The oil gauge on my dads 05 silverado reads high (around 80 psi) at all times. When the car is off it's obviously not working. But when he puts the key in the on position without the car running it shows at 80 psi and when he has it running it also shows at 80 psi. We figure it's either the sensor or maybe an electrical problem in the dash, but we'd like any help figuring out which one if anyone has had the same problem and feels like chiming in that would be great. Thanks.

2005 silverado 4wd 5.3L Auto