.

Check and record any HV system DTCs and freeze frame data. Check for DTCs.

Powertrain > Hybrid Control > Trouble Codes

Result

Result	Proceed to
Only U029A-87 is output	A
U029A-87 and other DTCs are output	B

Post-procedure1

Turn the ignition switch off.

Result:

GO TO DTC CHART (HYBRID CONTROL SYSTEM). Refer to DIAGNOSTIC TROUBLE CODE CHART [10/2022 - 10/2024] , or Refer to DIAGNOSTIC TROUBLE CODE CHART [10/2024 - ]

Result:

See step 2

CHECK BATTERY VOLTAGE SENSOR (IGCT VOLTAGE)

WARNING:

Be sure to wear insulated gloves.

Pre-procedure1

Check that the service plug grip is not installed.
NOTE:
After removing the service plug grip, do not turn the ignition switch to ON (READY), unless instructed by the appropriate service information because this may cause a malfunction.
Connect the cable to the negative (-) auxiliary battery terminal.

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

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Component with harness connected (Battery Voltage Sensor)

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
z34-1 (IGCT) - z34-7 (GND)	Ignition switch ON	11 to 14 V	V

NOTE:

Turning the ignition switch to ON with the service plug grip removed causes other DTCs to be stored. Clear the DTCs after performing this inspection.

HINT:

As there might be an intermittent malfunction in the battery voltage sensor power source circuit, inspect the following even if the measured voltage is as specified:

Installation condition of fuse(s) (before removing fuse(s)) (IGCT circuit)
Fuse condition (before and after removing fuse(s)) (IGCT circuit)
Connection condition of connectors (IGCT circuit)
Wire harness condition (IGCT circuit)
Wire harness condition (GND circuit)

Result

Proceed to
OK
NG

Post-procedure1

Turn the ignition switch off.
Disconnect the cable from the negative (-) auxiliary battery terminal.

Result:

GO TO CAN COMMUNICATION SYSTEM. Refer to HOW TO PROCEED WITH TROUBLESHOOTING [10/2022 - 08/2023] , or refer to HOW TO PROCEED WITH TROUBLESHOOTING [08/2023 - ]

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY VOLTAGE SENSOR POWER SOURCE CIRCUIT)