The sensors for the Tire pressure Monitor are mounted to the valve stems. You have to remove the tire from the rim to replace them. There is no circuit diagram. Before you go and have the sensors replaced, just try re-learning them. On your driver information center (the buttons that allow you to change the options and display the odometer, fuel usage and oil life, there is a setting that says "To relearn Tire Sensors, Press and hold (check mark key). When you do this, the horn will sound twice to let you know you are in learn mode (and the left front turn signal light will light up solid). Then, starting with the left front tire, let the air out slowly until the horn beeps once. The left front t-sig light will go out and the RF one will light. Do the same for the next 3 tires (the procedure is LF, RF, RR, LR). It will take about 8-10 lbs of air to do the learn, so make sure all the tires are full before you start. Once you do the last (LR) tire, the horn will beep twice again to let you know the procedure completed. Then set all the tires to specs and look at the info on the Driver Information Center (DIC) and see if they read right and the warning is gone. You may have to drive the vehicle around the block once at over 15-20 MPH to get the message to go away and reset. If it still has issues, then you will need to take it to a shop. Other than the re-learn procedure, the repairs will not be a DIY at home type thing (unless you just happen to have access to a tire mounting machine and wheel balancer!).