P0446 Code: Toyota Tacoma (2016-2023) - Causes, Symptoms & Fixes

No recalls found in NHTSA database

No NHTSA complaints found for this make/model/year/issue combination in the provided data.

Note on data limits: The guide below relies on general EVAP (evaporative emission) system knowledge and typical Toyota Tacoma behavior for P0446. The absence of NHTSA recalls or complaints in the data means this DTC is not shown as a documented Toyota-specific recall in the supplied dataset, but P0446 can still occur due to common EVAP issues. Always confirm with Toyota service literature or your dealer if you have a vehicle-specific warranty concern.

CODE MEANING AND SEVERITY

• Code: P0446
• Full definition: Evaporative Emission Control System Vent Valve/Control Circuit Malfunction (often described as a vent valve circuit fault). In Toyota terminology, the vent valve is part of the EVAP system that vents the charcoal canister to atmosphere or to the intake in purge cycles; an electrical fault in the vent valve circuit (or its wiring) triggers P0446.
• Severity and implications:
  • Emissions-related fault: MIL (Check Engine Light) illumination is common.
  • Drivability: Most Tacoma owners do not notice obvious drivability problems from P0446 alone; however, the vehicle may fail an emissions test depending on state requirements.
  • Repeatability: The fault can be intermittent or persistent, and can be influenced by fuel level, temperature, and fueling conditions.
• What it means for the EVAP system: The PCM cannot correctly control the vent valve circuit, which prevents proper venting of the EVAP canister and can lead to incorrect evaporative tests during self-checks.

COMMON CAUSES ON TOYOTA TACOMA

• Faulty EVAP vent valve (solenoid) or its wiring/connector
  • The vent valve is a common failure point on many vehicles, including Tacomas.
• Faulty EVAP purge valve (solenoid) or related circuitry
  • Although P0446 is vent-valve related, purge-valve issues can accompany EVAP faults and confuse the diagnostic picture.
• Wiring harness or connector problems
  • Corrosion, loose connections, damaged insulation, or bent pins at the vent or purge valve connectors.
• Vacuum hoses or EVAP lines leaks or cracks
  • Cracked hoses, brittle tubing, or disconnections around the canister, vent tube, or purge path.
• EVAP canister or canister venting components
  • Canister damage or blockage can contribute to abnormal venting behavior.
• Gas cap or fuel system seals
  • A loose, cracked, or defective gas cap can sometimes trigger EVAP-related codes, though P0446 is typically vent-valve circuit related.
• Tampering or aftermarket modifications
  • Aftermarket fuel system parts or non-OEM hoses/connectors can affect the EVAP circuitry.
• PCM or electrical ground issues (less common)
  • A faulty PCM ground or power supply to EVAP valves can mimic a vent circuit fault.

SYMPTOMS

• Check Engine Light (MIL) on with P0446 in the trouble code.
• Possible emissions test failure due to EVAP monitoring not completing.
• Occasional fuel odor if the EVAP system is not venting properly, though odor is not guaranteed.
• Generally no noticeable loss of engine power or rough idle (drivability often preserved), but some intermittent tests may show check engine light during certain conditions (fueling, temperature, etc.).
• In some cases, a P0446 may occur alongside other EVAP codes (P0440–P0445 family), so multiple DTCs can coexist.

DIAGNOSTIC STEPS

Note: Always prioritize safety. Begin with basic checks and progress to electrical/system tests.

• Step 0: Visual and basic checks

  • Inspect the gas cap: ensure it is the proper OEM cap, seals correctly, and is tightened to the spec (usually “finger-tight” plus a quarter turn). Replace if cracked or damaged.
  • Inspect visible EVAP hoses for cracks, splits, or disconnections, especially around the vent valve and canister lines.
  • Inspect electrical connectors to the EVAP vent valve and purge valve for corrosion, bent pins, or loose fit.

• Step 1: Confirm the code and live data

  • Use an OBD-II scanner to confirm P0446 and review freeze-frame data. Look for the vent valve activity, duty cycle, and any voltage readings on the vent valve circuit when the PCM commands the valve.

• Step 2: Inspect the EVAP vent valve and wiring

  • Locate the EVAP vent valve (the vent solenoid) and check for proper operation and electrical continuity.
  • Check the harness between the vent valve and the PCM for damaged insulation, corrosion, or loose connections.
  • With the vehicle off, you can gently probe the valve connector for a steady 12V supply when commanded on (your scanner will show commanded state). If wiring shows short to power or ground, that is a fault.

• Step 3: Test valve operation

  • Using a scan tool that can command the vent valve, observe whether the valve actuates (clicks and changes circuit resistance) when commanded.
  • If the vent valve does not respond to commands or you detect an abnormal resistance (check spec in a repair manual), replace the vent valve.

• Step 4: Inspect purge valve and EVAP system together

  • While focusing on P0446, also inspect the purge valve for proper operation; a stuck or intermittent purge valve can affect EVAP diagnostics and complicate the symptom picture.
  • Ensure there are no fuel leaks or abnormal pressure in the EVAP lines.

