tmlinfinit

Hi There,

I have a 2007 IS250 AWD and have been searching for threads similar to the issue I am experiencing but have had no luck so I'm hoping some of you could provide some insight.
The car has around 138,000km on it and I fill up using Octane 91 (Premium at Petro Canada only). I always stop the fill up when the gas pump handle clicks. I never over fill.

A month and a half ago, the Check Engine & VSC lights came on.
The dealer identified an exhaust leak around the Y-pipe area and recommended a shop to take my car to. The Y-pipe section was cut out and replaced and the Check Engine & VSC lights went off for a month and a half.

The lights appeared again last week.
I have noticed that the lights generally come on when the gas tank is just over 3/4 full but not full.

The lights then go off when the gas tank is around 1/2 full.

I was able to replicate this issue twice over the last week.

I took it to the dealer and they pulled up the codes and said they were seeing a code related to the CCO (catalytic converter).

But if it was a CCO issue, wouldn't the lights stay on regardless of the level of gas in the tank?

Additional observations include something peculiar with the gas cap.
When the engine / VSC lights are on, I tighten the gas cap (clockwise) until it clicks but after a few seconds, I hear a very tiny click where the gas cap turns ever so slightly (counter clockwise). Is this normal?

It doesn't happen when the tank is 1/2 full or less (which is when the engine / VSC lights are off).

The dealership says the codes don't pertain to a gas cap issue so now I'm left wondering what the real issue is.

After fixing the Y-pipe, I don't want to prematurely spend money on something that may not be the root cause. Changing the affected CCO (whichever one is affected) is fairly expensive as I have been told.

Really hoping some of you could provide some insight.

Thanks.