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.
Evaporative Emissions System Small Leak Detected
A vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) will store a P0456 trouble code after it detects two failures in a row during vehicle off-testing (an automatic check it runs every time you turn your vehicle off). There is not any accompanying symptom or OBD II trouble code other than a generic P0440 indicating a general problem with the evaporative emission fuel system. Your Check Engine Light will come on to indicate both codes, but there won’t be any other indication of a problem that affects normal operation or drivability.
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.
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.
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.
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.
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.