The yellow wrench flashing means that you are due for an oil change. Once the oil is changed, either the mechanic or you can do the following to reset and remove the yellow wrench.
1. Push in the odometer trip reset button while do step 2
2. Turn the ignition key to position #1 (meaning the first click) do not attempt to start the car.
3. After about five seconds the yellow wrench will stop flashing.
4. Return the key to off position and let go of the odometer trip reset button.
5. Turn on your car and the yellow wrench will go away.