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P0468EVAP Purge Flow Sensor Circuit High

The EVAP purge flow sensor signal is stuck above its normal operating range, usually from an open circuit, a short to voltage, or a failed sensor.

Definition

The PCM sets P0468 when the purge flow sensor's signal voltage exceeds the maximum plausible threshold — commonly an open signal or ground wire (letting the input float to the bias voltage), a short to a voltage source, or a failed sensor pegged high. The PCM cannot confirm actual purge flow, so it illuminates the MIL and suspends the EVAP purge monitor. There are typically no driveability symptoms, but the vehicle will fail a monitor-readiness emissions inspection until the circuit is repaired.

Common causes

  • Open signal or sensor-ground wire letting the input float high
  • Failed purge flow sensor with output pegged at reference voltage
  • Signal wire shorted to a 5 V or battery voltage source
  • Corroded or backed-out connector terminals creating an open circuit
  • Connector damage from previous EVAP service near the canister or intake
  • Faulty PCM input circuit (rare)

Common misdiagnoses

  • Purge valve replaced for a sensor circuit-high fault
  • EVAP smoke tests and leak repairs performed for an electrical code
  • Sensor replaced repeatedly when the harness has an open or short to voltage
  • PCM replaced before basic circuit testing

Troubleshooting steps

  1. 1.Measure the signal voltage at the sensor connector

    Key on, a signal pinned at about 5 V (or battery voltage) confirms a circuit-high condition; note whether it matches reference or system voltage to identify the short source.

  2. 2.Check the sensor ground circuit

    Measure voltage drop from the sensor ground pin to battery negative; anything over about 0.1 V indicates a poor or open ground that raises the signal.

  3. 3.Jumper the signal to ground briefly and watch the PID

    If grounding the signal at the connector drives the PID low, the wiring and PCM input are good and the sensor is at fault.

  4. 4.Inspect the connector and harness

    Look for backed-out terminals, corrosion, and chafe points where the harness routes near the intake or canister.

  5. 5.Test for a short to voltage

    With the sensor unplugged and key on, the signal wire should not carry battery voltage; if it does, find where it contacts a feed circuit.

  6. 6.Repair, clear, and verify

    Confirm the flow signal reads its zero-flow baseline key-on and tracks commanded purge at idle, then verify the code stays clear.

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