P0521: Oil Pressure Sensor → Switch/Range/Performance

OBD-II diagnostic code P0521.  It is triggered when your vehicle’s OBD system detects that the value being sent from the oil pressure sensor is out of the normal operating range of the vehicle.  It's usually due to a low oil pressure sensor.

Oil pressure sensors measure the oil pressure and then convert that voltage signal into an oil pressure reading.  This is the reading that your oil light (or oil pressure gauge) uses.

It is important to take P0521 very seriously.  Although it's possible and likely that your oil pressure sensor is defective, it may also indicate a problem with your oil pressure.  P0521 can be caused by low oil pressure.  Without oil pressure, your engine will only last for a few seconds.


Índice de Contenido
  1. P0521 Quick facts
  2. P0521 Symptoms
  3. P0521 Causes
  4. Diagnoses P0521
    1. 1. Take a look at the oil
    2. 2. Check the Wiring Harness
    3. 3. Manually check your oil pressure
  5. Conclusion: P0521

P0521 Quick facts

  • Most likely, the problem is with an oil pressure sensor circuit.
  • You should take it very seriously
  • Most common symptoms are the oil light and an incorrect oil pressure gauge reading.
  • P0521 seems to occur most commonly in GM vehicles (Chevy, GMC, Pontiac, Buick, etc…)


P0521 Diagnosis


P0521 Symptoms

These are some of the symptoms that P0521 is most commonly associated with:

  • Low oil light/Gauge P0521 may be due to a poor oil pressure sensor. You should still treat warnings and gauges as if they were correct, until you realize better.
  • Ticking or Knocking - If your engine is ticking and knocking, it’s likely that the oil pressure sensor is accurate and there’s a problem with the engine or you need oil.
  • Make sure your engine light is on


P0521 Causes

The problem with your sensor wire or sensor sensor is what causes P0521. This would indicate that your engine is in good condition.  Oder it could be caused by an oil level problem, viscosity and pressure issue, or cleanliness.  

Because proper oil flow is crucial to an engine, it should be treated as such.


These are some of the leading causes for P0521.

  • Low oil consumption or none Check to ensure that there is enough oil in the engine.  The crankcase can be thrown P0521 if the oil level is very low.  Clear the code and fill up the oil.
  • Low oil pressure This code may appear if the oil pressure is too low.  The oil light should indicate it, as well as a low reading on the oil pressure gauge.
  • Wrong oil or dirt? If there hasn’t been an oil change for a long enough period of time, it can interfere with the oil pressure sensor, even if there still is oil pressure. 
  • Oil Pressure Sensor Wiring The signal from an oil pressure sensor has gone out of range. P0521 is the result.  This is a signal that there are wiring problems.
  • Oil Pressure Sensor Although the P0521 problem is most likely caused by the oil pressure sensor, it is worth looking into the wiring and oil first.


Diagnoses P0521

This P0521 diagnosis order is written (like everything on the site) for the DIY guy who doesn’t have a lot of specialty tools. 


1. Take a look at the oil

First, check your oil level.  If it’s full make sure that it looks healthy.  You may have an oil pressure sensor problem if the lid appears blackened or grimy.


2. Check the Wiring Harness

Next, you should inspect the wiring harness running from the sensor to the PCM.  You could have P0521 if the wiring is damaged.  Don’t forget to make sure that the harness is still plugged into the sending unit and undamaged.  

This code can be thrown because of wiring issues.  Over time, the wiring can become fragile near the engine exhaust.


3. Manually check your oil pressure

If the wiring and oil levels are in good condition, you can manually test the oil pressure.  There are two options: Oil pressure can be manually adjusted You can use the gauge to check the oil pressure.  These are simple to use.  Here’s a Amazing YouTube video This will demonstrate how you can use the gauge to test.

If the oil pressure from the gauge reads ok, you’ll need to replace the oil pressure sending unit/sensor.  If there is low or no oil pressure, you’ll need to figure out why.


Conclusion: P0521

It’s relatively straightforward diagnosing P0521.  This is made easier by knowing the exact oil pressure.  You can leave comments below if you have anything to share.

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