Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc b177d ignition power supply low voltage

Subaru Legacy BN/BS (2015-2019) Service Manual / Occupant detection system (diagnostics) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc b177d ignition power supply low voltage

DTC DETECTING CONDITION:

• Power supply voltage of occupant detection control module is faulty.

• Occupant detection control module is faulty.

• Seat harness circuit is open, shorted or shorted to ground.

CAUTION:

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

WIRING DIAGRAM:

NOTE:

For the coupling connector, refer to “WIRING SYSTEM”.

Occupant detection system Occupant Detection System > WIRING DIAGRAM

STEP	CHECK	YES	NO
1.CHECK BATTERY VOLTAGE. Measure the battery voltage.	Is the battery voltage 8 V or less-	Check the battery. Battery > INSPECTION Battery > INSPECTION	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC B177D IGNITION POWER SUPPLY LOW VOLTAGE
2.CHECK FUSE. Check the fuse. (F/B fuse No. 20)	Is the fuse OK-	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC B177D IGNITION POWER SUPPLY LOW VOLTAGE	Replace the fuse. If the replaced fuse blows out easily, repair the ground short circuit in the harness between the battery and occupant detection CM.
3.CHECK POOR CONTACT OF CONNECTORS. Check for poor contact of the connectors between the occupant detection control module and airbag control module.	Is there poor contact-	When the connector is not fully connected, reconnect the connector correctly. Replace the faulty harness if the connector is faulty. (Replace the airbag rear harness along with body harness, or replace the occupant detection harness (seat harness).)	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC B177D IGNITION POWER SUPPLY LOW VOLTAGE
4.CHECK AIRBAG REAR HARNESS. 1) Turn the ignition switch to OFF, disconnect the battery ground cable, and wait for 60 seconds or more. 2) Disconnect the connectors (AB59) and (AB53) under the passenger’s seat. 3) Turn the ignition switch to ON. 4) Measure the voltage between connector (AB53) and chassis ground. CAUTION: Connect terminal (1AW) in the test harness AW to connector (AB53) terminal, and apply the tester to terminal (2AW). Connector & terminal (AB53) No. 6 (+) — Chassis ground (−):	Is the voltage 8 V or more-	Replace the occupant detection harness (seat harness). If defective is not improved, replace the occupant detection system (seat cushion & frame assembly) Front Seat > DISASSEMBLY, and then the airbag control module Airbag Control Module > REMOVAL in this order.	Replace the airbag rear harness along with body harness.

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Other materials:

Stopping engine
Stop the vehicle completely. Move the select lever to the "P" position. Press the push-button ignition switch. The engine will stop, and the power will be switched off WARNING Do not touch the push-button ignition switch during driving. When the p ...