I have a 2002 STS with 55,000 miles. last week I got the low oil pressure warning chime three times while slowly turning through a parking lot at work (after driving 12 miles to get there). I only use Mobil 1 5W30 and the car has not been abused. The engine does not use any oil and it is always changed when the indicator gets to the 50% oil life. Are the sending units a problem here or am I looking at a big expense? I am going to try changing th sensor first.