Had the same problem, both valve caps were missing from the passenger side. Possibly stolen from the parking lot while shopping or dining.....who knows. The other day my TPS went off, attributed the warning light to come on due to a sudden dip in temperature. Took the car from the garage and parked in a sunny section of my driveway. Checked a couple of hours later the light did not come back on. Put car back into the garage and checked the next morning....light is back on. checked tire pressure with a digital gauge and tire pressure was correct, front and rear. This is when I discovered 2 valve caps missing, took the car to the dealer and had new caps installed. I say installed because they had to calibrated, all in all it cost $8.43 for the valve caps and no charge for calibration or labor.