GMC Yukon P0521: Oil Pressure Sensor Switch → Performance/Range

P0521 This is an OBD2 diagnostic Code that is activated when you GMC Yukon detects that oil pressure sensor value is not within its normal range.

This is usually caused by an oil pressure sensor problem or an oil system issue. It should be immediately diagnosed and repaired.  It is possible, and even probable that an oil pressure sensor/sensor is defective. However, it could also indicate a problem in the oil pressure.  

Your Yukon’s 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.  The oil warning light is activated when this reading appears on the oil pressure gauge.

P0521 Quick Facts

• Most often caused by an issue with your Yukon’s oil pressure sensor or circuit
• You should take P0521 very seriously
• Most common symptoms are the oil light and an incorrect oil pressure gauge reading.
• Simple to diagnose

P0521 Symptoms:  GMC Yukon

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

• Low Oil Light/Gauge Although P0521 can often be caused by an oil pressure sensor problem, it is important to treat readings from your oil gauge or low oil warning as if they were correct.
• Ticking, Knocking and Tipping 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– That’s why you are here.

Yukon P0521 Causes

Problems with sensor wiring or the sensor are what will cause P0521. Your engine should be fine.  Or it is going to be caused by an issue your Yukon’s oil level, viscosity, pressure, or cleanliness.  

Proper oil flow is vital to an engine's performance. This code must be respected and followed.

These are some of the leading causes for P0521.

• Low oil consumption or none The first thing that you should do is check to see if there is oil in your Yukon’s engine at all.  It can also throw the P0521 error if it is very low or empty.  This can be fixed by filling the oil with more, clearing the code and resetting the crankcase.  
• Low oil pressure The code will appear if oil pressure drops too low.  This code should be accompanied by the oil light or low oil pressure readings from the oil gauge.  GMC Yukon Low oil pressure diagnosis
• 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.  It indicates that the wiring is not working properly.
• Oil Pressure Sensor It is possible that the problem may be caused by an oil pressure sensor. However, it's smart to first look at the wiring and oil.

GMC Yukon Diagnostics 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. Examine 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 black or grimy.

2. Examine the Wiring Harness

Next, you should inspect the wiring harness running from the oil pressure sensor to the PCM.  It could also be the cause of P0521.  Don’t forget to make sure that the harness is still plugged into the sending unit and undamaged.  

One of the most common reasons this code is thrown is because wiring problems are common.  The wiring is close to the Yukon’s exhaust and can get brittle over time.

3. Manually check your oil pressure

If the wiring and oil levels are in good condition, you can manually test the oil pressure.  A Oil pressure can be manually adjusted gauge to see if it’s where it needs to be.  They're easy to use.  Here’s a Great 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.  They’re cheap.  If there is low or no oil pressure, you’ll need to figure out why.

Conclusion

It’s relatively straightforward diagnosing P0521.  This is made easier by knowing the exact oil pressure.  If you have any suggestions, please leave them below. Good luck with your GMC Yukon.