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DTC B27A8: Trunk/Rear Gate External Antenna Open

DTC detecting condition: 

When open circuit occurs in the harness between keyless access CONTROL MODULE and rear exterior antenna.

Trouble symptom: 

Keyless access system does not function.

(Cannot unlock using rear gate opener button.)

CAUTION: For replacement procedure of keyless access CONTROL MODULE, refer to the "REGISTRATION MANUAL FOR IMMOBILIZER" provided as a separate volume. Contact an Authorized Subaru Dealership.

Wiring diagram: 

Keyless access system Ref. to WIRING SYSTEM>Keyless Access System>WIRING DIAGRAM

G10271486Courtesy of SUBARU OF AMERICA, INC.
  1. CHECK LAN SYSTEM  .

    Inspect LAN system. Ref. to LAN SYSTEM (DIAGNOSTICS)>Basic Diagnostic Procedure>PROCEDURE

    Is the check result OK?

    Yes: Go to  2

    No: Perform the inspection according to the diagnosis for LAN system.

  2. CHECK CONNECTOR  .
    1. Disconnect the keyless access CONTROL MODULE connector.
    2. Disconnect the rear exterior antenna connector.
    3. Check the connector.

    Is the check result OK?

    Yes: Go to  3

    No: Repair or replace the connector.

  3. CHECK HARNESS (OPEN CIRCUIT)  .

    Using a tester, measure the resistance between the keyless access CONTROL MODULE connector and rear external antenna connector.

    Connector & terminal 

    (B573) No. 2 - (R299) No. 1:

    (B573) No. 1 - (R299) No. 2:

    Is the resistance less than 1 Ω?

    Yes: Go to  4

    No: Repair or replace the open circuit of harness.

  4. CHECK HARNESS (GROUND SHORT CIRCUIT)  .

    Using a tester, measure the resistance between the keyless access CONTROL MODULE connector and chassis ground.

    Connector & terminal 

    (B573) No. 2 - Chassis ground:

    (B573) No. 1 - Chassis ground:

    Is the resistance 10 kΩ or more?

    Yes: Go to  5

    No: Repair or replace the short circuit of the harness.

  5. CHECK DTC  .
    1. Connect the keyless access CONTROL MODULE connector.
    2. Using the Subaru Select Monitor, clear the memory. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Clear Memory Mode 
    3. Read the DTC using Subaru Select Monitor. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) 

    Is DTC B27A8 displayed?

    Yes: Go to  6

    No: Even if DTC is displayed, the circuit has returned to a normal condition at this time. Reproduce the failure, and then perform the diagnosis again.

    NOTE: In this case, temporary poor contact of connector, temporary open or short circuit of harness may be the cause.
  6. CHECK REAR EXTERIOR ANTENNA  .
    1. Replace the rear exterior antenna with the rear interior antenna. Ref. to SECURITY AND LOCKS>Keyless Access Indoor Antenna . Ref. to SECURITY AND LOCKS>Keyless Access Outdoor Antenna
    2. Using the Subaru Select Monitor, clear the memory. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Clear Memory Mode 
    3. Read the DTC using Subaru Select Monitor. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) 

    Is DTC B27A8 displayed?

    Yes: Replace the keyless access CONTROL MODULE. Ref. to SECURITY AND LOCKS>Keyless Access CONTROL MODULE

    No: Malfunction occurred in the rear external antenna.

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