How to fix code p0456

Last Updated on November 22, 2021

It’s always a hassle finding out that your car has sprung a leak somewhere. Immediately, your stress levels go through the roof and dark scenarios come popping into your head. Thankfully, due to breakthroughs in car design, most modern cars can diagnose issues and report them through their onboard computer.

DTCs, or Diagnostic Trouble Codes, are the way the onboard computer diagnoses different issues. If the Check Engine symbol lights up and a code P0456 is displayed, chances are that your car has sprung a leak on the evaporative emissions system.

DTCs, and in this case code P0456, tend to be quite reliable for reporting issues, as the leak has to manifest at least twice in a row during the self-diagnostic for the computer to display a Check Engine light.

What Does Code P0456 Mean?

OBD-II Trouble Code P0456 Description

Evaporative Emissions System – Small Leak Detected

The Evaporative Emission Control System (EVAP) plays a crucial role in preventing fuel vapors from escaping the enclosure and reaching the atmosphere.

It is a complex network of valves and hoses transporting these vapors to a charcoal canister to collect them. Once collected in the charcoal canister, the vapors need to go back to the engine for burning.

The computer has to regularly check for leaks in the system to prevent a potential fire and explosion hazard. This means either pumping or vacuuming air from the system and measuring the elapsed time. If the system detects a discrepancy twice in a row, the ‘Check Engine’ light turns on and a code like P0456 displays.

The diagnostic trouble code definition for P0456 is “Evaporative Emission System – Small Leak”, which is similar to P0457. The alternative is code P0455, which indicates larger leaks in the system. P0442 indicates an EVAP leak of the “medium” variety.

See Also: P0449 (EVAP System Vent Valve/Solenoid Circuit)

Symptoms of Code P0456

It can be quite tricky to notice the symptoms of code P0456 and correctly identify the issue. This is mostly due to the closed nature of the EVAP system. However, some of the most common symptoms that accompany code P0456 are:

• The ‘Check Engine’ light is on. This one always occurs once the computer detects a leak on the EVAP system.
• The smell of gasoline. This one is a little less straightforward, as it’s not always easy to smell the gas from a minor leak. Still, if the issue has been around for a while or the leak is larger than usual, the smell will persist and become noticeable.
• Decrease in fuel efficiency. This one is the hardest to notice because most of the code P0456 leaks are so minor that they do not significantly affect fuel efficiency.

See Also: P0496 Code (EVAP Flow During a Non-Purge Condition)

Causes of Code P0456

Since the EVAP system is closed, most causes of code P0456 are either on the system components or connections between them. The majority of the system is on the bottom of the car, exposed to the elements and physical damage.

These are some of the most common causes of code P0456 we encountered in the past:

• Malfunctioning purge vent valve or gas cap: either of these might fail to seal properly due to it being loose or damaged.
• Disconnected or leaking EVAP hose
• Leaking fuel tank
• Damaged or malfunctioning canister valve
• Leaking charcoal canister

Is Code P0456 Serious?

Code P0456 is an issue of minor severity and should not drastically affect the performance of the car. The risk of catastrophic failure due to code P0456 is minimal.

However, it’s still important that you take the vehicle to a registered repair shop, so the issue can be taken care of. Failure to do so will likely show up on your next emission testing.

How to Fix

During the process of fixing Code P0456, the diagnostics play a crucial role. Code P0456 leaks are usually tiny and therefore much more difficult to diagnose. This will take up more time; it’s not uncommon for a car to spend a whole day in the shop to find and properly repair the leak.

The procedure is as follows:

1. Connect an automotive scanner or reader to the connection and take note of all freeze-frame data that could help determine the time the leak occurred.
2. A thorough inspection of the vapor purge valve system takes place, checking all the hoses and connectors, as well as the valve itself. Any damaged components will be replaced.
3. Check the purge valve for potential signs of blockage, such as dirt or debris.
4. Inspection of both fuel tank and charcoal canister for potential leaks
5. Check the operation of the purge valve and charcoal canister vent valve by testing them with a multimeter.
6. Use a smoke machine to locate the leak on the EVAP system, along with the test vapor.
7. After repairs and replacements, restart the system. Clear the codes from the system and prepare the car for a test drive to see if the code persists.

Cost to Fix P0456

The majority of the costs for the Code P0456 repairs stem from diagnostics. On average, a minor leak issue associated with Code P0456 will set you back between $200 and $300, with the majority of those funds going towards labor and diagnostics.

