How long have you had the car and if you bought it new or relatively new, have you seen a dramatic drop in fuel mileage? (I won't know liters unless you translate to mpg). Toyota is unique in that if the heater circuit fails or becomes lazy, the engine compensates for that air/fuel sensing by increased fuel dumping into the system. No codes will be thrown. You will need to get a computer that can graph live data and look at the wave. You are resting the black wires on the heater circuit. While the car is running and at temp. You can raise rpms to make a more dramatic graph. If it's jagged, even a second off in the lines, it means the computer is adjusting more fuel into it. In several years your cat will go bad. We are a Toyo fam and had a Honda before that. All older cars. Cat on the Honda went bad 150k? as well as both Toyotas around the same time. The Lexus is a little more in mileage and last emissions didn't look too good with hydrocarbons. And the current Rav is getting 15mpg and city driving is minimal. It's supposed to get 22-24. Even on a V6. You can try cheap Chinese ones off eBay if you are a home DIY person just to check and then use Denso after verification without a scantool, but use lots of penetrant as a lot of people say they mess up the threads on the bunghole if they don't take the time to unscrew penetrant and rescrew.. but the back probing of the two air fuels precat will show you. Look at the YouTube video by South Main Auto to see. If you're getting the correct mileage or close, keep them in. But the addage about if it ain't broke only applies of you understand broke can mean not as efficient. Because to throw a MIL, you need a below efficiency threshold cross. If you're above that very conservative number, no codes. The car's these days if you throw the code the car can go into reduced limp mode. I had a tire that went out of round in it's old age and started hopping and it threw the traction and VSC and check engine light and would stumble. Took it off the highway and looked for a place to dump it safely for the day and come back. After a restart, it cleared but I drove under 55 the rest of the way to not trigger that again. Sudden loss of power on a high speed freeway is not fun.