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P0442 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


When diagnosing your check engine light, if your OBD2 scanner shows code P0442, then that means there is a small leak in the EVAP system.


All modern cars have an Evaporative Emissions Control System (EVAP). This system is designed to trap toxic vapors in the engine before they are released into the atmosphere. The vehicle’s internal computer and power control module (PCM) monitors the EVAP for any leaks. If there is a small leak, code P0442 will trigger the check engine light.


Although this code signifies a small leak, it can turn into a much bigger problem if left unchecked. The most likely reasons for P0442 are the following:

  • Faulty or Loose Fuel Cap – when refilling your car with gas, the fuel cap helps insulate the system so vapors can’t get out. If you didn’t seal the cap tightly, or the piece itself is faulty, then a leak can occur.
  • EVAP System Line Leak – as with other parts of your car’s engine, the EVAP system is highly complex. If there is a leak within one of the lines carrying vapors or fuel, it will trigger the code.
  • Charcoal Canister Leak – charcoal is excellent at absorbing toxins from the air, so this canister plays a vital role in trapping emissions. If it’s not sealed correctly, those vapors can get out.
  • Fuel Tank Leak – if you also notice that your gas gauge is dropping faster than usual in addition to P0442, it could mean that the fuel tank is leaking gas.
  • Failed Vent or Purge Valve – the EVAP system has a series of valves and vents to regulate emissions and take in the fresh air. These components can fail, causing a leak in the system.


In most cases, the only way you’ll know about a leak in your EVAP is when the check engine light comes on. Since this problem doesn’t cause substantial damage, you won’t likely notice any warning signs beyond the light.

That being said, if the cause is a leak in the fuel tank, that can cause your gas mileage to drop over time. Again, if your check engine light comes on and you notice your gauge dropping faster than normal, this is the probable cause.


There are several steps you need to take to identify the source of the leak. Since it can occur in any part of the EVAP system, you have to be thorough. Also, keep in mind that there may be more than one component that fails. For example, just because you tightened the gas cap doesn’t mean it couldn’t be an issue with the charcoal canister.

Follow these steps precisely to diagnose P0442 correctly.

  • Using your OBD2 scanner, look at the codes present. If there are multiple codes in the engine, write down any additional ones beyond P0442, as you’ll have to address them later.
  • Reset the codes, and then start driving the car. If the check engine light comes on again, look at the freeze frame data to see if the same codes reappear. If P0442 is still present, then you’ll have to perform an inspection.
  • Look at each piece of the EVAP system, checking for cracks or breaks in any component. Hoses, wires, and lines can all be damaged, so inspect each one carefully.
  • Look at the charcoal canister and check for cracks.
  • Use a scan tool to check the seal on the gas cap.
  • Use a scan tool to check the fuel tank pressure. If the pressure is lower than average, the tank likely has a leak.
  • EVAP systems have solenoids that help vent the vapors. Check to see if they are damaged or cracked. You’ll likely have to use a scan tool to verify that they are working properly.

Finally, you can conduct a smoke test to see how well the EVAP system is working. However, these testing machines can be expensive, so it’s usually best to have a professional do it. The liquids within the EVAP are flammable, so trying to create smoke with fire is highly dangerous.

Common mistakes

In most cases, the leak is caused by an unsealed gas cap. We recommend starting there after clearing the code to see if it will come on again. If it does, then you can check the rest of the EVAP system.

Also, don’t forget to check each component. Even if one is faulty, another piece could be too, so be thorough.

How serious is this?

As long as there isn’t a leak in the fuel tank, this code is not severe. However, if you ignore it, it will be impossible to tell if the check engine light is coming on for a different code. We always recommend clearing your lights so that you don’t miss another potential problem.

What repairs can fix the code?

Again, the most common cause is the gas cap. However, here are some other ways you can fix the code if that’s not the culprit.

  • Replace the fuel tank (if it’s leaking)
  • Replace the charcoal canister (if it’s broken or cracked)
  • Replace the EVAP lines (get a professional to do this for you)
  • Replace the purge or vent valves. You will need to make sure you get the right valves for your car, so take care to find the precise make and model.

Related codes

There can be other problems within the EVAP system, and codes related to that are P0440 through P0449.


While this code isn’t serious, it can prevent you from noticing other problems with your car. We highly recommend checking it out to ensure that your vehicle is working correctly. That being said, always start with the gas cap and then do more if that doesn’t solve the issue.

P0442 Code – What Does It Mean & How To Fix It