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Smoke test requirements

My Hyundai Elantra is throwing a P0456 code for small eval leak. I was told that a smoke test was necessary after replacing the gas cap didn’t keep the CEL off. Can a smoke test be done if there’s more than half a tank of gas in the fuel tank? I’m being told no. Any thoughts? Can’t the dealer empty the tank enough to get the results necessary?

What’s the model year?

What’s happening I expect is the computer is completely closing off the evap system then as the car runs it causes a vacuum to form, the level of which is monitored by a pressure sensor. The code is saying the vacuum is not holding as well as it should over time; i.e. something is leaking. There’s more places a leak can form than I’m willing to type, but a common leak is the purge valve. A dealership shop might not use a smoke test for this, they might just test each leak-able device on and off one by one. They’d have a scan tool that can turn each on and off by command, so they’d check for leaks for each device that way.

It’s a 2015

1.8 L? 2.0 L? Is this an Elantra GT?

No it’s an SE

I believe it’s a 1.8

Besides the fuel cap the likely possibilities are: PCSV to Intake manifold Line , Canister Close Valve(CCV) Line, Fuel Tank Pressure Sensor, PCSV to Canister Line, Fuel Tank Lines .

Hyundai should have a test gadget (called a GDS) that will run an evap leak test automatically to facilitate a diagnosis. I’m not seeing anything specifically calling out a smoke test for this problem, so can’t be of much help on your original question. It’s sort of like if your swimming pool is leaking, you basically have to check each thing that could leak one by one. Like I suggest above, I’d start w/the purge valve.

I’m hoping whatever it is won’t cost me thousands and that it’s an easy repair. Haven’t been able to get the car inspected because of this.

This isn’t usually a big expense to fix. But the diagnosis can run into some labor time. Note that there’s a possibility there’s actually nothing leaking and the problem is the pressure sensor is inaccurate.

Thanks for your help. I guess we’ll see since they’ll have the car all day tomorrow. I’ll post an update once I know more

So I think I lucked out today. The problem was a bad evap canister. It was covered under warranty so no charge

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That said . . . I hope the dealer/shop did indeed verify the repair

In other words, I hope after the guy replaced the canister and cleared the code, he drove the car under the appropriate conditions, so that the evap readiness monitor ran to completion

It’s sad to say this . . . a lot of mechanics don’t understand the concept of “verify the repair”