The oil pressure problem is typical strictly for N43 series engines. The six-cylinder engines with electronic oil pressure management, these problems are observed in much fewer cases.
The story of today’s patient. The owner of the car went to change the oil and oil filter. The service, who performed the maintenance, noticed error messages regarding oil pressure recorded (at least the service employees have said so). The sensor was replaced (as if OEM), but the situation worsened. The red oil pressure icon appears in KOMBI (typically – after reducing the RPM till idle). At that moment, I was asked to inspect the car to understand, what went wrong, and what to do.
As usual, let’s start the inspection with the error message list:

Yes, as we see – the error messages regarding oil pressure are recorded. Let’s see the freeze-frame of the error message:

The error message is recorded both for a cold and warm engine; on the go and on idle. We see also that the measured value of the pressure is almost two times lower than the required pressure.
Note: The pressure should be significantly lower for at least 5 seconds to record this error message.
Conclusion – the problem is entirely sporadic, without exact conditions. Yes, in two of 3 cases, the idle and warm engine were figuring, but – who knows, maybe for 33 times after these two, the obstacles were utterly different.
But what about the error message regarding the oil pressure sensor? Here is the History memory of the error messages:

Yes, really – there has been an error regarding the oil pressure sensor readings. So, we have to understand – are there still any problems with measuring the oil pressure (for example, wires, connectors, theoretically – DME ADC input), or – actually there was another problem (and where it was).
Next stage – check live data. As the error message was recorded for the cold engine two times, we started the inspection of the data precisely with the cold engine. Here, the engine’s RPM required and measured pressure:

As we see, DME can maintain the required pressure (measured is indicated in the relative measuring unit, 1000 hPa should be added to it) – DME works in closed-loop mode, but the PWM of the valve looks strange:

In the case of a correctly working valve, PWM is around 40% (about 50% in the case of six engines), but here – 60 .. 70%. So high PWM value means that the DME opens the overflow valve to reduce the oil pressure. Logical conclusion – I doubt the oil pump has suddenly “got damaged” so that it started to produce 3 .. 10 times larger flowrate. The explanation is that the valve is (at least partly) stuck in the closed position or significantly clogged.
When the engine warms up longer, the situation changes rapidly. After a moment, PWM has already dropped to 25 .. 30%!

And the actual (measured) oil pressure already for several hundreds of mBar below the required – DME clearly has problems maintaining the oil pressure. So now the situation is the opposite – the valve is closed by electronics, but the oil pressure – does not reach the necessary.
Increasing the RPM of the engine, exciting effects could be seen. 2 .. 5 seconds after increasing RPM, PWM supplied to the valve started to increase/jitter, reaching 45 .. 50%. If RPM is reduced till idle at this moment, the PWM of the valve drops to 20 .. 25% (the valve received a command to close), but the measured pressure was reduced.
Also, these symptoms indicate the problems of the valve – it is stuck in fixed positions.
Of course, I can not claim 100% now, but I assume that the error message regarding oil pressure sensor indications was incorrect. Obviously, due to the strong sticking of the valve, the readings of the pressure sensor were so strange that DMDE drew an erroneous conclusion that the sensor was to blame. This could be when the reading of an error message drives wrong decisions and unjustified expenses.
Causes of this defect: rare oil change intervals, low-quality oil, and filter. Oil residues, dirt, and slag clog the valve. These valves can’t be cleaned or repaired. The only solution – is a new OEM valve.
Some more comments regarding N43 and the oil pressure problems.
a. unfortunately, management of INPA required oil pressure in the Service block menu for N43 series engines (using 2.023 loader for N53) is not working;
b. INPA diagnostics module (using loader 2.023 for N53) did not work in the current case. The statement that required conditions are not reached has been received in both cases. After a long battle, I managed to activate the diagnostics module (I was able to do this after clearing of errors and all adaptations);
c. instead, the N43 profile, included in INPA, does not include nor test module, neither the diagnostics module, not even the appropriate live data.
When trying to use ISTA to solve this problem, it is interesting that the oil pressure problem has a very low priority!

When choosing a test plan for this problem, the following menu is offered:

The most interesting is precisely the System test. I assume that initial diagnostics with INPA have been performed (it is clear, does the DME measures the pressure, tries to manage it, etc.), so let’s see, will the test block, which very well performs for the N53 series engine, will work here also.
Short comment regarding the ISTA System test module:
a. in the first stage, the test module switched in the mode of maximum pressure and command to develop in a range from idle RPM to 1500 RPM;
b. during next stage, the test module by different RPMs (idle; 1500 RPM) commands to maintain exact oil pressure (2000; 3000 hPa).
The BMW tool should be connected to this test module – a digital manometer, which readings are displayed by ISTA. Significant lack of this test block – neither electronically measured oil pressure is shown during the test nor required (by DME)! Yes, there are moments when the value of the required pressure is indicated in the description text, but live data of this parameter are not present. This is a significant lack of this test block.
I have to admit – ISTA will be helpful because the submenu of the sensor of the valve offers the connection schematics of these components and gives information regarding the type of the signal/values (in the case of the valve test, the connection of the oscilloscope is intended).
And finally, unfortunately, ISTA (unlike INPA) does not offer the data if required and actual oil pressure in live time (in the Call-up function list, only the measured oil pressure is available). But the most important – PWM data of the pressure regulating valve is not available! In this regard, INPA gives more information – in case of necessity, you can perform a test drive to check if DME can maintain the required oil pressure in different conditions.