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HOMESERVICE MANUALSSUBARU2005OUTBACK I, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - ENGINE (DIAGNOSTICS) (H4SO)DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)DTC P0448 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT SHORTED
2005 Subaru Outback i, Standard

DTC P0448 Evaporative Emission Control System Vent Control Circuit Shorted

2005 Subaru Outback i, StandardSECTION DTC P0448 Evaporative Emission Control System Vent Control Circuit Shorted

DTC DETECTING CONDITION: 

CAUTION: After repair or replacement of faulty parts, conduct CLEAR MEMORY MODE < Ref. to , OPERATION , Clear Memory Mode.> and INSPECTION MODE < Ref. to , PROCEDURE , Inspection Mode.>.

WIRING DIAGRAM: 

Fig 1: DTC P0448 Evaporative Emission Control System Vent Control Circuit Shorted
G03828485Courtesy of SUBARU OF AMERICA, INC.
DTC P0448 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT SHORTED DIAGNOSIS

Step Check Yes No
1. CHECK INPUT SIGNAL FOR ECM. 
  1. Turn ignition switch to OFF.
  2. Connect the test mode connector at the lower portion of instrument panel (on the driver's side).
  3. Turn ignition switch to ON.
  4. While operating the drain valve, measure voltage between ECM and chassis ground.
NOTE: Drain valve operation can be executed using Subaru Select Monitor. For the procedure, refer to COMPULSORY VALVE OPERATION CHECK MODE .

Connector & terminal 

(B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage 0 - 10 V? Go to step 2.  The malfunction indicator light may light up, however, the circuit is returned to the normal status at the moment. In this case, repair poor contact in ECM connector.
2. CHECK INPUT SIGNAL FOR ECM. 
  1. Turn ignition switch to ON.
  2. Measure the voltage between ECM and chassis ground.

    Connector & terminal 

    (B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage more than 10 V? Go to step 4.  Go to step 3. 
3. CHECK FOR POOR CONTACT. 

Check for poor contact in ECM connector.

 Is there poor contact in ECM connector? Repair poor contact in ECM connector. Replace the ECM. < Ref. to ENGINE CONTROL MODULE (ECM) . >
4. CHECK HARNESS BETWEEN DRAIN VALVE AND ECM CONNECTOR. 
  1. Turn ignition switch to OFF.
  2. Disconnect the connector from drain valve.
  3. Turn ignition switch to ON.
  4. Measure the voltage between ECM and chassis ground.

    Connector & terminal 

    (B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage more than 10 V? Repair short circuit to battery in harness between ECM and drain valve connector. After repair, replace the ECM. < Ref. to ENGINE CONTROL MODULE (ECM) . > Go to step 5. 
5. CHECK DRAIN VALVE. 
  1. Turn ignition switch to OFF.
  2. Measure the resistance between drain valve terminals.

    Terminals 

    No. 1 - No. 2: 

 Is the resistance less than 1 Ω? Replace the drain valve < Ref. to DRAIN VALVE . > and ECM < Ref. to ENGINE CONTROL MODULE (ECM) .>. Go to step 6. 
6. CHECK FOR POOR CONTACT. 

Check for poor contact in ECM connector.

 Is there poor contact in ECM connector? Repair poor contact in ECM connector. Replace the ECM. < Ref. to ENGINE CONTROL MODULE (ECM) . >
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.