What Does the OBD-II Engine Code P0442 Mean?

The P0442 engine code means you have a problem with the evaporative emission control system. Here's how to diagnose and fix trouble code P0442.
Written by Tiffany Leung
Reviewed by Melanie Reiff
If you see engine code P0442, you have a problem with the evaporative emission control system. 
  • The P0442 code is not critical but it can damage your engine—so fix it ASAP.
  • Diagnostic trouble codes (DTCs) tell you what issues your car’s engine is having.
  • A scan tool like an OBD-II code reader can help you get an idea of the scope. 

What does the engine code P0442 mean?

Definition: Evaporative emission control system leak detected—small leak
The P0442 engine code indicates a problem with your car’s evaporative emission control system, which is responsible for preventing fuel vapors from escaping. 
These vapors are usually collected in a charcoal canister and burnt off by the engine.

How much will it cost to fix engine code P0442?

Cost of labor: Between $75 and $150 for one hour of labor diagnosing the P0442
Cost of parts: This varies depending on what part(s) you need to replace. On the low end, a replacement gas cap will cost $20-$40. On the high end, you may need to
replace the charcoal canister
for $200-$500.

What can cause the P0442 engine code?

The P0442 code indicates that the control module has detected a small leak in the Evaporative Emissions System (EVAP). The most common cause for this leak is a loose
fuel tank filler cap
The EVAP is responsible for keeping gasoline vapors contained so that they can be absorbed by the charcoal canister. When the car is turned off, the engine control module (ECM) carries out a leak test to ensure the EVAP system is working properly.
Other potential issues that could cause this engine code include
  • Missing or loose fuel cap 
  • Incorrect fuel filler cap in place 
  • Fuel filler cap will not close 
  • Something stuck in the fuel filler cap 
  • EVAP canister or fuel tank leaks 
  • EVAP system hose leaks 
  • Fuel tank leaks

Common symptoms of the P0442 engine code

You likely won’t notice anything when your EVAP system isn’t working aside from the check engine light turning on. Other potential signs to watch for include: 
  • Reduced fuel efficiency
  • Increased emissions
  • Gasoline smell

How serious is the P0442 engine code? 

The P0442 engine code is a minor automotive problem and will not affect your car’s performance or drivability. However, it should be resolved before your next emissions test or you could risk
failing the emissions inspection

You might be able to fix the P0442 engine code yourself

In some cases, you can DIY fix the P0442 engine code at home, but you should only carry out repairs if you can diagnose the fuel system issue correctly. 
Depending on the issue, you may have to do the following:
If you’re not sure what repairs your car needs, you can cause serious damage to the engine. Bring your car to a professional to complete a thorough diagnostic inspection and
car repairs
to stay on the safe side. Ask for a smoke test with a smoke machine.

How to repair the P0442 code

If you do decide to repair the P0442 code by yourself, identify what is causing the code to show up. 
Do a visual inspection of the fuel system, including control valve, EVAP hose, EVAP lines, and fuel tank pressure sensor. You’re looking for an EVAP system leak or other problem that would trigger an EVAP code.
Then, follow these steps:
  • Replace the gas cap.
  • Inspect the gas cap condition.
  • Clean the gas tank and gas cap with WD-40 cleaner.
  • Replace the gas cap with the correct model if it is damaged.
  • Replace the canister purge valve.
  • Inspect the canister purge valve next to the throttle body while the engine is running.
  • Check the vacuum port for its functionality with your finger—the purge valve is stuck if you experience sucking.
  • Replace the canister purge valve by removing the used purge valve and reinstalling a new one.
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