Stop engine. oil engine blinks, says 'stop engine, oil pressure low' already changed the sensor, the oil sending unit?? warning is not continuous, comes on and goes off.

1. no year told.
2. no cars engine told, or petro or diesel fuel or what?
   
3. no country told
4. no miles on Odometer told. (a hard case this to do)

oil pressure low , needs to be checked out in a shop! fast.

1. using wrong oil there or is way too low on the dipstick
2. water or coolant in the oil is super bad, looks MILKY
3. gas in the oil ,sniff sniff dip sticks smells of gas/petrol?
4. weak oil pump
5. super worn engine bearings,cam/crank/rods.
6. bad defective oil sender we test pressure with a real gauge 1st.
7. OMG oil filter fell off or loose is oil leaking to the ground?
8. on old cars we check engine oil level every fuel fill up.. or fail.

The low oil pressure warning lamp will illuminate anytime the ignition switch is turned to the ON position without the engine running. When the engine is running, the light also illuminates if the engine oil pressure drops below a safe oil pressure level. To test the system, perform the following:
If the oil pressure light does not work, perform the following:

1. Turn the ignition switch to the ON position.
2. If the lamp does not light, check for a broken or disconnected wire around the engine and oil pressure sending unit switch.
3. If the wire at the connector checks out OK, pull the connector loose from the switch and, with a jumper wire, ground the connector to the engine.
4. With the ignition switch turned to the ON position, check the warning lamp. If the lamp lights, make sure the oil pressure switch is properly grounded in the cylinder block, and if so replace the oil pressure switch. If the lamp still fails to light, check for a burned out lamp or disconnected socket in the instrument cluster.

To diagnose an oil pressure light that stays on, perform the following:

1. Check the engine oil level and top off as necessary. If the engine was 2 or more quarts low on oil, test start the engine after topping off the oil level and recheck the oil pressure light operation. If the light stays on, stop the engine immediately and go to the next step.
2. Disconnect the wire at the sending unit, then turn the ignition switch to theON position. If the light remains on, check the wire from the sending unit to the gauge for being shorted to ground and repair as necessary. If the light goes out, turn the ignition switch OFF and go to the next step.
3. Replace the oil pressure sending switch with a known good switch.
4. Start the engine and check the oil pressure light operation. If the light stays on with the engine running, stop the engine immediately to avoid severe engine damage until the cause of the problem can be determined.

WARNING
If the oil pressure light remains on while the engine is started, stop the engine immediately. Do not operate the engine until the cause of the problem can be determined. Operating an engine with low oil pressure will cause severe internal damage.

Possible causes for an oil pressure light to stay on are:


Pinched or grounded sensor wireDefective oil pressure sending unitRestricted or severely leaking oil filterExcessive internal engine bearing clearance.Insufficient or severely contaminated engine oilBlocked oil pump pickup screen or severely worn oil pump

The pressure regulator in the oil pump may not be working, the idle speed may be too low and there may be a lot of wear on internal engine parts lowering oil pressure

Possible causes
- Low oil level or motor mechanical fault
- Faulty oil pressure sensor
- Oil Pressure Sensor harness is open or shorted
- Oil Pressure Sensor circuit poor electrical connection

When is the code detected?
The P0521 is detected when the signal sent from oil pressure sensor to PCM goes out of range.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Oil pressure warning light ON.
P0521 Chevrolet Description
The PCM continuously monitors the engine oil pressure. The Oil Pressure Sensor/Switch sends a signal to the PCM when the engine is running.

