GMC Sierra P0446 Code Diagnosis- OBDII

P0446 GMC Sierra

This is one of the most commonly encountered trouble codes for the GMC Sierra Is the Code P0446. This trouble code is the number given when you connect your Sierra to an OBDII scaner. The trouble code P0446 indicates that the evaporative emissions control system is failing. This code is often found with P0441 or P0440.

P0446: Evaporative Emission Control System Vent Control Circuit Malfunction

Normally, P0446 does not pose a threat to vehicle driveability. Certainly anytime the service engine soon light is on, it’s good to deal with it as soon as possible though. This is usually accompanied by P0442. More information is available at GMC Sierra P0442 OBDII Cod. The common trouble code P0420 can be found alongside P0446.


Índice de Contenido
  1. GMC Sierra P0446 OBDII Code Symptoms
  2. GMC Sierra P0446 Meaning
  3. Sierra P0446 Trouble Code Causes
  4. P0446 Diagnostics- GMC Sierra
  5. Most common P0446 fixes

GMC Sierra P0446 OBDII Code Symptoms

GMC Sierra P0496 OBDII Code
Most often, P0446 will only be a check engine light.


Most commonly, the P0446 code does not cause any symptoms. Although the service engine light may come on soon, that's usually all. It is possible to notice an increase in fuel consumption, but it is unlikely. You may notice a gasy odor from P0446. It is related to fuel vapors.


GMC Sierra P0446 Meaning

The universal OBDII code P0446 can be used to diagnose trouble codes. It means that no matter what make or model vehicle you have, this code will still mean the exact same thing. Technically speaking, it stands for the following:

Evaporative Emission Control System Vent Control Circuit Malfunction

The EVAP captures any fuel vapor in the fuel tank. It then transmits these to the intake to allow for normal combustion. If the EVAP control circuit vent control circuit does not respond to the ECU it will throw the OBDII code P0446.

Sierra P0446 Trouble Code Causes

You can have the P0446 error code trigger in your GMC Sierra for many reasons. The most frequent problems that trigger this code are:


  • Vapor Canister Purge Valve– One of the most common causes of the P0446 code is the vapor canister purge valve.
  • It’s really easy to replace. You will need to locate and take out a few clips.
  • Hose for Evap System– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. The P0446 code will be generated. It should have a hole or tear.
  • A Faulty Canister of Charcoal– The charcoal canister is often the cause of P0446.
  • Fuel Tank Sending Unit– It is possible for the fuel tank sending unit to go bad. This could cause line pressure to drop and throw off the code.
  • Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. You may not get the message but a P0446. This will save you time and money.
  • Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. It is possible for this gasket to dry, particularly if vehicles spend a lot of time in dry environments. When it dries out, the fuel tank can’t hold pressure anymore.


P0446 Diagnostics- GMC Sierra

The mechanic will have a lot of different tools at his disposal in order to determine the cause of your GMC Sierra P0446. The most commonly used methods to diagnose this code are:

  • The mechanic will check to make sure there are no other codes. It is easier to diagnose problems if there are more codes. That’s because when they appear together in certain combinations, there will often only be only a few conditions that will throw any combination of codes at one time.
  • The mechanic will normally determine what trouble codes are associated with P0446. Take a look at the EVAP system. It includes the purge valve and line as well as the canister.
  • To ensure that the cap can withstand pressure, the mechanic will check it. If you are getting a warning that your gas cap is off, even when it’s on, replacing it will more than likely clear this code.
  • Monitoring and checking the fuel tank pressure is a must.
  • Following the inspections and repairs, the mechanic will conduct two more tests.
  • A smoke test, and they’ll use a scan tool to confirm that the EVAP solenoids and valves are operating properly.

Most common P0446 fixes

P0446 GMC Sierra Fix

These are some of the most popular Sierra P0446 fixes.

  • Replacing the gas cap
  • Replacing EVAP lines
  • Replace charcoal canister
  • Replacing the fuel tank

It is best to begin with the gas cap, and then work your way up to the fuel tanks. The gas cap is the most difficult and cost-effective item to replace.

Here’s a great video on How to test your gas tank.

You will need to find the cause of your GMC Sierra throwing the P0446 code. This should help. You can add any additional information by leaving a comment.

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