Dtc B2278 Engine Switch Circuit Malfunction

Engine. Lexus Gs430, Gs300. Uzs190 Grs190
3Gr-Fse Starting. Lexus Gs430, Gs300. Uzs190 Grs190

DESCRIPTION

WIRING DIAGRAM

INSPECTION PROCEDURE

READ VALUE OF INTELLIGENT TESTER (START SWITCH 1 and 2)

INSPECT ENGINE SWITCH

CHECK WIRE HARNESS (ENGINE SWITCH - POWER SOURCE CONTROL ECU AND BODY GROUND)

DTC B2278 Engine Switch Circuit Malfunction


DESCRIPTION

This DTC is output when 1) a malfunction is detected between the power source control ECU and the engine switch; or 2) either of the switches inside the engine switch is malfunctioning.

DTC No.
DTC Detection Condition
Trouble Area
B2278
Communication is abnormal between power source control ECU and engine switch or engine switch is defective
  1. Power source control ECU
  2. Engine switch
  3. Wire harness

WIRING DIAGRAM


Lexus Gs430, Gs300. Uzs190 Grs190.3Gr-Fse Starting.Starting System. Dtc B2278 Engine Switch Circuit Malfunction


INSPECTION PROCEDURE

1.READ VALUE OF INTELLIGENT TESTER (START SWITCH 1 and 2)

  1. Check the Data List for proper functioning of the start switch 1 and 2.

    Power source control ECU
    Item
    		Measurement Item/Display (Range)
    		Normal Condition
    		Diagnostic Note
    St SW1
    		Start Switch 1/ ON or OFF
    		ON: Engine switch on (IG)
    OFF: Engine switch OFF
    		-
    St SW 2
    		Start Switch 2/ ON or OFF
    		ON: Engine switch on (IG)
    OFF: Engine switch OFF
    		-
    OK:
    ON (engine switch on (IG)) appears on the screen.


NG
Go to step 2
OK

REPLACE POWER SOURCE CONTROL ECU

2.INSPECT ENGINE SWITCH
Lexus Gs430, Gs300. Uzs190 Grs190.3Gr-Fse Starting.Starting System. Dtc B2278 Engine Switch Circuit Malfunction

  1. Remove the engine switch.

  1. Measure the resistance of the switch.

    Standard resistance:
    Tester Connection
    		Switch Condition
    		Specified Condition
    7 (SS1) - 5 (GND)
    		Pushed
    		Below 1 Ω
    2 (SS2) - 5 (GND)
    		Pushed
    		Below 1 Ω
    7 (SS1) - 5 (GND)
    		Not pushed
    		10 kΩ or higher
    2 (SS2) - 5 (GND)
    		Not pushed
    		10 kΩ or higher


NG
REPLACE ENGINE SWITCH
OK


3.CHECK WIRE HARNESS (ENGINE SWITCH - POWER SOURCE CONTROL ECU AND BODY GROUND)
Lexus Gs430, Gs300. Uzs190 Grs190.3Gr-Fse Starting.Starting System. Dtc B2278 Engine Switch Circuit Malfunction

  1. Disconnect the L29 switch connector.

  1. Disconnect the L73 ECU connector.

  1. Measure the resistance of the wire harness side connectors.

    Standard resistance:
    Tester Connection
    		Specified Condition
    L29-7 (SS1) - L73-14 (SSW1)
    		Below 1 Ω
    L29-2 (SS2) - L73-37 (SSW2)
    		Below 1 Ω
    L29-5 (GND) - Body ground
    		Below 1 Ω
    L29-7 (SS1) or L73-14 (SSW1) - Body ground
    		10 kΩ or higher
    L29-2 (SS2) or L73-37 (SSW2) - Body ground
    		10 kΩ or higher


NG
REPAIR OR REPLACE HARNESS AND CONNECTOR
OK

REPLACE POWER SOURCE CONTROL ECU