see this tips and fix it. God bless you
The oil pump supplies oil to lubricate your engine. If the oil pump is worn or is not turning, the engine will suffer a loss of oil pressure, which may result in engine damage or engine failure.
The first sign of trouble may be a low oil pressure warning light, a drop in the normal reading on you oil pressure gauge (if your car has one), or the appearance of ticking or clattering sounds from your engine.
As a rule, most engines only need about 10 PSI of oil pressure for every 1,000 RPM of engine speed. Oil pressure will read higher than normal when a cold engine is first started because the oil is thick. Oil pressure will gradually drop as the engine warms up and the oil thins out. So normal oil pressure on a warm engine cruising down the highway is typically 30 PSI up to 45 PSI.
SYMPTOMS OF OIL PUMP TROUBLE
The first thing you should do if any of these symptoms occur is to stop your car, turn off the engine, let it sit for a few minutes, then check the oil level on the dipstick. If the oil level is at or below the ADD line, add a quart of oil to bring the level back up to the full mark. Add as much oil as is needed to raise the level to the full mark. Then restart the engine. If the warning light remains on, or the oil pressure reading does not climb back up to its normal range, or the engine noise does not go away, you may have a bad oil pump.
The other possibilities include a bad oil pressure sending unit, or a problem with the oil pressure warning light circuit or oil pressure gauge.
OIL PRESSURE SENDING UNIT
If the engine is NOT making any unusual noises and seems to be running normally, and the oil level on the dipstick is FULL, but you are still getting a low oil pressure warning light or low gauge reading, the fault could be a bad oil pressure sending unit.
The oil pressure sending unit is mounted on the engine block. On some applications, there is a spring-loaded pressure-sensitive diaphragm with a switch inside the sending unit. This switch completes the circuit to the low oil pressure warning light if oil pressure drops below a certain threshold. The unit may stop working if the diaphragm inside fails, if the switch is stuck, if the small hole that allows oil to enter the sending unit becomes plugged, if there is a loose, corroded or broken wiring connector at the sending unit, or there is a fault in the wiring circuit between the sending unit and warming light.
On vehicles that have an oil pressure gauge (electronic, not mechanical), the oil pressure sending unit has a small rheostat inside that sends a variable voltage signal to the oil pressure gauge when the diaphragm moves. A worn spot on the rheostat or any of the other problems just described for the simple pressure-type oil pressure switches can cause a problem.
FORD'S FAKE OIL PRESSURE GAUGE
On many Ford vehicles that were built from 1980 through the 1990s, the oil pressure sending unit has two switches, a low pressure and a high pressure. These vehicles also have an oil pressure gauge, but the reading on the gauge is not a true indication of real oil pressure. As long as the pressure to the sending unit is between high and low, the gauge will read normal. If oil pressure drops and trips the low pressure switch, the dash gauge will now read low. Or, if oil pressure goes up and trips the high switch inside the sending unit, the dash gauge will read high. Consequently, don't rely on the oil pressure gauge for an accurate reading in these vehicles. It is only a gross indication if the oil pressure is low, normal or high.
OIL GAUGE PROBLEMS
If the engine is NOT making any unusual noises and seems to be running normally, the oil level on the dipstick is FULL, and you have replaced the oil pressure sending unit but are still getting a low oil pressure reading on the dash gauge, the fault could be in the wiring circuit between the sending unit and gauge, or the gauge itself might be bad.
Check the wiring connections on both ends as well as wiring continuity between the sending unit and gauge. If no wiring faults are found, hook up a pressure gauge directly to the oil pressure port on the engine and check oil pressure with the engine running. If the engine-mounted gauge shows normal oil pressure but the dash gauge is reading low, the problem is a bad dash gauge.
On the other hand, if the engine-mounted pressure gauge reads low and you have done all of the above, chances are the oil pump is worn, or it is not picking up enough oil because of a restriction or blockage in the pickup screen in the bottom of the crankcase.
OIL PUMP PICKUP PROBLEMS
The pickup tube has a screen on the end to prevent large chunks of anything bad that ends up in the crankcase from being sucked into the pump. But we are talking BIG chunks of debris, not normal wear particles or carbon or dust or other microscopic-sized abrasive particles that can cause pump wear over time.

Verify that the engine has the proper amount of oil. The inertia from accelerating may be moving the oil in the oil pan away from the sensor and causing it to send a signal, then when you slow the oil levels out and the sensor go's off. I've had this happen alot with a taurus that I owned. The simple solution was to top off the oil to the correct level and the sensor did not come on again (until it ran low again, had a leaky oil plug on oil pan).

Could be a few things, first Get it checked with a mechanical gauge to test low motor oil, clogged oil filter, bad oil pump, clogged oil sump (pick up tube) or bad oil sending unit. Then replace sending unit sensor.

Normally, if you get a oil warning light signal (flashing) could be a few things related to it. Number one, you are low on oil. Check your oil level and make sure it is at full level. Number two, is possibly oil filter is dirty, ( time for service,oil change) or problem with oil pump or oil pump pressure. BUT I would first start with checking oil level and then maybe a oil change.

low on oil or sending unit bad or sump in oil pan stopped up or bad oil pump

Check your oil, it may be low if not the oil pressure needs checked. The sending switch could be bad or you have low oil pressure. If you have low oil pressure have it fixed ASAP. The loss of oil pressure can cause severe engine damage.