The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen).
There is no other way to say it: Legoland is the worst value for money of any theme park bar none. It's hard to know where to start: the Â£132 admission fee for a family of four, the Â£15 per person for the queue jumping system (that's free at all Disney parks), or the cynical Â£2 charge to leave the car park!
However, if you wait until the day or two beforehand, you will pay $83 per adult (same as the walk-up admission price) and $73 per child. Kids under 3 are free at Legoland, though you will have to buy them a separate ticket for entrance to the water park. If you suspect one day at Legoland is not enough, it is inexpensive to add more days, but make those purchases up front as well. You can also check the website of the nearby Costco on Palomar Airport Road as it sometimes sells discounted tickets. And AAA members can get reduced tickets.