Dtc B2278 Engine Switch Circuit Malfunction
Lexus IS250 IS220d GSE20 ALE20 2AD-FHV STARTING
DESCRIPTION
WIRING DIAGRAM
INSPECTION PROCEDURE
CHECK CONNECTORS
CHECK HARNESS AND CONNECTOR (POWER SOURCE CONTROL ECU -BODY GROUND)
INSPECT ENGINE SWITCH
CHECK WIRE HARNESS (ENGINE SWITCH - POWER SOURCE CONTROL ECU AND BODY GROUND)
READ VALUE OF INTELLIGENT TESTER (START SWITCH 1 AND 2)
RECHECK FOR DTC
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.
- When the power source control ECU is replaced with a new one and the negative (-) battery terminal is connected, the power source mode becomes the IG-ON mode. When the battery is removed and reinstalled, the power source mode that was selected when the battery was removed is restored.
| DTC No. | DTC Detection Condition | Trouble Area |
| B2278 |
Communication is abnormal between the power source control ECU and engine switch or the engine switch is defective |
Engine switch
Power source control ECU
Wire harness or connector
|
WIRING DIAGRAM
INSPECTION PROCEDURE
Check that the connectors are securely connected and the terminals are not deformed or loose.
- OK:
- The connectors are securely connected and the terminals are not deformed or loose.
| | REPAIR OR REPLACE CONNECTORS |
|
|
| 2.CHECK HARNESS AND CONNECTOR (POWER SOURCE CONTROL ECU -BODY GROUND) |
Disconnect the J55 ECU connector.
Measure the resistance according to the value(s) in the table below.
- Standard resistance:
| Tester Connection (Symbols) | Condition | Specified Condition |
| J55-6 (GND2) - Body ground | Always | Below 1 Ω |
| | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
|
Remove the engine switch.
Disconnect the switch connector.
Measure the resistance according to the value(s) in the table below.
- Standard resistance:
Tester Connection
(Symbols) | 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 |
- This switch is a momentary type switch.
| 4.CHECK WIRE HARNESS (ENGINE SWITCH - POWER SOURCE CONTROL ECU AND BODY GROUND) |
Measure the resistance according to the value(s) in the table below.
- Standard resistance:
| Tester Connection (Symbols) | Condition | Specified Condition |
| J31-7 (SS1) - J55-14 (SSW1) | Always | Below 1 Ω |
| J31-2 (SS2) - J55-37 (SSW2) | Always | Below 1 Ω |
| J31-5 (GND) - Body ground | Always | Below 1 Ω |
| J31-7 (SS1) or J55-14 (SSW1) - Body ground | Always | 10 kΩ or higher |
| J31-2 (SS2) or J55-37 (SSW2) - Body ground | Always | 10 kΩ or higher |
| | REPAIR OR REPLACE HARNESS OR CONNECTOR |
|
|
| 5.READ VALUE OF INTELLIGENT TESTER (START SWITCH 1 AND 2) |
Reconnect the connectors.
Connect the intelligent tester to the DLC3.
Turn the engine switch on (IG).
Check the DATA LIST for proper functioning of the start switches 1 and 2.
Power Source Control:| 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 SW2 | Start Switch 2/ ON or OFF | ON: Engine switch on (IG)
OFF: Engine switch OFF | - |
- OK:
- ON (engine switch on (IG)) and OFF (engine switch off) appear on the screen.
| | REPLACE POWER SOURCE CONTROL ECU |
|
|
Check for DTCs again.
- OK:
- DTC B2278 is not output.
| | REPLACE POWER SOURCE CONTROL ECU |
|
|
| OK | |
| |
| CHECK INTERMITTENT PROBLEMS |
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LEXUS IS250, IS220d / GSE20 ALE20
