Oil pressure gauge reads zero after 20 minutes on 2003 Chevrolet Suburban 1500

2003 suburban. Oil pressure guage reads about 40 at first, but after driving about 20 minutes, reads zero. Car runs fine.

Could this be sending unit?

How to test the guage?

Asked by for the 2003 Chevrolet Suburban 1500
do a manual oil pressure test to determine issue
3 more answers
do a manual oil pressure test to determine issue
sounds like oil pressure sensor is bad to check the oil pressure remove sensor and screw in oil pressure gauge if the engine isnt making a noise with oil pressure reading 0 then it is your sensor that is bad
Is the engine making any ticking or tapping noises? If not, then it is your sensor or guage. Screw in a manual guage in place of the oil pressure switch and get a reading. If there si no noise, chances are it'll read normal. To test the guage you need a variable resistor box (guage tester). Easier to just replace the sending unit and see what happens first.