P0521 is an OBD-II diagnostic code. 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 is typically caused by a bad oil pressure sensor.
The oil pressure sensor measures the 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. While it is possible (and even likely) that the oil pressure sender/sensor is bad, there could also be a problem with the oil pressure. One of the causes of P0521 is no oil pressure. Your engine can only last a few seconds with no oil pressure.
P0521 Quick Facts
- Most often caused by an issue with the oil pressure sensor or circuit
- Should be taken very seriously
- The most common symptom is the oil light or an improper oil pressure gauge reading
- P0521 seems to occur most commonly in GM vehicles (Chevy, GMC, Pontiac, Buick, etc…)
Here are the most common symptoms of P0521:
- Low Oil Light/Gauge- While P0521 is often caused by a bad oil pressure sensor, you should treat these gauges and warnings like they are correct until you know better.
- Ticking and 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.
- Check Engine Light
P0521 is going to be caused by an issue with the sensor or sensor wiring (which would mean your engine is fine). Or it is going to be caused by an issue with the oil level, viscosity, pressure, or cleanliness.
Since proper oil flow is so critical to the engine, this code should be treated with respect.
Here are the most common causes of P0521:
- Low or No Oil- The first thing that you should do is check to see if there is oil in the engine at all. If the crankcase is empty or really low on oil it can throw P0521. If this is the case, fill the oil back up, clear the code, and that may fix the problem.
- Low Oil Pressure- If the oil pressure level is too low, this code can show up. It should show up with the oil light, or a low reading from the oil pressure gauge.
- Dirty or Wrong Oil- 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- P0521 indicates that the signal from the oil pressure sensor is out of range. This indicates a wiring issue.
- Oil Pressure Sensor- The oil pressure sensor itself is very likely to be the cause of P0521, but looking at the oil and wiring first is a smart move.
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. Check the Oil
The first thing that you should do is check the oil level. If it’s full make sure that it looks healthy. If it appears to be black or grimy, it may be interfering with the oil pressure sensor.
2. Inspect the Wiring Harness
Next, you should inspect the wiring harness running from the sensor to the PCM. If it has any damaged wiring, that could be causing P0521. Don’t forget to make sure that the harness is still plugged into the sending unit and undamaged.
Wiring issues are one of the more common reasons that this code is thrown. The wiring is close to the engine exhaust and can get brittle over time.
3. Manually Check The Oil Pressure
Assuming that the oil level and wiring look fine, the next thing to do would be to manually check the oil pressure. You can use a manual oil pressure gauge to hook in there and see if the oil pressure is where it needs to be. They are easy to use. Here’s a great YouTube video that will show you exactly how to use this gauge to check.
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.
It’s relatively straightforward diagnosing P0521. Knowing the actual oil pressure level makes it a lot easier. Feel free to leave a comment below if there is something that you would like to add and good luck!