What Does Code P0446 Mean?
- P0446 definition: Evaporative Emission Control System Vent Control Circuit Malfunction
- Issue Severity: LOW– Continued driving for a short period of time is okay.
- Repair Urgency: Get this code fixed withing the next month to prevent issues related to the emissions system including failed inspections.
- Diagnosis: It is important to complete the entire diagnostic process when diagnosing the P0446 code. This DTC can be triggered by just about anything in your vehicle’s EVAP system from a loose gas cap to a defective part
The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. The fuel vapors from the fuel tank are absorbed and stored by charcoal pellets in the charcoal canister. The vent control valve is controlled by the engine control module (ECM) and allows air to flow into the charcoal canister to purge the gas vapors into the engine air intake to be burned. The flow of the gas vapors from the charcoal canister to the engine air intake is controlled by a purge valve.
The vent control valve is normally opened when the engine is on, and the purge volume control valve is normally closed and is controlled by the ECM to open when it is ready to purge the stored fuel vapors from the charcoal canister. However, the ECM occasionally performs leak tests to ensure the evaporative emission control system is working properly when the vehicle is turned off. During the leak test, the ECM closes the vent control valve to create a sealed EVAP system. When P0446 is triggered, the ECM has detected a short in the circuitry to activate the vent control valve, or the EVAP system failed to maintain the proper pressure during the active EVAP leak test.
- Missing, defective, damaged, or loose gas cap (most common)
- Defective EVAP Canister Vent Control Valve
- Distorted, damaged or cracked Fuel Tank Filler Neck
- Torn or punctured Evaporative system hose(s)
- Defective Fuel Tank Sending Unit gasket or seal
- Split or damaged Carbon Canister
- Defective or damaged fuel tank
- Open or shorted electrical connections
- Check Engine Light is on
- A slight decrease in fuel economy
- Gasoline smell
- Commonly associated with error codes: P0440, P0441, P0442, P0443, P0449
How Do I Fix Code P0446?
With a P0446 code, the first step is to get it properly diagnosed to figure out what is causing the malfunction in the EVAP system. Using the live data function of the FIXD sensor and app allows you to read and analyze fuel trims to properly diagnose a P0172 code.
If your engine is running lean and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal-certified shop to pinpoint the problem and give an accurate estimate for repairs.
These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.
How Much Does It Cost to Fix Code P0446?
If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0172 code.
Possible Repair Costs for P0446
When it comes to making repairs associated with the P0446 code, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.
- Loose/damaged gas cap
- EVAP hoses
- Fuel tank
- Charcoal canister
- Faulty vent control valve
- Faulty purge control valve
DIY Steps to Diagnose Code P0446
If you’d like to try to fix code P0446 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Diagnosis can require some specialized equipment beyond what the FIXD Sensor can provide, but this is usually still a beginner-level diagnosis.
DIY difficulty level: Easy
This repair is simple enough for beginners to attempt.
Tools/parts needed (our top picks from Amazon):
- Digital multimeter
- EVAP smoke machine leak checker
- Fused jumper wires
- Vehicle specific service manual
STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.
Use FIXD to scan your vehicle to verify P0446 is the only code present. If other codes are present, they must be addressed first. If it is paired with P0441 and/or P0440, there is most likely a solenoid failure, leaking charcoal canister, or a more complex EVAP leak.
STEP 2: INSPECT GAS CAP.
Inspect your gas cap to see if it is loose or damaged. If your gas cap is loose, tighten it and clear the code. Inspect your gas cap for physical damage or deterioration. However, it should be noted that damage to the gas cap or deterioration of its components is not always noticeable. If your gas cap was not loose and you do not see any indications of failure, try replacing the gas cap anyway and clearing the codes. Gas caps are relatively inexpensive and are often the fix for code P0446.
STEP 3: PERFORM EVAP SYSTEM LEAK CHECK.
If the fuel cap didn’t fix it, perform an EVAP system leak check. To do this, pinch off the vent tube to the EVAP Vent Control Valve. Pressurize the EVAP system with an EVAP smoke machine leak checker. Check to see if you see any smoke leaking out from any hoses or seals. If there are any leaks, repair leaks and check to see if the concern is resolved.
STEP 4: CHECK EVAP VENT CONTROL VALVE.
If you find no leaks, check the EVAP vent control valve for proper operation. This valve can get sticky, have debris caught in it, or the internal solenoid can fail and not operate. To test: Remove the EVAP vent control valve from the vehicle. (Tech Tip- The EVAP vent control valve is usually located under the car in the rear of the vehicle by or attached to the charcoal canister.) Verify with no power or ground supplied that you can blow through the valve’s openings. (If you can’t blow through the openings, the valve is stuck closed and needs to be replaced.) Now, supply power and ground to the solenoid (reference the service manual for your vehicle to find out which pins to supply power and ground to) the valve should click and now you shouldn’t be able to blow through the openings. If you can blow through the valve when it is powered on, then the valve is faulty and needs to be replaced.
STEP 5: CONSULT A PROFESSIONAL.
If at this point the vehicle is still setting the same code, you may have an electrical problem and will need to bring it to a shop to have further diagnostic work performed.
Common P0446 diagnosis mistakes
It is important to complete the entire diagnostic process when diagnosing P0446. Don’t overlook a loose or faulty gas cap as this is the most common culprit that cause the check engine light to come on for this code.
Still Need Help Fixing Code P0446?
If you’ve followed the steps above and are still experiencing a lean engine condition and code P0446, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.
Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals