Lexus TechDoc

DTC U029A-123 Lost Communication with Hybrid Battery Pack Sensor Module

for Preparation Click here

DESCRIPTION

The battery smart unit detects the HV battery conditions (voltage, current, and temperature) and the battery cooling fan voltage, and sends the detected signals to the power management control ECU via the serial communication system.

DTC No.	DTC Detection Condition	Trouble Area
U029A-123	Problem in serial communication between the battery smart unit and power management control ECU (1 trip detection)	Wire harness or connector Power management control ECU Battery smart unit

WIRING DIAGRAM

INSPECTION PROCEDURE

CAUTION:

If the battery cover is removed, install it before turning the power switch on (IG) or (READY). If the power switch is turned on (IG) or (READY) with the battery cover removed, U029A-123 may be set.
Before inspecting the high-voltage system, take safety precautions to prevent electrical shocks, such as wearing insulated gloves and removing the service plug grip. After removing the service plug grip, put it in your pocket to prevent other technicians from accidentally reconnecting it while you are working on the high-voltage system.
After removing the service plug grip, wait for at least 10 minutes before touching any of the high-voltage connectors or terminals. After waiting for 10 minutes, check the voltage at the terminals in the inspection point in the inverter with converter assembly. The voltage should be 0 V before beginning work (Click here).

HINT:

Waiting for at least 10 minutes is required to discharge the high-voltage capacitor inside the inverter with converter assembly.

NOTICE:

After turning the power switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) auxiliary battery terminal notices before proceeding with work (Click here).

1.CHECK DTC OUTPUT (HV)

Connect the intelligent tester to the DLC3.

Turn the power switch on (IG).

Enter the following menus: Powertrain / Hybrid Control / DTC.

Check for DTCs (Click here).
Result:
Result
Proceed to
Only U029A-123 is output.
A
DTCs other than U029A-123 are also output.
B

Disconnect the intelligent tester from the DLC3.

GO TO DTC CHART (Click here)

A

2.CHECK HARNESS AND CONNECTOR (POWER MANAGEMENT CONTROL ECU - BATTERY SMART UNIT)

CAUTION:

Be sure to wear insulated gloves.

Disconnect the cable from the negative (-) battery terminal of the auxiliary battery.

Check that the service plug grip is not installed.
NOTICE:
After removing the service plug grip, do not turn the power switch on (READY), unless instructed by the repair manual because this may cause a malfunction.

Disconnect connector H3 from the power management control ECU (Click here).

Disconnect connector i1 from the battery smart unit.

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

Standard Resistance:

Tester Connection	Switch Condition	Specified Condition
H3-32 (BTH+) - i1-2 (BTH+)	Power switch off	Below 1 Ω
H3-33 (BTH-) - i1-3 (BTH-)	Power switch off	Below 1 Ω
i1-2 (BTH+) - i1-8 (GND) and Body ground	Power switch off	10 kΩ or higher
i1-3 (BTH-) - i1-8 (GND) and Body ground	Power switch off	10 kΩ or higher

Text in Illustration
*a	Rear view of wire harness connector (to Power Management Control ECU)
*b	Rear view of wire harness connector (to Battery Smart Unit)

Remove the IGCT No. 2 fuse and AM2 fuse from the engine room junction block assembly.
Text in Illustration
*1
Engine Room Junction Block Assembly
*2
AM2 Fuse
*3
IGCT No. 2 Fuse

Text in Illustration
*1	Engine Room Junction Block Assembly
*2	AM2 Fuse
*3	IGCT No. 2 Fuse

Disconnect all connectors from the power management control ECU.

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

Standard Resistance:

Tester Connection	Switch Condition	Specified Condition
H3-32 (BTH+) - H4-7 (AM21)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - H3-1 (AM22)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A19-2 (+B2)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A20-5 (+B1)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A20-6 (MREL)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A20-1 (IG2)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - H4-1 (ACCD)	Power switch off	10 kΩ or higher
H3-32 (BTH+) H4-2 (IG1D)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A20-2 (IG2D)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A19-4 (FCTL)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - H3-14 (SPDI)	Power switch off	10 kΩ or higher
H3-32 (BTH+) - A19-16 (GI)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - H4-7 (AM21)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - H3-1 (AM22)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A19-2 (+B2)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A20-5 (+B1)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A20-6 (MREL)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A20-1 (IG2)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - H4-1 (ACCD)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - H4-2 (IG1D)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A20-2 (IG2D)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - H3-14 (SPDI)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A19-4 (FCTL)	Power switch off	10 kΩ or higher
H3-33 (BTH-) - A19-16 (GI)	Power switch off	10 kΩ or higher

Text in Illustration
*a	Rear view of wire harness connector (to Power Management Control ECU)	-	-

NOTICE:

When taking a measurement with a tester, do not apply excessive force to the tester probe to avoid damaging the holder.

Connect the cable to the negative (-) battery terminal of the auxiliary battery.

Connect the battery smart unit connector.

Connect the power management control ECU connectors (Click here).

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

3.CHECK POWER MANAGEMENT CONTROL ECU

CAUTION:

Be sure to wear insulated gloves.

Check that the service plug grip is not installed.
NOTICE:
After removing the service plug grip, do not turn the power switch on (READY), unless instructed by the repair manual because this may cause a malfunction.

Disconnect connector i1 from the battery smart unit.

Turn the power switch on (IG).

Measure the voltage according to the value(s) in the table below.
NOTICE:
Turning the power switch on (IG) with the service plug grip removed causes an interlock switch system DTC to be set. Use the intelligent tester to clear the DTCs (Click here).
Standard Voltage:
Tester Connection
Switch Condition
Specified Condition
i1-2 (BTH+) - i1-8 (GND)
Power switch on (IG)
2.3 to 2.7 V
i1-3 (BTH-) - i1-8 (GND)
Power switch on (IG)
2.3 to 2.7 V
Text in Illustration
*a
Rear view of wire harness connector
(to Battery Smart Unit)

Text in Illustration
*a	Rear view of wire harness connector (to Battery Smart Unit)

Turn the power switch off.

Measure the resistance according to the value(s) in the table below.
Standard Resistance:
Tester Connection
Switch Condition
Specified Condition
i1-2 (BTH+) - i1-3 (BTH-)
Power switch off
4.4 to 5.4 kΩ
Text in Illustration
*a
Rear view of wire harness connector
(to Battery Smart Unit)
HINT:
Resistance becomes 2.0 kΩ or less when there is a short circuit in the power management control ECU.

Text in Illustration
*a	Rear view of wire harness connector (to Battery Smart Unit)

Connect the battery smart unit connector.

REPLACE POWER MANAGEMENT CONTROL ECU (Click here)

REPLACE BATTERY SMART UNIT (Click here)

Result	Proceed to
Only U029A-123 is output.	A
DTCs other than U029A-123 are also output.	B