P0442 Code – Evaporative System Malfunction, Gas Cap Leak
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P0442 OBDII Code – Evaporative System Malfunction, Gas Cap Leak

gas cap replacementThe P0442 error code indicates that a small leak in the evaporative emissions system has been detected.

Evaporative emissions are just what they sound like: emissions due to evaporation of engine fuel from liquid phase to gas phase.

This is primarily relevant for gasoline engines, as gasoline is highly volatile as a liquid and tends to want to return to the gaseous state.

Evaporative emissions systems are designed to catch and store gasoline that has evaporated from the fuel tank or lines, and then the fuel will be re-used once the vehicle is in operation.

These emissions are tested from a regulatory perspective by leaving automobiles in a container for a prescribed amount of time, and then measuring the hydrocarbons that have evaporated from the fuel system. If limits are exceeded, the manufacturer must show that the fault will be set.

P0442 Code Symptoms

As described in the previous paragraph, the test for evaporative emissions is to leave a car in a box and measure the hydrocarbons. This is to simulate a vehicle being parked in a garage overnight.

In some cases, the symptoms may not be noticeable, but in more extreme cases it is possible that a symptom could be a hydrocarbon or gasoline smell in the garage.

Since gasoline has a higher tendency to evaporate at warmer temperatures, it is likely that any symptoms would be more noticeable in warmer ambient conditions.

If you do smell hydrocarbons in your garage, be sure it is not another gasoline canister that is not sealed properly. A failure in the system can also lead to an increase in fuel consumption, however in most cases this will not be significant enough to be noticed.

Causes of the P0442 OBDII Trouble Code

locking gas capThe P0442 error code is generally caused by some type of leak in the evaporative emissions system. Some of the primary constituents of this system are the fuel cap, filler neck, evaporative system hose, carbon canister, evaporative vent valve, or evaporative purge valve.

Damage to any of these could lead to the evaporative emissions test failing and setting of the P0442 code. Other possible causes could also be related to fuel tank issues, although this is less common.

The most common cause of this failure and the first thing normally checked is the fuel cap. Inspect the o-ring for any tears and replace if any are noticed.

It is also possible that this failure is caused by the fuel cap not being tightened after the last fueling of the vehicle. If no tears were seen, I would recommend removing and re-tightening the fuel cap, ensuring that the correct number of clicks were heard according to the owner’s manual.

How to Clear OBDII Codes After Replacing Your Gas Cap

Depending on the manufacturer, this code may clear itself or it may require that the failure code be cleared first. The preferred way to clear the code is using a diagnostic tool, but a battery disconnect will also accomplish this.

This evaporative emissions check is only performed in specific conditions, so if the problem is still present, it may take 1 week or more to reappear.

If the failure code is still present, inspect all components of the evaporative system carefully for any small tears. Pay special attention to any components with o-rings, and ensure that no cuts are present.


The P0442 evaporative emissions failure code is a minor issue from a vehicle performance perspective, but it can certainly be tedious to get resolved and avoid the warnings from your vehicle.

In case of minor leaks with no symptoms, I would recommend being patient and trying to fix by testing the gas cap, however if a strong hydrocarbon odor is noticed, this should be addressed more quickly.

I would recommend visiting your mechanic if you are not comfortable with inspection of the evaporative emissions system.