The replacement of any hoses and valves is often inexpensive. Leaks on the tanks might be more expensive, bringing the cost of repairs into the range of $500 to $600.

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

When you turn off your vehicle, the control module sends a command to the purge control valve (PCV), closing the system and activating the evaporative vacuum pump. This is supposed to create a tiny amount of specified vacuum before monitoring the system for leaks.

If the system detects a vacuum value outside manufacturer specifications, that means there is a small leak somewhere in the fuel system. The first time this happens, the system logs the failure, but it does not illuminate the check engine light.

After the second failed test, the ECM will store a P0456 code before turning on the check engine light. A tiny Evaporative Emissions System (EES) leak code can often indicate the fuel filler cap or the purge vent valve isn’t sealing.

Symptoms

Again, the evaporative emission system leak isn’t a problem you will notice on your daily commute or going to the grocery store. The only indication you will get is the Check Engine Light, the P0440 code and P0456 code on an OBD II scanner.

Diagnosis

Finding the source of a P0456 code isn’t as complex as some diagnostic procedures. That being said, to ensure you treat the root cause (i.e. not just the check engine light), you do need to follow a step-by-step process so you don’t miss anything. Here’s how our mechanics diagnose and repair a P0456 code:

• The technician scans codes and documents what they find. Then they check the freeze-frame data to verify the time of the system fault.
• Next, the technician conducts a physical inspection of the entire vapor purge valve system, including the PCV purge valve and vent valve hose connectors. They are looking for damaged or loose connections in the hose, connectors and wiring.
  
• After determining that everything is sealed property and that there is no damaged wiring or connectors, the technician checks the purge valve vent for blockage from dirt, debris or spider webs (yes, that’s actually been the cause of a PCV failure) that could prevent a total vapor seal in the PCV.
  
• The final step is to perform a smoke leakage test on the fuel vapor system to locate any small leak in the hoses or seals. This is done by connecting a smoke test kit to the test vapor port and watching for any smoke that might leak from the evaporative emission system. They also check the fuel cap for vent leakage, and to make sure gas cap seals tightly. Sometimes a P0456 code will come up if the filler fuel cap isn’t tightened properly or no longer seals, so it’s best to verify that’s not the cause after checking the rest of the EES for leaks.
  
• Lastly, if the ECM is still showing the P0456 OBD II trouble code, the technician will check the purge control valve to see if it will hold a vacuum when activated. If it can’t, it likely needs replacement.

Common mistakes

DIYers and even some experienced mechanics often skip checking for leaks, frayed wiring/broken connectors and the smoke test and opt to replace the PCV. It’s not a cheap part to replace, and depending on the vehicle it can be a labor intensive process, too. This makes fixing the problem all the more frustrating when the vehicle continues to code P0456 and you’ve just spent significant time and money to not fix the issue.

As with any automotive troubleshooting process, always check wiring and connectors, hoses and seals before you replace any major components. These connections are the most susceptible to wear, tear and the ravages of time. Always check them first, and you will save yourself a significant amount of headaches.

How serious is this?

All things considered, code p0456 isn’t a critically serious problem that affects the safety or even the fuel economy of your vehicle. Left unrepaired, however, it can become a much more serious problem that does affect drivability. It can even have a cascading effect that causes multiple failures in other systems of your engine, leading to stalling and frequent breakdowns. 

Additionally, your vehicle will not pass a standard state emissions test if the leak is not repaired. If you live in a locality that requires annual emissions testing to renew your registration, you will need to find and fix the problem before it will pass inspection.

What repairs can fix the code?

Here are the repairs to resolve a P0456 code.

• Tightening down the filler gas cap properly every time (replacing the gas cap if it no longer holds a seal).
• Repairing or replacing any damaged wiring, connectors or leaking hoses/seals in the EES.
• Repairing or replacing the leaking/clogged PCV.
• Replacing a leaking purge valve.

Related codes

P0440

Conclusion

The process for fixing this error code underscores the importance of sound diagnostics procedures and taking your vehicle into the shop as soon as you see your Check Engine Light come on.

Hopefully it’s nothing more than a loose gas filler cap, but if it isn’t, you are heading off more serious problems in the long term. Get your car in the shop so your mechanic can find and fix the problem right away.