I bought this vehicle in September of 2020 from my local bergstrom dealership. It is a 2012 GMC Sierra 1500, with 148000 miles, 6 speed automatic transmission, 5.3 engine with active fuel management. Three months after I bought it the check engine light came on with code P0521. I brought it to my dealer since it was still under warranty and they replaced the oil pressure sensor and the screen with it. At this time they also told me that I had oil sludge, but as long as I did frequent oil changes it would go away. So for the last year I have been driving it and every time the engine light came on with the same code, My dealer would do an oil change. Four weeks ago the light came on and I could not get to my dealer so I did it myself with the oil recommended in my manual. The engine light went off. A week after that oil change I was doing 55 and my oil pressure started to drop from 40 all the way down to around 15, and the "Stop engine, oil pressure low" message came on with the oil light. I stopped the engine. I checked my oil and it was where it was supposed to be so being close to home, I drove it carefully home. I had it towed into the dealer the next day, And they told me that the technician did an oil change and noticed metal shavings on his glove. However, They did not save the oil, the oil filter, or the glove. And did not take any pictures of anything. They then recommended me an engine replacement. I said that they should cover the replacement and they told me they would call back with quotes. They never did. After being avoided and sent to voicemail I went in there and they told me that they did an oil change, And drove the truck for 45 minutes and could not replicate my issue, and they now recommend that I drive the truck for 500 miles and come back for a check up. They also told me that my oil pan gasket, oil cooling lines, transmission cooling lines, and power steering lines are leaking, although I've never seen it leak anything, and it parks in a heated garage. When I asked them why my oil pressure was low they could not tell me. So my question is, What would cause the oil pressure to drop while driving like that? Since my dealer cannot seem to tell me. I have also scheduled the 500 mile checkup as I am nearing that milage. Thank you in advance
I recommend using an independent honest mechanic. The dealership is only going to try and cover up GM's screwups (such as collapsing AFM lifters) and charge you for things that you don't need.
It could be several problems, bad oil pump, clogged intake screen, collapsed lifter like @mmj said and others. Why do you keep going back to the dealership that is doing nothing but ripping you off? Go somewhere else and if it's under some kind of used car warranty, send them the bill.
