P0521 code: No Oil Pressure Reading

Troubleshooting a P0521 code with No Oil Pressure Showing On The Instrument Cluster

The P0521 code is defined as “Engine Oil Pressure Sensor/Switch Range/Performance.” Essentially, this code is triggered when the engine control module (ECM) detects a discrepancy between the actual oil pressure and the expected value. The oil pressure sensor, also known as the oil pressure switch, monitors the engine’s oil pressure and sends this information to the ECM. If the sensor provides a reading that is outside the expected range or is inconsistent, the ECM will log the P0521 code. Shops are reporting a large number of GM engines with a P0521 and no oil pressure showing on the instrument cluster.

The problem is common on 5.3L, 6.0L, and 6.2L engines equipped with active fuel management (AFM) systems. The P0521 engine oil pressure (EOP) sensor performance trouble code can be caused by a faulty sensor, a stuck AFM oil pressure relief valve, or sludge buildup in the engine. Here’s how to diagnose and fix a P0521 no oil pressure on gauge condition

Test the oil pressure sensor

A clogged screen in the oil pressure sensor can cause a P0521 code

Locate the oil pressure sensor at the rear of the engine block. Disconnect the electrical connector and then remove the sensor using an oil pressure sensor socket. Next, remove, replace, or clean the filter located under the sensor.

Attach a mechanical oil pressure gauge and start the engine. If the oil pressure reads fine on the mechanical gauge, replace the sensor. If the oil pressure is still low or at 0, move on to the next step.

Check the oil pressure at the oil filter

Remove the engine oil filter. Attach an adapter and then your mechanical oil pressure gauge. Then, run the engine and compare the oil pressure reading to the one from the sensor port. If the oil pressure at the oil filter adapter is good but the pressure reading at the oil pressure sensor is low, that’s a sign of a partially stuck open AFM oil pressure relief valve or sludge buildup in the engine.

If the oil pressure is low at both the sensor port and the oil filter adapter, you may have an oil pump issue, a stuck oil pump pressure regulator valve, sludge buildup, or an AFM relief valve that’s stuck in the wide open position.

©, 2019 Rick Muscoplat