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P0448Evaporative Emission Control System Vent Control Circuit Shorted

The engine computer detects a short circuit in the EVAP vent control valve's wiring or solenoid, which can keep the vent sealed and cause fueling and pressure problems.

Definition

The PCM monitors the vent solenoid driver circuit for correct current whenever it commands the valve. P0448 sets when the circuit is shorted to ground or voltage, or the solenoid winding is internally shorted, drawing excessive current. Beyond the MIL, a short that holds the vent valve closed blocks the canister's fresh-air path: the tank can pull vacuum, causing slow refueling with pump-handle click-off, a whoosh when removing the gas cap, groaning fuel-pump noise, and even fuel starvation on some vehicles.

Common causes

  • Internally shorted vent solenoid winding
  • Control wire chafed to ground along the frame rail or fuel tank straps
  • Water intrusion and corrosion inside the vent valve connector bridging terminals
  • Harness section shorted to voltage after collision or trailer-wiring repairs
  • Vent solenoid contaminated and seized, overloading the circuit
  • Faulty PCM driver (rare, often secondary damage)

Common misdiagnoses

  • Fuel pump replaced for refueling or starvation symptoms caused by a sealed vent
  • Gas cap replaced for a circuit-side fault
  • Charcoal canister replaced when the solenoid or wiring is shorted
  • Fuel tank or filler neck replaced for slow-fill complaints

Troubleshooting steps

  1. 1.Measure the vent solenoid coil resistance

    Compare to spec (commonly 20-60 ohms); a very low reading indicates a shorted coil requiring valve replacement.

  2. 2.Test the control circuit for shorts

    With valve and PCM disconnected, verify OL between the control wire and both chassis ground and battery positive.

  3. 3.Inspect the rear harness and connector

    Look for chafe points at tank straps and corrosion in the connector; the vent valve lives in the splash zone and water intrusion is common.

  4. 4.Confirm the vent valve opens when de-energized

    Unplugged, the valve should be open; blow through it or verify with a hand vacuum pump that air passes freely.

  5. 5.Check for tank vacuum symptoms

    A hiss or whoosh when removing the fuel cap after a drive confirms the vent path has been blocked.

  6. 6.Repair the fault, clear codes, and retest

    Cycle the vent solenoid with a scan tool and run the EVAP monitor to confirm normal sealing and venting.

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