DTC B278A: Push Engine Switch Power Supply Circuit

DTC detecting condition: 

Transponder power supply (VC5 terminal) short circuit to ground upon the transponder collation start operation.

(Short circuit to ground is determined when transponder power supply (VC5 terminal) output level is judged as "L" level while monitored in the keyless access control module when the transponder power supply (VC5 terminal) outputs "H" level.)

Trouble symptom: 

Engine does not start even when the access key is pointed toward the vehicle.

Wiring diagram: 

Immobilizer system. Refer 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. Using an oscilloscope, measure the waveform between he push button ignition switch connectors. (Waveform within 30 seconds after the push button ignition switch is pressed)

      Connector & terminal 

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

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      Is the waveform shown in the left column displayed?

      Yes:  Replace the push button ignition switch. Refer to SECURITY AND LOCKS>PUSH BUTTON IGNITION SWITCH .

      No:  Go to  2.

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. 21:

      (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. 21 - 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. Perform the clear memory for «Keyless Access with Push Button Start» using the Subaru Select Monitor. Refer to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>CLEAR MEMORY .
   2. Read DTCs of «Keyless Access with Push Button Start» using the Subaru Select Monitor. Refer to KEYLESS ACCESS WITH PUSH BUTTON START SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

      Is DTC B278A displayed? (Current malfunction)

      Yes:  Replace the keyless access control module. Refer 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.