• Step 5: Perform a vacuum/pressure test and/or a smoke test

  • A smoke test is highly effective to locate leaks in EVAP hoses, canister, and fittings.
  • A vacuum test on the EVAP system can reveal leaks in hoses, canister, or the vent valve pathway.

• Step 6: Check for related codes and data

  • Look for P0440, P0441, P0442, P0443, P0455, P0456 as related EVAP codes. If other EVAP codes are present, follow their diagnostic paths in addition to P0446.

• Step 7: Clear codes and test drive

  • After performing repairs, clear the codes and take the Tacoma on a strategy test drive (e.g., mix of city/highway driving) to recheck for reoccurrence of P0446.

• Step 8: If the fault persists

  • Consider professional EVAP testing with a smoke machine and more advanced EVAP system diagnostics, as some fault modes can be intermittent or evade simple checks.

RELATED CODES

• P0440 Evaporative Emission System Malfunction
• P0441 Evaporative Emission System Incorrect Purge Flow
• P0442 Small Leak Detected (evaporative)
• P0443 Evaporative Emission Control System Purge Error
• P0455 Large leak detected
• P0456 Very small leak detected
  Note: These are part of the EVAP family; if multiple EVAP codes are present, diagnose the complete EVAP system rather than isolating P0446 alone.

REPAIR OPTIONS AND COSTS (2025 prices)

Prices are approximate and can vary by region, shop rate, and whether OEM or aftermarket parts are used.

• Gas cap replacement

  • Parts: $5–$25
  • Labor: $0–$20 (or instant DIY replacement)
  • Typical total: $5–$45
  • Notes: Often the quickest and cheapest fix; if the gas cap was the root cause, this resolves P0446 in many cases.

• EVAP vent valve replacement (Toyota vent valve)

  • Parts: $40–$120
  • Labor: $60–$140
  • Typical total: $100–$260
  • Notes: A common fix for P0446; also verify wiring and connectors.

• EVAP purge valve replacement (if confusion with vent valve)

  • Parts: $30–$100
  • Labor: $60–$140
  • Typical total: $90–$240
  • Notes: If both valves show intermittent symptoms, both may be considered; usually one valve replacement suffices if diagnosed.

• EVAP canister/lines/hoses replacement

  • Parts: $30–$200 (hoses), $150–$600 (canister, if needed)
  • Labor: $150–$450
  • Typical total: $180–$1000+
  • Notes: Canister failures are less common but can be expensive; smoke testing will reveal leaks.

• PCM/ECU replacement (rare)

  • Parts: $500–$1200 (or higher for dealership parts)
  • Labor: $150–$500
  • Typical total: $650–$1700+
  • Notes: Only consider if electrical fault is confirmed and cannot be resolved by EVAP component repair.

• Miscellaneous repair costs

  • Wiring harness repair, connector replacement, or sealing leaks: $50–$300 depending on extent.

DIY VS PROFESSIONAL

• DIY (do-it-yourself)

  • Best for: gas cap inspection/replacement, visual hose checks, connector reseating, basic valve testing with a scan tool, and performing a smoke test if you own a smoke machine or have access to one.
  • Pros: Lower cost, hands-on learning, faster turnaround for basic fixes.
  • Cons: EVAP systems require careful diagnosis; misdiagnosis can lead to ongoing codes. Smoke testing equipment may be required.

• Professional (mechanic or EVAP specialist)

  • Best for: intermittent faults, wiring harness issues, valve replacement with proper diagnostics, smoke testing, or when multiple EVAP codes are present.
  • Pros: Thorough diagnostics, proper fixtures, and warranty on parts/service.
  • Cons: Higher labor costs.

• Decision tips

  • Start with simple checks (gas cap, hoses, connectors) and swap in a known-good vent or purge valve if you have access to tested parts.
  • If you’re not comfortable with electrical diagnostics, or if multiple EVAP components might be at fault, use a professional.
  • A reputable shop with EVAP smoke testing capability is highly recommended for persistent P0446.

PREVENTION

• Keep the gas cap tight and in good condition; replace if cracked or difficult to seal.
• Use good-quality hoses and ensure there are no cracks or brittle sections in EVAP lines; avoid kinking hoses during maintenance.
• Avoid overfilling the fuel tank; stop at the first click or as recommended by the owner’s manual.
• During fueling, ensure the EVAP system is not disrupted by spills; quickly seal after fueling.
• Schedule periodic EVAP system checks during routine maintenance (especially if you see the MIL on; early diagnosis prevents emissions issues).
• If you modify the fuel system or exhaust, revert to OEM components to prevent adverse EVAP interactions.

Final notes

• The data provided shows no recalls or official complaints in the given NHTSA dataset for the 2016–2023 Toyota Tacoma related to P0446. That does not rule out P0446 as a plausible diagnostic issue on these model years; it simply means there are no dataset entries in this specific report. If your vehicle is under warranty or you suspect a common TSB/recall related to EVAP, consult Toyota Customer Service or a Toyota dealer for the latest official information.
• If you encounter P0446, start with the gas cap and visual inspection, then proceed to valve electrical tests and a smoke test as needed. Use a diagnostic approach that confirms or rules out vent valve circuit faults before replacing components, and document any patterns (e.g., only after fueling or at certain temperatures) to guide the repair.