Hi I'm having this message, 'low oil pressure' when temp go to suitable temperature my car Peugeot 407

The service and repair manual will provide you step by step help to locate and fix the problem easily on your own and you will get the manual from the given link https://toolsnyou.com

low oil level in the sump and low coolant level in the radiator
could be excessive oil i the transmission
run the fault codes to determine other failures

Worn main and rod bearings on the crank shaft. This is what creates the oil pressure. When the get worn they start loosing pressure. Also when the oil gets hot, it gets thinner, causing more lose of pressure.

https://www.google.co.uk/search?q=Peugeot+407+battery&oq=Peugeot+407+battery&aqs=chrome..69i57&sourceid=chrome&es_sm=122&ie=UTF-8

Are you running oil of proper viscosity for temperatures in your area?

NO "FIX IN A CAN" WILL PERMANENTLY SOLVE A RACK LEAK! MORE THAN LIKELY...IF EITHER END BOOT IS LEAKING...THEY ARE GENERALLY NOT REBUILT (EXCEPT BY O.E.M. SUPPLIERS). YOU ARE MOST LIKELY GOING TO NEED A NEW OR RE-MANUFACTIURED STEERING RACK.....SORRY!

According to what you describe, it is possible that the valve cover on the cylinder head and the oil pan are dirty ,It is prudent to uncover and check

Peugeot 407 Automatic Gearbox: oil low pressure?

If by pulsing you mean that the idle is fluctuating up and down, this is caused by oil/sludge build up in the throttle valve. To rectify this remove the intake pipe at the throttle valve. Use engine cleaner/degreaser on a rag to clean out throttle valve around throttle butterfly. Open butterfly manually to assist access. The oil pressure light coming on is usually caused by the oil pump pick up becoming blocked by carbon and sludge in the oil sump. If you have a suitable oil pressure gauge, check the oil pressure at the oil switch. Oil pressure should be 3.5- 4 bar at 2000 rpm at operating temperature. If pressure ok, Pressure switch may be faulty. If pressure low you will have to remove oil sump and clean out or replace oil pump pick up. If not done, may result in major engine damage. Sludge and carbon build up caused by oil not being changed often enough. Best to use a synthetic oil.

I am not familiar with the 407 but I would think it is a HDi, if so what you describe is an air leak from a pipe from the pressure side of the turbo, I have had this on a Saab, in that case there was an over pressure switch under the dash and the pipe fell off. Look at the top of the engine, on the inlet side there will be a pipe from the inlet trunking or manifold, it should (maybe with a tee piece in there) go through the bulkhead