Error P0456 - Only when it's cold
 

Hey everyone,

Excited to be here. I bought a used 2018 NX300 just over a week ago and everything's been working great, yet there're a few things I need to work on and Im' hoping you guys can help.

In the beginning I got two errors with the engine light on: P0455 and P0456.

I took the car to mechanics, and fixed P0455. A fuel pipe was disconnected that was weird. They just popped it back in and the error went away. I was concerned so we did an Evac (Evap?) test as well to make sure there's no leak in the system, and they confirmed there's no leaking in the pipes, whatsoever. (They did it thorugh some sort of smoke? They are toyota certified mechanics, so I guess they are reliable)

However, 2 days after I came from the mechanic, I got a P0456 error. I thought it could be the gas cap as one of the mechanics mentioned there? So I opened and tightened the cap and reset the error. It came back on in 48 hours when I started the car in a cold morning. I took the car to the mechanic and after scanning, they again said that it's the gas cap and adjusted it. Two days later, the error came back up. This time I was away from the mechanic so I reset it myself (have a scanner) and the error was gone. For 4 days there was no error and the days were hot until last night when the weather got super cold suddenly. In the morning the error came back again! and I'm concerned again...

I went ahead and checked the history of errors in the car, realized the previous owner had this error from the first week of owning the car. It kept coming back every few months.
I'm wondering now,
1. Anything I can do to make sure it's the gas cap? (I've bought a new one, but it's being delivered now. Until it arrives in around 10 days, I just have to wait)
2. Given the mechanics did an evac (evap?) test, should I still pressure them to re-check the pipes and everything or am I being over sensitive?
3. I come from a V6, 2015 Lexus IS. I read that the NX has a bit rougher idle, and that seems to be very true, but how much vibration is normal?... (I have no vibration while moving, even at a very low speed, also usually goes away when I put the car on "Hold" in a red light wait)
4. Could someone please tell me this isn't a big deal so I can sleep tight tonight? Anything common that I can look into myself?

Thanks for sharing what you know <3
Best,

Update: Last night I got full gas, and there was some petrol smell. It made sense in the beginning since we were at the gas station but when I came back home (around 4KM away), we could still smell the gas quite heavily. So got quite worried.
In the morning when I started the car, I was hoping for the "Leak" error to come up yet nothing. I did know that some tests like leaking require maximum of 85% fuel tank (and not all the way up), so thought probably that's why the error isn't coming up. The smell of gas was still quite strong.

Drove to the mechanics and they investigated the smell. It ended up disconnecting the fuel tank and figuring if that had a leak, and YES, it did! On the top of the tank, there was a circular lid that had gone loose. When the tank was full, though very slowly, the gas was leaking from the top. When it wasn't full, the air was going in. So you can imagine the errors....


https://cimg6.ibsrv.net/gimg/www.clu...b4bdf0ec0f.jpg


They tightened those screws and I drove home in a quite smoother ride! Now the idle isn't as rough as it used to be! The only problem is, during the process of disconnecting the tank, some good amount of gas spilled all over the tank and though they dried it up, it still smells like gas, making me doubt whether there's still some sort of leak somewhere or not. Today is quite windy so I'm hoping all the smell will be gone by the morning (It's 7pm here now). I'll be driving the car tomorrow a lot, hoping we'd get below 80% of the gas to be able to see if it returns any errors.

Hopefully all is well now... Fingers crossed...

Anyone has any idea how long the gas smell probably stays there?... (It's outside the car, not inside)

As long as there isn't a continued leak, shouldn't last more than a couple of days. Gasoline evaporates pretty well.

Thanks for your response! :) It got like I was shouting in a cave :))))

And yup! The error is gone eventhough the car did run the check and the gas level was around 75% :)
So all's good now :)

Most likely it was a defect since brand new, but previous owner never really pushed for a resolution from Lexus.

Vehicle must of been assembled on a Friday afternoon.

Oh man that is actually true! I went to the vehicle alert history through the navigation system. They had the check engine on and off at times, and at the same time with the engine light, another error was showing for me which was there for the previous owner as well: "ultrasonic detecting and ranging system....".

Anyway, it's all in the past now. If anything pop up again, I'll definitely post here!