Error Code P0521 is defined as Engine Oil Pressure Sensor/Switch Range/Performance.  This is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, particularly those made since 1996 up to present. It is particularly common among Cadillac, Chevrolet, Dodge, GMC, Mercedes Benz, and Pontiac models. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) is the vehicle’s computer system which controls multiple controls, electronics, and sensors. One of these sensors is the ‘Oil Pressure Sensor’ or ‘Oil Pressure Sender’ which detects the amount of (mechanical) oil pressure in the engine. It relays information through voltage reading value to the PCM. For some vehicles, oil pressure value is relayed to a gauge in the instrument cluster, showing the driver the oil pressure. Sometimes, however, there is no gauge; rather, there will be a warning light to notify the driver about the problem.

When Error Code P0521 is triggered, that means the PCM has determined an unexpected value in engine oil pressure sender/sensor, which is out of its normal range or could be fixed when it should fluctuate. This code could either be mechanical or electrical, but in many cases it points to the latter.

Other related error codes include:

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:

  • Too high or too low reading on oil pressure gauge
  • Oil pressure indicator lamp activated

Possible Causes

  • Old dirty oil (overdue for an oil change)
  • Low oil level in the engine
  • Low oil pressure
  • Faulty connector or wiring in the oil pressure sender circuit
  • Defective oil pressure sender/sensor

How to Check

As said earlier, this code could be a result of a mechanical problem, which means it must be addressed as soon as possible.

A good starting point in diagnosing this code is with the use of TSB (technical service bulletin) for the vehicle’s specific make and model

As with other oil pressure issues, the engine’s oil and levels must be checked first in addressing this code. Check the oil level using a dipstick and make sure there is an adequate amount of oil in the engine. Oil filter and drain must not be leaking. A leak can cause low or no oil pressure. If it seems like the oil has surpassed its change interval, then it should be changed, along with a new filter. There are also cases where technicians forget to tighten the filter enough.

Technicians would likely do two things for this code – use mechanical oil pressure tester installed on the engine to get the actual physical oil pressure. Then, they will compare their findings with the values shows by the PCM. If you have a scan tool and an oil pressure gauge, then this is the best option.

If you have already ruled out the problem with oil pressure, then the issue could be caused by either within the sensor or the connectors or wirings.

Use DVOM to check the sensor. If it fails to meet the specs of the manufacturer, then it must be replaced. Replacing sender/sensor will most likely fix the problem.

Next, the pressure sensor must be visually checked to ensure it is properly seated and there are no wiring damages. Broken, burnt, frayed, loose, or exposed wirings must be fixed, either through repair or replacement. Electrical connections must also be tight, and without oily or contaminated problems.

How to Fix

In most cases, simply changing out the oil and resetting the oil pressure sensor can fix this problem. Other repairs include:

  • Repair or replacement of faulty oil pressure sensor wirings and connectors

As said earlier, this code is considered serious and must be addressed as soon as possible, as it could lead to serious damage to the engine. Also, this may cost a lot to fix.