P0499 — EVAP System Vent Valve Control Circuit High

P0499: EVAP System Vent Valve Control Circuit High — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

EVAP System Vent Valve Control Circuit High. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • The malfunction indicator may illuminate; the fault does not necessarily produce an obvious driving symptom.
  • The malfunction lamp may be the only sign; normal driving does not exclude the electrical fault.

Possible causes

  • Shorted wiring, dirty or loose terminals in the vent-valve control circuit.
  • A defective vent-valve electrical actuator; module faults require further proof.
  • A wiring or connector defect should be excluded before a costly component replacement.

What to check

  • Read P0499 and related faults; retain freeze-frame information.
  • Inspect the vent valve and harness for moisture, rubbed insulation and connector damage.
  • Measure the circuit against the maker's specification; high electrical input alone does not prove excessive EVAP pressure.
  • Correct only the confirmed defect, then verify the result under the maker's specified conditions.

Also written as: P0499-00, P049900, PO499 (some scan tools add the fault-type byte, e.g. -00).