Toyota Yaris: Smart Key System (for Start Function) / Engine Immobiliser System Circuit Short to Battery (B279A12)

Toyota Yaris XP210 (2020-2025) Reapir and Service Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Smart Key System (for Start Function) / Engine Immobiliser System Circuit Short to Battery (B279A12)

DESCRIPTION

If the communication line (IMI - EFIO) between the ECM and ID code box (immobiliser code ECU) is stuck high, the ECM will store this DTC.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Note
B279A12	Engine Immobiliser System Circuit Short to Battery	The communication line (IMI - EFIO) between the ECM and ID code box (immobiliser code ECU) is stuck high. (1 trip detection logic*)	ID code box (immobiliser code ECU) ECM Wire harness or connector	DTC output confirmation operation: Turn the ignition switch to ON and wait 6 seconds.

*: Only output while a malfunction is present.

Vehicle Condition and Fail-safe Operation when Malfunction Detected

Vehicle Condition when Malfunction Detected	Fail-safe Operation when Malfunction Detected
Engine cannot be started	Engine cannot be started

Related Data List and Active Test

DTC No.	Data List and Active Test
B279A12	-

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

When using the GTS with the ignition switch off, connect the GTS to the DLC3 and turn a courtesy light switch on and off at intervals of 1.5 seconds or less until communication between the GTS and the vehicle begins. Then select the vehicle type under manual mode and enter the following menus: Body Electrical / Smart Key. While using the GTS, periodically turn a courtesy light switch on and off at intervals of 1.5 seconds or less to maintain communication between the GTS and the vehicle.
The smart key system (for Start Function) uses the LIN communication system and CAN communication system. Inspect the communication function by following How to Proceed with Troubleshooting. Troubleshoot the smart key system (for Start Function) after confirming that the communication systems are functioning properly.
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Before replacing the ECM or ID code box (immobiliser code ECU), refer to the Registration.
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After performing repairs, confirm that no DTCs are output by performing "DTC Output Confirmation Operation".

HINT:

When DTC B279A12 and the certification ECU (smart key ECU assembly) DTC are output simultaneously, first perform troubleshooting for the certification ECU (smart key ECU assembly) DTC.

PROCEDURE

1.	CHECK CONNECTION OF CONNECTOR

(a) Turn the ignition switch off.

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

OK:

Connectors are properly connected.

CONNECT CONNECTORS PROPERLY

2.	CHECK ID CODE BOX (IMMOBILISER CODE ECU) (TERMINAL EFIO)

(a) Using an oscilloscope, check the waveform.

Component with harness connected

(ID Code Box (Immobiliser Code ECU))

Waveform

Approximately 160 ms.

Approximately 270 ms.

OK:

Tester Connection	Condition	Tool Setting	Specified Condition
H67-4 (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)

Tester Connection

Condition

Tool Setting

Specified Condition

H67-4 (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
11 to 14 V	A
Below 1 V	B
Normal wavform	C

REPLACE ID CODE BOX (IMMOBILISER CODE ECU)

REPLACE ECM

3.	CHECK HARNESS AND CONNECTOR (ID CODE BOX (IMMOBILISER CODE ECU) - ECM)

(a) Disconnect the A106 ECM connector.

(b) Disconnect the H67 ID code box (immobiliser code ECU) connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
A106-61 (IMI) - H67-4 (EFIO)	Always	Below 1 Ω

REPLACE ECM

REPAIR OR REPLACE HARNESS OR CONNECTOR

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