DTC B278A: Push Engine Switch Power Supply Circuit

DTC detecting condition: 

When the power supply circuit of the push button ignition switch is shorted to ground.

Trouble symptom: 

• Engine will not start.
• The keyless access system function does not operate.

Wiring diagram: 

Immobilizer system Ref. to WIRING SYSTEM>Immobilizer System>WIRING DIAGRAM

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1. CHECK KEYLESS ACCESS CONTROL MODULE  .
   1. Turn the ignition switch to OFF.
   2. Take the access key out of the passenger room.
   3. Push the push button ignition switch. Within 30 seconds, use oscilloscope to measure the waveform between connectors.

      Connector & terminal 

      (i150) No. 14 - (i150) No. 8:

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   Is a waveform displayed as indicated on the left?

   Yes: Go to  2

   No: Replace the push button ignition switch. Ref. to SECURITY AND LOCKS>Push Button Ignition Switch

2. CHECK HARNESS (OPEN CIRCUIT)  .
   1. Disconnect the keyless access CONTROL MODULE connector.
   2. Disconnect the push button ignition switch connector.
   3. Using a tester, measure the resistance between the push button ignition switch connector and the keyless access CONTROL MODULE connector.

      Connector & terminal 

      (i150) No. 14 - (B574) No. 1:

      (i150) No. 8 - (B574) No. 24:

   Is the resistance less than 1 Ω?

   Yes: Go to  3

   No: Repair or replace the open circuit of harness.

3. CHECK HARNESS (GROUND SHORT CIRCUIT)  .

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

   Connector & terminal 

   (B574) No. 1 - Chassis ground:

   (B574) No. 24 - Chassis ground:

   Is the resistance 10 kΩ or more?

   Yes: Go to  4

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

4. CHECK DTC  .
   1. Using the Subaru Select Monitor, clear the memory. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Clear Memory Mode 
   2. Read the DTC using Subaru Select Monitor. Ref. to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>Read Diagnostic Trouble Code (DTC) 

   Is DTC B278A displayed?

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

   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.