DTC B279A-12: Engine Immobilizer System Circuit Short to Battery [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 CONNECTION OF CONNECTOR

Pre-procedure1

Turn the ignition switch off.

Check that the connectors are properly connected to the ECM and ID code box (immobilizer code ECU).

Connectors are properly connected.

Result

Proceed to
OK
NG

Post-procedure1

None

Result:

CONNECT CONNECTORS PROPERLY

Result:

See step 2

CHECK WHETHER ENGINE STARTS

Check that the engine starts.

Engine starts normally.

Result

Proceed to
OK
NG

Result:

USE SIMULATION METHOD TO CHECK. Refer to HOW TO PROCEED WITH TROUBLESHOOTING [10/2022 - ]

Result:

See step 3

CHECK ECM (TERMINAL EFIO)

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

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Component with harness connected (ID Code Box (Immobilizer Code ECU))

Standard Voltage

Tester Connection	Condition	Specified Condition	Result
C54-4 (EFIO) - Body ground	Ignition switch ON	11 to 14 V	V

Result

Proceed to
OK
NG

Result:

See step 5

Result:

See step 4

CHECK ID CODE BOX (IMMOBILIZER CODE ECU) (TERMINAL EFIO)

Using an oscilloscope, check the waveform.

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*a	Component with harness connected ID Code Box (Immobilizer Code ECU)	*b	Waveform
*c	Approximately 160 ms.	*d	Approximately 270 ms.

Tester Connection	Condition	Tool Setting	Specified Condition
C54-4 (EFIO) - Body ground	Within 3 seconds of engine start or within 3 seconds of ignition switch turned to ON after cable disconnected and reconnected to auxiliary battery	2 V/DIV., 500 ms./DIV.	Pulse generation (See waveform)

Result

Proceed to
OK
NG

Result:

REPLACE ECM. Refer to REMOVAL [10/2022 - ]

Result:

REPLACE ID CODE BOX (IMMOBILIZER CODE ECU). Refer to REMOVAL [10/2022 - 08/2023] , or refer to REMOVAL [08/2023 - ]

CHECK HARNESS AND CONNECTOR (ID CODE BOX (IMMOBILIZER CODE ECU) - ECM)

Pre-procedure1

Disconnect the A16 ECM connector.
Disconnect the C54 ID code box (immobilizer code ECU) connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition	Result
C54-4 (EFIO) - A16-38 (IMI)	Always	Below 1 Ω	Ω

Result

Proceed to
OK
NG

Post-procedure1

None

Result:

REPLACE ECM. Refer to REMOVAL [10/2022 - ]

Result:

REPAIR OR REPLACE HARNESS OR CONNECTOR