Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc b1878 short in front seat cushion airbag lh (to +b)

Subaru Legacy BN/BS (2015-2019) Service Manual / Airbag system (diagnostics) / Diagnostic chart with trouble code / Dtc b1878 short in front seat cushion airbag lh (to +b)

DIAGNOSIS START CONDITION:

Ignition voltage is 10 V to 16 V.

DTC DETECTING CONDITION:

Short circuit failure in power supply (shorted in main harness power supply, shorted in front seat cushion airbag LH power supply, shorted in airbag CM internal circuit power supply)

CAUTION:

Before performing diagnosis, refer to “CAUTION” in “General Description”. General Description > CAUTION

WIRING DIAGRAM:

Airbag system Airbag System > WIRING DIAGRAM

STEP	CHECK	YES	NO
1.CHECK POOR CONTACT OF CONNECTORS. Check for poor contact of the connectors between the airbag control module and the seat cushion airbag module LH.	Is there poor contact-	Replace the airbag rear harness along with body harness.	Diagnostic Chart with Trouble Code > DTC B1878 SHORT IN FRONT SEAT CUSHION AIRBAG LH (TO +B)
2.CHECK SEAT CUSHION AIRBAG MODULE. 1) Turn the ignition switch to OFF, disconnect the battery ground cable, and wait for 60 seconds or more. 2) Disconnect the connector (AB5) from the seat cushion airbag module LH, and connect the connector (1D) in the test harness D to connector (AB5). 3) Connect the airbag resistor to connector (3D) in the test harness D. 4) Connect the battery ground terminal and turn the ignition switch to ON.	Does the airbag warning light illuminate for six seconds and go off-	Replace the seat cushion airbag module LH. Seat Cushion Airbag Module	Diagnostic Chart with Trouble Code > DTC B1878 SHORT IN FRONT SEAT CUSHION AIRBAG LH (TO +B)
3.CHECK AIRBAG REAR HARNESS (SEAT CUSHION AIRBAG MODULE HARNESS LH) (SHORTED TO POWER SUPPLY). 1) Turn the ignition switch to OFF, disconnect the battery ground cable, and wait for 60 seconds or more. 2) Disconnect the connector (AB21) from seat belt pretensioner LH. 3) Disconnect the connector (AB19) of the side airbag module LH. 4) Disconnect the connector (AB31) from curtain airbag module LH. 5) Disconnect the airbag resistor from test harness D. 6) Disconnect the connectors (AB6, AB17, AB18) from airbag control module. 7) Connect the connector (1AD) in test harness AD AV to the connectors (AB6, AB17, AB18). 8) Connect the connector (2AD) in test harness AD AV and the connector (1AG) in test harness AG. 9) Connect the battery ground terminal and turn the ignition switch to ON. 10) Measure the voltage between connector (3D) in the test harness D and chassis ground. Connector & terminal (3D) No. 4 (+) — Chassis ground (−): (3D) No. 3 (+) — Chassis ground (−):	Is the voltage less than 1 V-	Diagnostic Chart with Trouble Code > DTC B1828 SHORT IN SIDE AIRBAG LH (TO +B)	Replace the airbag rear harness along with body harness.
4.CHECK AIRBAG CONTROL MODULE. 1) Connect all connectors. 2) Clear the memory. Clear Memory Mode 3) Perform the Inspection Mode. Inspection Mode 4) Read the DTC. (Current malfunction) Read Diagnostic Trouble Code (DTC)	Is DTC B1878 displayed-	Replace the airbag control module. Airbag Control Module	Diagnostic Chart with Trouble Code > DTC B1878 SHORT IN FRONT SEAT CUSHION AIRBAG LH (TO +B)
5.CHECK FOR ANY OTHER DTC ON DISPLAY. Read the DTC. (Current malfunction) Read Diagnostic Trouble Code (DTC)	Is any other DTC displayed-	Check DTC using “List of Diagnostic Trouble Code (DTC)”. List of Diagnostic Trouble Code (DTC)	Finish the diagnosis.

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DIAGNOSIS START CONDITION:Ignition voltage is 10 V to 16 V.DTC DETECTING CONDITION:Short circuit between front seat cushion airbag LH circuit and other circuitCAUTION:Before performing diagnosis, refe ...

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