OBD-II Trouble Codes

P0442 Code: Evaporative Emission Control System Leak Detected (Small Leak)

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The P0442 code is one of the many OBD-II codes that can trigger if your vehicle perceives an issue with its EVAP system.

In this article, we’ll explain what a P0442 means, what the possible causes and symptoms are, and how you can go about diagnosing and fixing the issue.

mechanic using an obd scanner to diagnose a car
A P0442 code indicates that there is a minor leak in your vehicle’s EVAP system.

What Does the P0442 Code Mean?

Diagnostic trouble code (DTC) P0442 stands for “Evaporative Emission Control System Leak Detected (Small Leak)”. Your car’s computer will set the code when it determines there’s a minor leak somewhere in the evaporative emission control (EVAP) system.

What is an EVAP System?

The EVAP system’s primary purpose is to block fuel vapors from escaping into the atmosphere. Although system designs vary, common primary components found within this system include the fuel tank, gas cap, purge valve, vent valve, and EVAP (charcoal) canister.

The system must be free of any leaks to comply with emissions regulations. To check for said leaks, the powertrain control module (PCM)—your car’s primary computer—will perform self-tests when certain criteria are met.

During a typical “small leak” test, the PCM first opens the purge valve to create a vacuum in the system. The device then seals the EVAP system by closing both the purge valve and the vent valve.

Finally, to check for leaks, the PCM monitors vacuum decay via a fuel tank pressure (FTP) sensor. If a small leak is detected, P0442 or another small leak code will be set.

Typically, the PCM will only set the code if it sees the system self-test fail twice.

The above description is how most systems operate. But of course, keep in mind that some vehicle makes use a slightly different method for identifying leaks.

For example, some applications may use a leak detection pump and switch.

What are the Possible Causes of the P0442 Code?

The most common causes of P0442 code are the following:

tightening a gas cap
Tightening the fuel cap is usually the first thing to do when fixing code P0442.

What are the Common Symptoms of the P0442 Code?

Typically, the most common symptoms you are most likely to experience if your vehicle is triggering the OBD-II trouble code P0442 would be an illuminated Check Engine Light or increased vehicle emissions.

In some cases, you may notice some pronounced fuel odors, although this is less common.

How to Diagnose the P0442 Code

When dealing with a P0442 code, the first thing a layperson should do is make sure the fuel cap is on tight, because if it’s loose, that could easily trigger the code.

If tightening the cap doesn’t work, you may want to try purchasing and installing a new cap.

Keep in mind: once you’ve tightened or replaced the gas cap, you’ll have to clear the code with a code reader or scan tool afterward. The code won’t immediately go away on its own.

Other than the gas cap, there are numerous potential causes that can trigger the OBD-II code P0442. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the videos below:

How to Fix the P0442 Code

There are multiple underlying causes that could trigger a code P0442. Therefore, there isn’t a “magic bullet” fix for the issue. You can try tightening or replacing the gas cap, as mentioned, or perhaps even do a visual inspection of the EVAP system components to check for any physical damage that could be causing a leak.

Other than that, you’ll need to diagnose the code accurately, as outlined above, to be able to perform the most appropriate repair for your specific case.

Also, keep in mind that all cars are different, so when troubleshooting and repairing diagnostic trouble codes, make sure to consult the factory repair information for your application.

Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.

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Staff Writers

In the Garage with CarParts.com is an online blog dedicated to bringing DIYers and devoted car enthusiasts up to date with topical automotive news and lifestyle content. Our writers live and breathe automotive, taking the guess work out of car repairs with how-to content that helps owners get back on the road and keep driving.

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