P0521 Buick Code - Engine Oil Pressure Sensor Performance

I COULD NOT FIND ANY ONLINE ARTICLE THAT COULD TELL ME WITH ABSOLUTE CERTAINTY THE CAUSE FOR CODE P0521 OR P0523 ON MY 2008 BUICK LACROOSE SUPER. BOTH CODES ARE ASSOCIATED WITH ONE ANOTHER AND HAVE TO DO WITH THE OIL PRESSURE. CAUSE VARIES AND COULD BE ANYTHING FROM NEEDING AN OIL CHANGE TO THE OIL PLUG FOR THE OIL PAN NOT BEING TIGHTENED PROPERLY. THEN THERE IS THE POSSIBILITY THAT THE OIL PRESSURE SWITCH NEEDED TO BE REPLACED. THIS SEEMED A LOGICAL FIX AND AFTER RESEARCHING THE MATTER FURTHER , REVIEWING A NUMBER OF DIY VIDEOS ON U TUBE AND FINDING THAT REPLACEMENT OF THE OIL PRESSURE SWITCH COST ABOUT $12.00 I ORDERED THE SWITCH. IT ARRIVED WITH IN A MATTER OF DAYS AND I COMPLETED THE TASK WITH IN AN HOUR. UNFORTUNATELY, AFTER TAKING THE CAR OUT ON A TEST RUN AND AFTER A TRAVELING ABOUT 5 MILES MY CHECK ENGINE LIGHT CAME BACK ON. I RETURNED HOME, LET THE CAR COOL DOWN AND AFTER A COUPLE OF HOURS HOOKED UP MY PT W2977 OBDII SCANNER AND WAS DISAPPOINTED TO SEE CODES P0523 & P0521 POP UP ONCE AGAIN. I AM AT MY WITS END AS I HAVE CHECKED EVERY POSSIBLE ELECTRICAL CONNECTION RELATIVE TO CAUSES FOR THESE TWO CODES BUT HAVE BEEN UNABLE TO LOCATE OR IDENTIFY ANY LOOSE CONNECTIONS. I ALSO CHECKED MY OIL LEVEL AS WELL AS A VISUAL OF THE MOTOR OIL ITSELF. THE MOTOR OIL APPEARS CLEAN WITH THE SAME APPEARENCE IT HAD WHEN THE OIL WAS CHANGED A MONTH AGO. I HAVE LOOKED HIGH AND LOW BUT COULD NOT FIND ANY OIL LEAKS NOR ANY EVIDENCE OF ANY POSSIBLE LEAKS. IN ADDITION I HAVE BEEN ABLE TO CLEAR THE CHECK ENGINE LIGHT A NUMBER OF TIMES USEING MY SCANNER HOWEVER IN EVERY INSTANCE AFTER TRAVELING BETWEEN 5 TO 10 MILES IT POPS UP AGAIN. THE CAR'S REGISTRATION RENEWAL IS DUE AT THE END OF THE MONTH AND REQUIRES A SMOG CERTIFICATE. NO WAY THAT IS GOING TO HAPPEN WITH MY CHECK ENGINE LIGHT CIRCUMSTANCE AND I FEAR THIS IS GOING TO END UP TO BE A VERY COSTLY REPAIR AND REGISTRATION RENEWAL.

No one can tell you with "Absolute Certainty" what the problem is and if they do, they are lying. There are too many factors that can trigger the codes, e,g, wires, sensors, control units, etc.
Based on my experience and reports from other techs, the most likely causes of the problem if you have both codes are:
- Engine Oil Pressure Sensor/Switch <-- You have already replaced this
- Engine Oil Level Sending Unit
- Valve Lifter Oil Filter

Also, make sure the engine oil condition and level is OK.

Thank you for your assistance and your time.
I spent all day researching online for a location of the oil pressure switch/sensor. Attempting to locate the osp sensor via the online instructions I had reviewed proved to be very frustrating and confusing. From under the car I was unable to locate anything that came close to resembling what I was looking for and I spent no less than an hour underneath the car searching for that ops sensor.
However, after giving up trying to find ops from under the car I popped the hood and continued my search from the top of the engine.
I found two strong possibilities that could be the ops. One sits at the rear of the engine, close to the firewall and positioned near the bottom of the block. But it looks more like a spark plug than other images of the ops. And the part at the rear of the engine only has two wires running out from the top of it. The wiring runs off into oblivion, somewhere.
The other part that could be the ops sits on the driver's side of the engine, positioned more about the middle and rear end of the block. It is not very easy to see due to a number of hoses and other obstructions that hide it. It resembles a number of images of the ops I viewed online but I am not 100 % sure that it is a ops.
I released the wiring harness and unclipped it from the top of the unit. Looking down from the top and into the part, there are 3 prongs that stick straight up. Obviously to accommodate and seat the wiring harness. There is a characteristic on the part that I not only found curious but has not been detailed in any images nor described in any detail as well.A type of yellow rubber boot covers the 3 prongs and sits snuggly against the walls to the very top of the unit. I was able to run my little finger around the top and down into the part as far down to where I could feel the prongs and identify the texture of the yellow boot.
Unfortunately, after spending all day up until dusk I am not able to say that I have convincingly located the oil pressure switch/sensor for my 2008 Buick Lacrosse Super (v8).
I suppose I should be happy that, after spending so much time under the motor as well as the time I spent looking from the top of the engine I did not find a single oil leak nor leakage of any kind coming out from the engine. I did find some residual oil sitting at the bottom of the oil pan. I wiped that off then checked the oil pan again, much later, before I pulled the car out of my garage and did not find any more oil as I had earlier.
Seeing that residual led me to check my motor oil. The level on the deep stick remained at about the same level it has been since my last oil change one month ago. In addition the oil appears to be in,about, the same and clean condition , as well.
I am still researching online resources that will tell me exactly where that is ops can be found, but no luck. I don't understand why it has been so difficult to find that information. I already have a pretty good idea how to replace it by finding diy vidoes. It has been so strange that I have been able to find diy vidoes for replacing the ops on most GMC's but not one for a 2008 Buick Lacrosse Super. I found this to be true for all other DIY projects for my vehicle. For instance my front wheel hubs and bearings needed to be replaced. It took forever to get the correct instruction on that project and a repair that should have taken a couple of hours turned out to be a two day nightmare. Due to one very simple yet very important detail that was not explained nor noted in the video. Many hours was spent trying to separate the worn out hub and brake disc from the rest of the assembly. All was going well up to that point and I tried everything I could think of. Spraying lubricant , 3 cans , did no good. Renting a special tool to pull out the unit only to have the tool finally snap away from it's grip was frustrating as hell. No amount of banging, prying or profanity did it. Finally, my wife came out hoping to ease my frustrating. As I sat, struggling with that unit my wife walked up and from behind me she said, "Hey, what's that"? She pointed out the head of one of those screws that requires one of those special fittings to tighten or loosen it. Instead of considering that option I kind of snapped at my wife and was a bit harsh on her for which I paid for that night and the following morning. So, I found the correct bit that fit perfectly into the head of that screw my wife pointed out the night before. Finally, with allot of persuation that screw began to loosen and after removing it entirely the unit easily slid off. The rest of the project went very smoothly and I had two, new front wheel hubs with bearing done by the end of the day. One simple screw so important to that repair was never acknowledged in that video and it cost me and is still costing me. I am hoping my wife will someday let that experience go unfortunately she seems to have a need to remind me about it, time to time.