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DTC P0448: EVAP System Vent Control Circuit High Input

  1. Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE  . Turn ignition off. Connect test mode connector under left side of dash. See Figure . Turn ignition on. Using scan tool, activate drain valve. While activating drain valve, use DVOM connected to ground and backprobe ECM connector B137 (31-pin connector) terminal No. 11. See Figure . If voltage switches between zero and 10 volts while drain valve is being commanded on and off, go to next step. If voltage does not switch between zero and 10 volts while drain valve is being commanded on and off, circuit has returned to normal. Check for poor terminal contact in ECM connector.
  2. Turn ignition on. Using DVOM connected to ground, backprobe ECM connector B137 (31-pin connector) terminal No. 11. 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 terminal contact in ECM connector. Repair connector as required. If connector is okay, replace ECM.
  4. Turn ignition off. Disconnect electrical harness from drain valve. Turn ignition on. Using a DVOM connected to ground, backprobe ECM connector B137 (31-pin connector) terminal No. 11. If voltage is more than 10 volts, locate and repair short to voltage in wiring between ECM and drain valve. After repair, replace ECM. If voltage is not more than 10 volts, go to next step.
  5. Turn ignition off. Measure resistance across drain valve terminals. If drain valve resistance is less than one ohm, replace drain valve and ECM. If drain valve resistance is not less than one ohm, go to next step.
  6. Check for poor terminal contact in ECM connector. 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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