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sprinkles08, ASE Certified Technician
Category: GMC
Satisfied Customers: 23111
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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I have a 2007 gmc sierra, 6.6 duramax LBZ, one day got low

Customer Question

I have a 2007 gmc sierra, 6.6 duramax LBZ, one day got low oil pressure warning light and the chimes while slowing down for red light. No noise, engine sounded fine. Checked the oil, it was ok. I changed oil and filter. Still got warning. I then changed the oil pressure sensor from the dealer. No luck, replaced oil level sensor, again, no luck. had friend put on his machine. Number 5 cylinder over fueling, redid the injector seals (maybe fuel in oil. no luck, did oil pressure test mechanical gauge. at idle 14 or 15 psi, at 1800 rpm 40 to 45. gonna replace cluster, but don't think that is it. The chime is not tied to cluster. HELP
JA: Have you checked the oil? How old is your oil pump?
Customer: 2007 gmc
JA: Are you fixing your Sierra yourself? What have you tried so far?
Customer: I listed what ive done
JA: Anything else you want the mechanic to know before I connect you?
Customer: nope
Submitted: 1 month ago.
Category: GMC
Expert:  sprinkles08 replied 1 month ago.

Hello and welcome to JustAnswer!

It sounds as if you do have an actual oil pressure issue, especially if it's only coming on when decelerating or at idle. The oil light will come on if pressure drops below 13 PSI, if you measured 14-15 PSI sitting still then it's most likely dipping under that while driving and there is also gauge accuracy to consider.

When you tested pressure how long had the engine been running?

What gear was the transmission in?

Customer: replied 1 month ago.
engine was on ten min. was in drive and reverse
Expert:  sprinkles08 replied 1 month ago.

The oil wouldn't have been at operating temperature yet then so it will be even lower while driving and it's fully warmed up.

Customer: replied 1 month ago.
There are no symptoms other than the warning. Ill redo pressure test. when I did it previously the ten minutes, I was driving and holding test gauge out the window. 5 of the minutes was at 60mph. then city driving. that's the psi I listed. what would be next step? All the reading Ive done, many have said they never heard of oilpump going bad? A bearing prob? Im lost
Customer: replied 1 month ago.
one thing that is weird, when I check oil, dip stick oil pretty clear compared to pan oil. When I used to change oil, dip stick oil was black pretty quick.
Expert:  sprinkles08 replied 1 month ago.

The next step in diagnosing the low oil pressure would be engine disassembly to inspect the pickup, oil pump, crankshaft and bearings.