DTC B278A: Short to GND in Immobiliser System Power Source Circuit [08/2013 - ]: Procedure

WARNING: This page is about a different car, the 2014 Lexus ES 300h. However, it is still accessible from the selected car via links, so may be relevant.

CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - POWER SWITCH)

Disconnect the H57 and H58 certification ECU (smart key ECU assembly) connectors.
Disconnect the H44 power switch connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
H58-9 (VC5) - H44-10 (VC5)	Always	Below 1 Ω
H57-6 (AGND) - H44-6 (AGND)	Always	Below 1 Ω
H44-10 (VC5) - Body ground	Always	10 kΩ or higher
H44-6 (AGND) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

Reconnect the H57 and H58 certification ECU (smart key ECU assembly) connectors.
Reconnect the H44 power switch connector.

Using an oscilloscope, check the waveform.

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

Perform this inspection on the power switch side.

MEASUREMENT CONDITION

Item	Content
Tester Connection	H44-10 (VC5) - H44-6 (AGND)
Tool Setting	2 V/DIV., 200 ms./DIV.
Condition	Power switch off, key not in cabin, within 30 seconds after power switch pressed

The waveform is similar to that shown in the illustration.

TEXT IN ILLUSTRATION

*a	Component with harness connected (Power Switch)

NG → See step 3

OK → See step 4

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY). Refer to REMOVAL [08/2013 - ]
REPLACE POWER SWITCH. Refer to REMOVAL [08/2013 - ]