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P0440 Error Code: Symptoms, Causes, Diagnosis, Fixes and Cost

  • Engine Codes
  • Natasha Young
  • 7 minutes

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Trouble codes are how OBDII informs us that your car needs your attention. Knowing these will come in handy if you want to be a better driver. But there are too many codes to start from. And hey, better now than never! How about the P0440 error code?  

P0440 error code

What is code P0440? 

The P0440 code means that the EVAP emissions system has a leak or is not working right. Rather of releasing gasoline vapors into the atmosphere, the EVAP system draws them from the gas tank and burns them in the engine. If there is a leak or a blockage in the pipes connecting the gas tank to the engine, the P0440 error code gets activated. 

Fuel vapors can’t get into the air because of the evaporative emission control (EVAP) system. When the vent control valve is open, fuel vapors from the fuel tank get to the charcoal canister via a vent line. The charcoal pellets in the charcoal canister soak up the fuel vapors and store them. The purge volume control valve controls the amount of fuel vapor that gets into the engine.  

When it is opened (it is typically closed), the engine’s vacuum draws the fuel vapors from the charcoal canister and into the engine’s intake manifold. Where they are used as part of the air-fuel mixture required for combustion in the engine’s cylinders. Since the 1990s, fuel tanks have been sealed this way to cut down on the amount of fuel that evaporates into the air. 

When code P0440 is set, the Engine Control Module (ECM) has found a leak or a vapor pressure sensor has failed. ECM knows when the car goes off. At this point, the ECM checks the pressure in the EVAP system, and if it doesn’t stay steady, it turns on the Check Engine Light. 

Most of the time, P0440 is paired with another code. The code that goes with it tells you more about where the problem is. P0440 is often paired with the following codes: 

  • P0441  
  • P0442
  • P0443  
  • P0447  
  • P0449  
  • P0453  
  • P0456 and other codes from the P044x series 

What are the causes of error code P0440? 

The following can possibly cause code P0440. 

  • Missing, broken, or the wrong-sized fuel cap. 
  • Damaged fuel tank filler neck 
  • Disconnected or damaged hoses in the EVAP system. 
  • Malfunctioning gaskets or seals on the fuel tank.   
  • Broken or leaking carbon canister.  
  • Faulty EVAP vent valve and/or EVAP purge valve.   
  • Broken or cracked fuel tank. 
  • Faulty fuel tank pressure sensor. 
  • Broken LDP pump or switch. 

What are the symptoms of error code P0440? 

The Check Engine Light will come on, and the code will be stored in the ECM. If the vapor leak is big enough, you may smell fuel vapor inside or near the car. 

How serious is P0440? 

The P0440 code is not an emergency code because it doesn’t affect how safely you can drive the car. But it could make your gas mileage go down. If you have the P0440 code and are about to take a new emissions test, you will fail.  

But it can get dangerous at times. The vapors can also catch fire and are dangerous to breathe. Even though the amount of gas released is small, it builds up over time. So, better get it diagnosed.  

How to diagnose error code P0440 

A loose gas cap, a broken hose, or a leaking fuel tank, among other things, could cause engine code P0440. You could follow the steps below if you want to try to fix code P0440 at home.  

Equipment needed: 

  • Simple hand tools 
  • Vacuum gauge (optional) 
  • EVAP smoke machine leak checker 
  • Jumper wires with fuses 
  • Vehicle-specific service manual 

Sometimes the P0440 code is easy to figure out if you know where to start. Here are a few things a professional mechanic would do to figure out what the P0440 code means. 

  • Hook up a Diagnostic Scanner and look for any error codes that might be related. Make sure the trouble code doesn’t get saved accidentally when filling up the tank. 
  • Ensure the gas cap is tight and the O-ring is in good shape. 
  • Check the solenoid for the EVAP purge. Make sure the line is sealed when closed, and test it with 12 volts and ground to ensure it works. 
  • Check to see if the EVAP purge solenoid is getting a signal from the ECU.  
  • Increase the pressure in the fuel tank pipe. If you think there’s a leak, use an EVAP smoke machine to find the leak. 
  • Clear the fault codes and drive the car for a few days if the system is sealed and the purge control solenoid functions. 

What are the possible fixes for the P0440 code? 

To fix the P0440 code, you should first ensure the gas cap is tightened correctly and that the rubber O-ring around it seals well. In some situations, you may need to fix a leak in the EVAP system or figure out what’s wrong with the EVAP purge control valve and replace it. 

  • Fix the gas cap and get rid of the trouble codes. 
  • Change the O-ring on the gas cap. Change the EVAP purge control valve. 
  • EVAP purge control valve wiring needs to be fixed. 
  • Replace the fuel tank.
  • Replace Canister.
  • Replace damaged EVAP pipes/lines.

How much does it cost to repair P0440? 

P0440 can be caused by a loose gas cap, a broken hose, or a fuel tank that leaks. You can’t give an accurate estimate without first figuring out what’s wrong. If you get the error code P0440, one or more of the fixes below may be needed to fix the problem. For each possible repair, the estimated cost includes the cost of the parts and the cost of the work needed to repair. 

  • EVAP Line $20-$100 
  • Gas Cap $20-$60 
  • Purge Volume Control Valve $150-$200 
  • EVAP Vent Control Valve $150-$200  

Usually costs between $75 and $150, depending on the shop’s hourly rate. Many, if not most, shops will add a diagnosis fee to the cost of any repairs you need if you have them done by them.  

FAQs on P0440 error code 

I got a P0440 code. Can I still drive? 

Even though this error code might not mean that your car isn’t working properly, releasing toxic and flammable vapors inside and around the car can be very dangerous for the driver and passengers. You should have a mechanic fix the car before trying to drive it. 

How hard is it to check for a P0440 code? 

Fixing a P0440 error code may be as easy as making sure your car’s gas cap is tight or replacing it if it’s broken. Usually, leaking parts of the vapor system, like a vapor control valve or carbon canister, need to be fixed or replaced. If that’s not the case, call a mechanic immediately. 

Does P0440 go away on its own? 

No, the P0440 code won’t go away on its own, even if you replace the broken part. This is true for almost all engine error codes. Even if the check engine light goes out, the code will still be in the car’s memory, which could cause problems in the future. So, when the repair is done, connect the scan tool and clear all error codes. So, you’ll know right away if everything is fine or if there are other problems. 

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