P0446 — Evaporative Emission System Vent Control Circuit
P0446 sets when the ECM detects an abnormal condition in the EVAP vent control circuit or the vent valve does not operate as commanded. A clogged vent filter or hose is a very common cause — clean the area and inspect the filter before replacing the valve. Command the vent valve with a scan tool and listen or feel for operation.
Fault Overview
Failed vent valve (stuck open or closed), open or shorted control circuit, clogged vent filter or hose, connector issues, and PCM driver fault (rare) are the primary causes. Some vehicles locate the vent valve near the canister in a dirty environment.
Engine & Platform Coverage
Symptoms
- •P0446
- •EVAP vent control
- •vent valve circuit
- •P0446 canister vent
- •EVAP vent solenoid
Possible Causes
- 1.Failed vent valve (stuck open or closed)
- 2.Open or shorted control circuit
- 3.Clogged vent filter or hose
- 4.Connector issues
- 5.PCM driver fault (rare)
Wiring & Circuit Notes
Vent-valve connector and control wire. Check for corrosion, damage near the fuel tank, and proper ground.
DVOM Specs & Sensor Tests
Vent-valve resistance. Voltage on the control circuit when commanded. Ability of the valve to hold or release vacuum/smoke.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Command the Vent Valve Open and Closed: Command the vent valve open and closed with a scan tool. Listen and feel for operation.
- 2Step 2 — Measure Valve Resistance and Control Circuit Voltage: Measure vent valve resistance and control circuit voltage when commanded.
- 3Step 3 — Inspect and Clean the Vent Filter and Hose: Inspect and clean the vent filter and hose. A clogged vent path is a very common cause.
- 4Step 4 — Smoke-Test the System: Smoke-test the EVAP system with the valve commanded both open and closed to verify sealing and flow.
- 5Step 5 — Replace the Valve if It Fails to Operate or Seal: Replace the vent valve if it fails to operate or seal properly after cleaning and circuit verification.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Clean vent filter/hose $20–80; replace vent valve $80–350; repair wiring $50–200.
Related Codes & Pages
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.