Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Engine Immobiliser System Circuit Short to Battery (B279A12)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Interior / Theft Deterrent / Keyless Entry / Immobiliser System / 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 engine switch on (IG) 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 Techstream with the engine switch off, connect the Techstream to the DLC3 and turn a courtesy light switch on and off at intervals of 1.5 seconds or less until communication between the Techstream and the vehicle begins. Then select the vehicle type under manual mode and enter the following menus: Body Electrical / Smart Access. While using the Techstream, periodically turn a courtesy light switch on and off at intervals of 1.5 seconds or less to maintain communication between the Techstream and the vehicle.
  • Before replacing the ECM or ID code box (immobiliser code ECU), refer to Registration.

    Click here

  • After performing repairs, confirm that no DTCs are output by performing "DTC Output Confirmation Operation".

HINT:

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

PROCEDURE

1.

CLEAR DTC

(a) Clear the DTCs.

Powertrain > Engine > Clear DTCs
NEXT

2.

CHECK FOR DTC

(a) Turn the engine switch on (IG) and wait 10 seconds.

(b) Check for DTCs.

Powertrain > Engine > Trouble Codes

HINT:

If DTCs other than DTC B279A12 are output, troubleshoot those DTCs first.

Result

Proceed to

Only DTC B279A12 is output

A

DTC B279A12 and other DTCs are output

B
B

GO TO DIAGNOSTIC TROUBLE CODE CHART

A

3.

CHECK CONNECTION OF CONNECTOR

(a) Turn the engine 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.

NG

CONNECT CONNECTORS PROPERLY
OK

4.

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

(a) Disconnect the J36 ID code box (immobiliser code ECU) connector.

(b) Disconnect the A37 ECM connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J36-4 (EFIO) - A37-59 (IMI)

Always

Below 1 Ω

J36-4 (EFIO) or A37-59 (IMI) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

5.

REPLACE ID CODE BOX (IMMOBILISER CODE ECU)

(a) Replace the ID code box (immobiliser code ECU) with a new one.

Click here

NEXT

6.

REGISTER ECU COMMUNICATION ID

(a) Register the ECU communication ID code.

Click here

NEXT

7.

CHECK WHETHER ENGINE STARTS

(a) Check that the engine starts.

OK:

Engine starts normally.

NG

REPLACE ECM

OK

8.

CLEAR DTC

(a) Clear the DTCs.

Powertrain > Engine > Clear DTCs
NEXT

9.

CHECK FOR DTC

(a) Perform "DTC Output Confirmation Operation" procedure.

(b) Check for DTCs.

Powertrain > Engine > Trouble Codes

OK:

DTC B279A12 is not output.

OK

END (ID CODE BOX (IMMOBILISER CODE ECU) WAS DEFECTIVE)
NG

REPLACE ECM

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