On my 04 lexus, the VSC, Trac off and engine lights are on. What do or can i check for to diagnose and fix?

You get a check engine light with other things, it accompanies a misfire, rich or lean mix, abs and brake lights, or gas cap leakage, (like you had to change pumps, when you started left the cap off, just going a few feet) you may get it, will go out by itself in a few miles(gives you a hint), bad timing changes the fuel mix, fuel pump rail pressure also, intermittent spark plug or lead firing, (produces a rich mixture), altitude compensator also, could produce rich or lean, so you want to know which codes you have for the proper diagnoses. what to bypass, where to look, which vac hoses to investigate, where to check rail pressure, a little experience once taught me that water in the fuel system will turn on all kinds of lights, (stop at an old station, fill up, water in his tanks, or other contaminates, try adding some heat to the next fueling) Heet forces fuel and water to mix, burns out the water, (another hint, indications are on the plug when misfiring, little tiny droplets or beads of water on and if the plug is pulled immediately when engine is run a very short period to less than operating temp! Also a pesky little critter is the tank crash shutoff valve, if it fails, lower G forces may turn it off, or stick it partially open. I have seen all these things discussed, and what i have mentioned fixes the car. (most times) sometimes changing the fuel filter will just do wonders, not expensive, $13,00 bucks plus labor of minimum charge per hr. usually a 30 min minimum charge, and usually the cheapest thing on the system to do!! Does this help?

I pulled the engine codes (P0136: P0137) and it sais to replace the O2 Sensor (bank 1 Sensor 2). It took care of the VSC, Trac Off and CEL lights. In addition is increased my gas mileage a little. I had also noticed the it was, intermitanlty, not shifting into Overdirve and it fixed this too. Be aware that Bank number for the 3MZ-FE can be difficult to pin down properly. Bank 1 is the firewall side and Bank 2 is the radiator side. Sensor 1 is upstream (Engine side) of the catalytic converter and S2 is the downstream (Muffler side) of the catalytic converter.