Normal oil pressure range

2.9 to 3.9 bar at 3000 rpm is fairly general for the Nissan range including turbo diesel, though the pressure isn't listed for the td27 engine. I doubt it would be more or less than the others.
I notice one Nissan commercial vehicle engine where 3.0 bar at 2000 rpm is specified.

The oil pressure test should be carried out at normal operating temperature.

Do not drive the truck until the issue is resolved.

1. Make sure the oil is at the proper level in the engine with the correct spec oil for the pickup. Oh it is normal for the oil pressure to be a little low at idle and go up to the normal range as the engine rpm goes up to normal operating range.

2. It could be either a real problem or a problem with the oil pressure indicator. To verify which connect a mechanical test pressure gauge of the proper range say a 0-100 psig scale to the point where the oil pressure sensor is connected. After it is connected test run the engine for a short period. If the pressure shows normal replace the oil pressure sensor. If the gauge confirms the low oil pressure then you have a serious issue in the engine. It could be:

1. Bad oil pump or oil pressure relief valve

2. excessive clearance in the bearings due to high miles.

Rated pressures are always on the tire. Usually max pressure is 44lbs, cold

Normal operation is about 35lbs, for most passenger cars

Low oil pressure at idle can be caused by an engine with worn rod or main bearings due to (usually) high mileage . This however does not mean the engine is still not serviceable as long as the oil pressure is low only at idle. The pressure should at minimum get into the normal range at anything above idle speed.Not much oil pressure is really necessary at LOW speed. At low speed, as long as there is oil getting to the bearings, even at low pressure, you are OK. In a high mileage engine the oil pressure is often low at idle simply because the oil pump is turning slowly and cannot maintain higher pressure between the larger than normal crankshaft and bearing clearances. As speed increases the pump turns faster and supplies more oil and the pressure should go higher. Low pressure as long as it is only at idle is not a problem. However at higher speeds the pressure should be in the normal range. Such a worn engine can benefit from higher viscosity (thicker) oil such as 20W-50 in above freezing weather and 10W-40 in winter. That will increase idle pressure and the thicker oil film maintains a better film between the worn parts

Your oil pressure will flucuate with the rpm of your engine. It is generally higher also when the engine is cold as the oil is thicker. This is normal as long as your oil pressure stay in the normal operatting range.

yes it might work if u flush it, give it a try

either the oil pressure sender is defective or the pressure relief ball valve in the oil pump is sticking, my money would be on the oil pump pressure relief valve ball sticking.

Replace the oil pressure sensor to fix this problem!

It can be either electrical short or mechanical trouble.  Have the oil pressure test done on the car at two different sites - one in the engine block near the valve cover and another in the top of oil filter housing.  If the pressure is in the normal range, then it's electrical short.  If it isn't in the normal range, it is either something is blocking the oil from circulating or needs bearing replacement.

A quick (but not accurate) test would be to have the car running and check the oil level.  If the oil level remains constant, then the oil might not be circulating (which is why manuals often say check the oil when the engine is not running).  Be careful not to drive it if it looks like that the oil isn't circulating because it could lead to serious damage (in other words, engine rebuilding with bearing replacement).