Ford Mustang P0442 Engine Code: Causes + How to Fix

One of the most common issues that happens with the Ford Mustang is the P0442 trouble code. This code appears when connecting the vehicle to an OBDII scanner and pertains to the emissions system. 

While it’s unlikely to cause a breakdown, it can be bothersome and may result in a failed emissions test for your Mustang. 

Ford Mustang P0442

The most common cause of P0442 is a missing or damaged fuel cap.

What Does the P0442 Code Mean?

P0442 Meaning Ford Mustang

P0442 is a universal OBD II diagnostic trouble code, applicable across vehicle manufacturers. It has a two-part definition.

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

Evaporative Emission Control System

The EVAP system captures all fuel vapor from your car’s fuel tank and sends them to the engine’s intake to be ignited in the normal combustion process.

Leak Detected (Small)

When the Ford Mustang’s computer detects that the EVAP system has a leak, it will throw the P0442 code.

Different code numbers represent the leak size. P0442 indicates your Mustang has a minor EVAP leak.

Ford Mustang P0442 Code Symptoms

There are rarely any symptoms related to the P0442 code. 

You may notice the vague smell of gas near the back of your vehicle, the check engine light will illuminate, and you may or may not have a “check fuel cap message”.  

In rare cases, your Mustang may have difficulty starting after fueling up, indicating the purge valve is stuck open. 

Ford Mustang P0442 Causes

Numerous factors can trigger the P0442 error code in the Ford Mustang. The most prevalent issue is undoubtedly the gas cap. 

Bad or Loose Gas Cap

A bad or loose gas cap will also trigger this trouble code. So if it’s the first time you have experienced this issue, you may want to tighten the fuel cap and see if the code clears itself.

Just be aware that the engine may take several cycles to clear the code.

Your Mustang may display a message indicating that you need to tighten the gas cap; even if it doesn’t, the fuel cap is the first thing you should check. 

Inspect the O ring underneath the fuel cap and verify that it is present and not dry-rotted.

Ensure you utilize an authentic Ford gas cap for replacements to maintain optimal functionality.

EVAP System Leak

P0442 causes Ford Mustang
Purge valves come in many shapes and sizes

P0442 doesn’t specify where the leak is coming from, only that there is a leak.  Unfortunately, when this code appears by itself, it doesn’t specify which part of the EVAP system the leak is coming from.

A professional shop can use a smoke machine to test precisely where your Mustang’s EVAP system is leaking from.

Purge Valve

The vapor canister purge valve is a common cause of the P0442 trouble code and the Ford Mustang. The purge valve lets fuel vapor out of the charcoal canister and into the intake manifold.

They are easy to replace. There are a few clips that you need to find and remove. Pull the harness plug, and that’s usually it.

Purge valves are really cheap too. Always verify the fit for the model year and engine combination in your car.

Vent Valve

The vent control valve regulates vapor flow from the fuel tank/charcoal canister.  It controls the pressure in the fuel tank and prevents any gases from escaping into the atmosphere. 

A vent control valve is relatively easy to replace if you have all the necessary tools. The part is readily available online or at your local auto parts store.  The most challenging part is getting under your Mustang to get to it.

EVAP Hoses

A hose carries fuel vapor from the gas tank to the gas tank vent valve, and another hose runs from the charcoal canister to the intake manifold (gatekept by the purge valve). These hoses are often prone to cracking, tearing, and splitting. Always inspect this hose before any other repairs are attempted.

Charcoal Canister

Your Mustang’s charcoal canister is responsible for storing fuel vapors released from the gas tank. It’s an essential part of the evaporative emission control (EVAP) system and helps to reduce emissions. 

The charcoal canister traps these vapors until they are burned in the engine, ensuring that no air pollutants escape into the atmosphere. 

A leak in the fuel vapor hose leading from the fuel tank to the intake will throw P0442 in your Mustang.

Fuel Tank Pressure Sensor (If Equipped)

If the fuel tank pressure sensor has gone bad, it can cause many problems, including the P0442 code.

Not all vehicle’s have a fuel tank pressure sensor. You’ll need to verify if your Mustang has one or not.

Related: P0446 Ford Mustang, P0455 Ford Mustang

Common Questions

How Do I Reset P0442?

There are two ways to reset P0442.  You can plug a scan tool into your Mustang and command it to clear the codes, or you can repair the EVAP leak.  

If you clear the code without fixing the cause, it will return. If you fix the leak without clearing the code, the check engine light may take a few drive cycles to turn off.

Can You Drive With a P0442 Code?

An EVAP leak will not affect how your Ford Mustang’s engine runs.  While we recommend fixing your car as soon as possible, P0442 is not a breakdown risk.

How Much Does it Cost to Fix a P0442 Code?

Fixing a P0442 error code on your own typically ranges from $20 to $100, covering the most prevalent issues that trigger this code.  

Use factory Ford replacement parts so you’re not back under your car in a few years.


If your Ford Mustang has the P0442 OBD II code, you should first check the fuel cap.  If it’s missing or broken, replace it.

If the fuel cap seems ok, you must check the EVAP system for a leak.