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  • The P0442 code stands for “Evaporative Emission Control System Leak Detected (Small Leak).”
  • Common causes of the P0442 code include a malfunctioning fuel cap, a leak or damage in the EVAP system line, charcoal canister, or fuel tank, a malfunctioning vent valve or purge valve, a faulty FTP sensor, or a failed leak detection pump.
  • An illuminated Check Engine Light or increased vehicle emissions are common symptoms of the P0442 code.
  • Tightening or changing the fuel cap is the easiest potential fix for the P0442 code and should be tried before anything else.

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.

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.

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 are the Possible Causes of the P0442 Code?

The most common causes of P0442 code are the following:

  • Malfunctioning fuel cap
  • Leak or damage in the EVAP system line
  • Leak or damage in the charcoal canister
  • Leak or damage in the fuel tank
  • Malfunctioning vent valve (leaking internally)
  • Malfunctioning purge valve (leaking internally)
  • Faulty FTP sensor
  • Failed leak detection pump

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.

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

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.

See also  P0440 Code: Evaporative Emission Control System Malfunction – Large Leak

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

Shops typically use a special machine that pumps the EVAP system full of smoke, which helps tremendously, in finding EVAP system leaks, but P0442 codes can be extremely difficult to find, even for a well-equipped shop. If you have recently hit something in the road or if you’ve had animals chewing on hoses and lines you might be able to spot damage by just doing a visual inspection. Check for split or disconnected hoses and/or broken plastic parts.

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.

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.

An In-Depth Look at Evaporative Systems

Evaporative systems have been around since California began requiring EVAP systems on cars in 1970. The gas smell from your fuel tank – hydrocarbon vapors from evaporating gasoline – is captured and stored in a special canister filled with fibrous material. A small vapor line runs from the top of the fuel tank to the canister, which retains the hydrocarbon vapors until they are purged by engine vacuum through a special valve. The canister has an open vent that allows atmosphere to flow through the canister as engine vacuum is applied to the canister’s purge port. A person who “packs” gas into their tank can cause the canister to become saturated with fuel, causing drivability issues like odd stumbles when the canister begins to purge.

See also  Why Does My Car Smell Like Gas?

Early canister purge valves had a ported vacuum line that triggered the purge valve to open a path from the canister to engine vacuum. “Ported” vacuum is only delivered when the throttle is applied but never at idle.

From 1970 to the mid 1990s, EVAP systems remained almost unchanged other than some OEMs using electric purge valves rather than vacuum triggered ones. With OBD2 regulations that became mandatory on all cars and trucks by 1997, EVAP systems got an upgrade. Some EVAP systems measured EVAP system flow using a thermistor or some other method. Enhanced EVAP systems were designed to detect vapor leaks as small as 0.020 (twenty thousandths) inch. While the older EVAP purge valves never opened at idle, modern EVAP systems are just as likely to purge the canister idling as they are driving down the road.

Rather than the canister being vented at all times, the most commonly described type of EVAP system monitor has a normally open electrically operated vent valve that is energized by the ECM/PCM to close the canister vent while a very gentle vacuum is applied to the canister through the purge valve, which the ECM/PCM operates using a duty cycle.

Since the hoses and the fuel tank are isolated from atmosphere at this point along with the canister, this gentle leak test maneuver traps that very weak vacuum in the fuel tank and the vapor lines and the ECM/PCM measures the negative pressure via a three-wire tank pressure sensor while the vacuum is applied. The ECM/PCM then closes the purge valve, trapping the vacuum in the system and watching the pressure. If the pressure leaks up a certain amount within a specified time interval, a code is stored by the ECM/PCM. A P0442 basically means a small leak has been detected.

See also  P0455 Code: Evaporative Emission Control System Large Leak Detected

Other Notes About P0442

It’s important to note that not all vehicles include a P0442 in their code library – most new Toyotas don’t include a P0442.

It’s important to note that not all vehicles include a P0442 in their code library – most new Toyotas don’t include a P0442.

Richard McCuistian, ASE Certified Master Automobile Technician

Furthermore, EVAP systems operate in several different ways besides the method described above, but every EVAP leak test is obviously designed to find EVAP leaks. Some systems have special valve assemblies dedicated to vapor leak detection.

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

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: One of the more passive methods of determining EVAP leaks is Chrysler’s “Natural Vacuum Leak” (NVL) detection method. GM uses a similar strategy on some of their vehicles (like the 2012 Buick Regal) and GM refers to their version as the “Engine Off Natural Vacuum” (EONV) test.

These systems basically work as follows: During vehicle operation, exhaust system heat is transferred to the fuel tank by default. With the key OFF and the EVAP system sealed, a change in the fuel tank vapor temperature and pressure naturally occurs. This pressure change is monitored by the ECM using the fuel tank pressure sensor input to determine whether there is an EVAP leak.

We don’t have room here to discuss all the different ways OEMs use to detect small EVAP leaks, but you get the picture.

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About The Authors
Richard McCuistian, ASE Certified Master Automobile Technician
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

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The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Pedro Soles

P0442 My mechanic solved it by disassembling the gas tank, he changed a viton seal that is submerged in the tank. I ordered this stamp to be prepared according to the model.

John F

What sort of “stamp” did you order? And what is it’s purpose?

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