Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc b1908 short in front p/t lh (to +b)

Subaru Legacy BN/BS (2015-2019) Service Manual / Airbag system (diagnostics) / Diagnostic chart with trouble code / Dtc b1908 short in front p/t 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 rear harness power supply, shorted in front seat pretensioner 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 belt pretensioner LH.	Is there poor contact-	Replace the airbag rear harness along with body harness.	Diagnostic Chart with Trouble Code > DTC B1908 SHORT IN FRONT P/T LH (TO +B)
2.CHECK SEAT BELT PRETENSIONER. 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) Connect the connector (1N) in the test harness N to the connector (AB21). 4) Connect the airbag resistor to the connector (2N) of test harness N. 5) 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 belt pretensioner LH. Front Seat Belt	Diagnostic Chart with Trouble Code > DTC B1908 SHORT IN FRONT P/T LH (TO +B)
3.CHECK AIRBAG REAR HARNESS (PRETENSIONER 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 airbag resistor from the connector (2N) of test harness N. 3) Disconnect the connector (AB5) from seat cushion airbag module LH. 4) Disconnect the connector (AB19) from side airbag module LH. 5) Disconnect the connector (AB31) from curtain airbag module LH. 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 (3AG) in the test harness AG and chassis ground. Connector & terminal (3AG) No. 18 (+) — Chassis ground (−): (3AG) No. 20 (+) — Chassis ground (−):	Is the voltage less than 1 V-	Diagnostic Chart with Trouble Code > DTC B1908 SHORT IN FRONT P/T 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 B1908 displayed-	Replace the airbag control module. Airbag Control Module	Diagnostic Chart with Trouble Code > DTC B1908 SHORT IN FRONT P/T 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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