Error Code P0520 is defined as Engine Oil Pressure Sensor/Switch Circuit.  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.

Error Code P0520 means the PCM sees the value being sent by the sensor/sender is out of the normal range set by the manufacturer, indicating an electrically-related problem. The signal can be either too high or too low in relation to the specifications set by the manufacturer.

And if the red oil pressure light is illuminated, that means there could be a more serious problem as well.

Other related error codes include:

Common Symptoms

  • Low or high reading on oil pressure gauge (if equipped)
  • Oil pressure indicator lamp illuminated
  • Poor engine performance
  • Rough idling
  • Excessive engine noise
  • Premature engine failure from time to time

Possible Causes

Most common causes for this code are:

  • Defective oil pressure sensor/switch
  • Defective oil pressure sensor/switch wiring
  • Defective oil pressure due to dirty engine oil
  • Defective oil pressure due to lack of compression
  • Excessive resistance in the oil pressure sensor circuit

How to Check

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.

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.

The sensor must be proven defective via digital multi-meter test before being replaced.

How to Fix

Depending on the diagnosis, common repairs for this code include:

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

The usual cause of this code is a defective pressure sensor, as poor engine performance can also result in poor oil pressure. Thus, before considering of replacing any parts, it is worth to consider other mechanical failures.

This code is a serious problem, as low oil pressure can cause the crankshaft and its connecting rod and bearings to seize, which reduces the engine’s performance.

PCM replacement is more of a last resort, which must be done only after proper diagnosis.