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P0521: Oil Pressure Sensor → Switch/Range/Performance


P0521 is an OBD-II diagnostic code. It is activated when your vehicle’s DAB system detects that the value sent by the oil pressure sensor is outside the vehicle’s normal operating range. It is usually caused by a faulty oil pressure sensor.

The oil pressure sensor measures oil pressure mechanically, and converts that reading into a voltage signal that the PCM (Powertrain Control Module) converts into an oil pressure reading. This reading is what your oil light or oil pressure gauge uses to operate.

P0521 should be taken seriously. Although it is possible (and even likely) that the oil pressure sender or sensor is bad, there could also be a problem with the oil pressure. One of the causes of P0521 is a lack of oil pressure. Your engine can only last a few seconds without oil pressure.

P0521 Fast Data

  • The most common cause is a problem with the oil pressure sensor or circuit.
  • Should be taken very seriously
  • The most common symptom is an oil light or an incorrect oil pressure gauge reading.
  • P0521 seems to occur most commonly in GM vehicles (Chevy, GMC, Pontiac, Buick, etc…)

P0521 Diagnostic

P0521 Symptoms

These are the most common symptoms of P0521:

  • Low oil light/indicator Although P0521 is usually caused by a faulty oil pressure sensor, you should treat these gauges and warnings as if they were correct until you know.
  • Ticking and tapping- If your engine is ticking and knocking, chances are the oil pressure sensor is accurate and there is a problem with the engine or you need oil.
  • check engine light

P0521 Causes

P0521 is going to be caused by a problem with the sensor or sensor wiring (which would mean your engine is fine). Or it will be caused by a problem with oil level, viscosity, pressure or cleanliness.

Since proper oil flow is so critical to the engine, this code should be treated with respect.

These are the most common causes of P0521:

  • Low or no oil- The first thing you should do is check if there is oil in the engine. If the crankcase is empty or has very little oil, it may return the P0521 code. If this is the case, refill the oil, clear the code and that may fix the problem.
  • Low oil pressure- If the oil pressure level is too low, this code may appear. It should appear with the oil light, or with a low oil pressure gauge reading.
  • Dirty or incorrect oil If an oil change has not been performed for a long enough period of time, it may interfere with the oil pressure sensor, even if oil pressure is still present.
  • Oil pressure sensor wiring- P0521 indicates that the oil pressure sensor signal is out of range. This indicates a wiring problem.
  • Oil pressure sensor- The oil pressure sensor itself is most likely the cause of P0521, but looking at the oil and wiring first is a smart move.

P0521 Diagnostic

This P0521 diagnostic order is written (like everything on the site) for the DIYer who doesn’t have many special tools

1. Check the oil

The first thing you should do is check the oil level. If it is full, make sure it looks healthy. If it appears black or dirty, it may be interfering with the oil pressure sensor.

2. Inspect the wiring harness

Next, you should inspect the wiring harness that goes from the sensor to the PCM. If you have any damaged wiring, it could be the cause of P0521. Don’t forget to ensure that the wiring harness is still connected to the sending unit and is not damaged.

Wiring problems are one of the most common reasons this code occurs. The wiring is near the engine exhaust and can become brittle over time.

3. Manually check oil pressure

Assuming the oil level and wiring seem fine, the next would be to manually check the oil pressure. You can use a manual oil pressure gauge to hook up there and see if the oil pressure is where it should be. They are easy to use. Here is a great YouTube video that will show you exactly how to use this meter to check.

If the oil pressure on the gauge is correct, you will need to replace the oil pressure sending/sensor unit. If your oil pressure is low or non-existent, you’ll need to find out why.

Conclusion: P0521

Diagnosing P0521 is relatively simple. Knowing the actual oil pressure level makes it much easier. Feel free to leave a comment below if there is anything you want to add and good luck!


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