It's all at the Scion tC FAQ Site!
How do i clear the 'maintenance required'/oil change light using the trip meter button?
if at the time you changed your oil, you or the person changing your oil did not reset the 'maintanence reqiured'/oil change light or if you would just rather turn it off instead of setting the interval (aka- the lazy way to turn off that annoying light), follow these steps:
step 1 turn the key to the 'on' position.
step 2 reset both trip meters to zero. you can reset the trip meters to zero by selecting trip a or trip b and holding in the trip meter button for five (5) seconds.
step 3 after both trip meters are reset, select any trip meter and hold in the trip meter button and start the car.
step 4 continue holding the trip meter button until the "maintenance required' light disappears.
how do i reset and/or specify the interval for the 'maintenance required'/oil change light using the trip meter button?
the tC's ecu (computer) memorizes the distance your car has traveled. scion recommends that you change your oil every 5,000 miles. when your car exceeds 4,500 miles, the ecu will flash the maintenance required light for 12 seconds after turning the key to 'on'. if it exceeds 5,000 miles, then the ecu keeps the maintenance required light on until it is reset. so, how do you reset it? follow these steps (this procedure is also listed in the tC owner's manual, pg. 96):
step 1 turn the key to the 'on' position. using the trip meter button, toggle the lcd until 'ODO' is displayed.
step 2 turn the key off. now, push and hold the trip meter button. while holding the trip meter button, turn the key to 'on'.
step 3 while you continue to hold the trip meter button, you will see on the lcd disply five (5) small dashes and they will begin to 'count down' rather quickly.
step 4 continue holding the trip meter button and once all the dashes have been cleared, your lcd will display six zeros (000000) - release the trip meter button now - and then the lcd will display 'ODO' and your current mileage. at this time, your 'maintenance required'/oil change light has been reset.
*note* each dash represents 1,000 miles. if you like to change your oil every 3,000 miles for example, release the trip meter button when only two (2) dashes remain. that way, you will get the reminder light at the next 3,000 mile mark instead of 5,000.