DTC B27A8: Trunk/Rear Gate External Antenna Open

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.

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 trunk opener switch.)

Wiring diagram:

Keyless access with push button start system Ref. to WIRING SYSTEM>KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

For replacement procedure of keyless access control module, refer to the "REGISTRATION MANUAL FOR IMMOBILIZER" provided as a separate volume.
Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to KEYLESS ACCESS WITH PUSH BUTTON START (DIAGNOSTICS)>GENERAL DESCRIPTION>CAUTION

CHECK LAN SYSTEM .
Perform the diagnosis for 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.
CHECK CONNECTOR .
1. Disconnect the connector from the keyless access control module.
2. Disconnect the connector from the rear exterior antenna.
3. Check the connector.
Is the check result OK?

Yes : Go to 3.

No : Repair or replace the connector.
CHECK POWER SUPPLY CIRCUIT .
Using a tester, measure the voltage between the keyless access control module connector and chassis ground.

Connector & terminal

(i91) No. 4 (+) - Chassis ground (-):

Is the voltage 9.5 - 16 V?

Yes : Go to 4.

No : Check the power supply circuit.
CHECK HARNESS (OPEN CIRCUIT) .
Using a tester, measure the resistance between the keyless access control module connector and rear exterior antenna connector, and between keyless access control module connector and chassis ground.

Connector & terminal

(i92) No. 8 - (R116) No. 1:

(i92) No. 7 - (R116) No. 2:

(i92) No. 17 - Chassis ground:

(i91) No. 20 - Chassis ground:

Is the resistance less than 1 Ω?

Yes : Go to 5.

No : Repair or replace the open circuit of harness.
CHECK HARNESS (GROUND SHORT CIRCUIT) .
Using a tester, measure the resistance between the keyless access control module connector and chassis ground.

Connector & terminal

(i92) No. 8 - Chassis ground:

(i92) No. 7 - Chassis ground:

Is the resistance 10 kΩ or more?

Yes : Go to 6.

No : Repair or replace the short circuit of the harness.
CHECK DTC .
1. Connect the disconnected connectors.
2. Turn the ignition switch to ON.
3. Using the Subaru Select Monitor, perform the clear memory of [Keyless Access with Push Button Start (Collation)]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
4. Read the DTC of [Keyless Access with Push Button Start (Collation)] using the Subaru Select Monitor. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
Is DTC B27A8 displayed? (Current code)

Yes : Go to 7.

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.
CHECK KEYLESS ACCESS CONTROL MODULE .
1. Turn the ignition switch to OFF.
2. Short the terminals of the rear exterior antenna connector (R116).
  Connector & terminal
  
  (R116) No. 1 - (R116) No. 2:
3. Turn the ignition switch to ON.
4. Using the Subaru Select Monitor, perform the clear memory of [Keyless Access with Push Button Start (Collation)]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
5. Read the DTC of [Keyless Access with Push Button Start (Collation)] using the Subaru Select Monitor. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
Is DTC B27A8 displayed? (Current code)

Yes : Replace the keyless access control module. Ref. to SECURITY AND LOCKS>KEYLESS ACCESS CONTROL MODULE>REMOVAL

No : Malfunction occurred in the rear external antenna.