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DTC P0448: EVAP System Vent Control Circuit High Input

NOTE: This diagnostic procedure is written for scan tool operation. Drain valve can be operated by performing compulsory valve operation if Subaru Select Monitor is being used. See COMPULSORY VALVE OPERATION CHECK MODE  under SELF-DIAGNOSTIC SYSTEM.
  1. Perform test procedure. See TESTING PROCEDURE . Turn ignition off. Connect 2-pin Green test connector located under left side of instrument panel (near center of instrument panel on Legacy and Outback). See Figure, Figure and Figure . Turn ignition on. Using a scan tool, activate drain valve. While operating drain valve, use a DVOM to measure voltage of Brown/Yellow wire by backprobing between 35-pin ECM electrical harness connector B134 terminal No. 10 and good chassis ground point. See Figure. If voltage switches between zero and 10 volts, go to next step. If voltage does not switch between zero and 10 volts, circuit has returned to normal. Check for intermittent conditions. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  2. Turn ignition on. Using a DVOM, measure voltage of Brown/Yellow wire by backprobing between 35-pin ECM electrical harness connector B134 terminal No. 10 and good chassis ground point. See Figure. If voltage is more than 10 volts, go to step  4. If voltage is not more than 10 volts, go to next step.
  3. Check for poor contact in 35-pin ECM electrical harness connector B134. Repair connector as required. If connector is okay, replace ECM. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  4. Turn ignition off. Disconnect 2-pin drain valve electrical harness connector. See Figure, Figure and Figure . Turn ignition on. Using a DVOM, measure voltage of Brown/Yellow wire by backprobing between 35-pin ECM electrical harness connector B134 terminal No. 10 and good chassis ground point. See Figure. If voltage is not more than 10 volts, go to next step. If voltage is more than 10 volts, locate and repair short to voltage in wiring between ECM and drain valve. After repair, replace ECM. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  5. Turn ignition off. With 2-pin drain valve electrical harness connector disconnected, use a DVOM to measure resistance across terminals of drain valve. If resistance is less than one ohm, replace drain valve and ECM. If resistance is not less than one ohm, go to next step. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
  6. Check for poor contact in 35-pin ECM electrical harness connector B134. Repair connector as required. If connector is okay, replace ECM. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
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