For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC 0521: Engine Oil Pressure (EOP) Sensor

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Engine Oil Pressure 5-Volt Reference Circuit | P0522 | P0522 | -- | P0521
Engine Oil Pressure Sensor Signal Circuit | P0522 | P0522 | P0523 | P0521
Low Reference | -- | P0523 | -- | P0521

### Circuit/System Description

The engine oil pressure (EOP) sensor changes voltage based on engine oil pressure, and it is a 3-wire sensor comprising of the signal circuit, the low reference circuit and the 5-volt reference circuit. The engine control module (ECM) supplies 5 volts to the EOP sensor via the 5-volt reference circuit and provides ground via the EOP low reference circuit. The ECM monitors the signal circuit of the EOP sensor to determine if the engine oil pressure sensor voltage is within the normal operating range of approximately 1-4 volts. When the oil pressure is high, the sensor voltage is high, and the ECM senses a high signal voltage. When the oil pressure is low, the sensor voltage is low, and the ECM senses a low signal voltage. The ECM sends the EOP information to the instrument panel cluster (IPC) via the GMLAN serial data circuit.

### Conditions for Running the DTC

#### Condition 1

The engine idles at least 640 RPM, and the EOP sensor detects high oil pressure.

#### Condition 2

• | The calculated engine oil temperature is higher than 80°C (176°F).

• | The engine runs greater than 1,520 RPM, and the EOP sensor detects low oil pressure.

The DTC P0521 runs continuously once one of the above conditions is present for greater than 10 seconds.

### Conditions for Setting the DTC

• | The engine oil pressure (EOP) is greater than 880 kPa (127.6 psi).

• | The engine oil pressure (EOP) is less than 8 kPa (1.16 psi).

• | The above condition is present for 10 seconds.

### Action Taken When the DTC Sets

• | The ECM records the operating conditions at the time when the diagnostic test fails. The ECM displays this information in the Failure Records on the scan tool.

• | The IPC illuminates the EOP indicator.

### Conditions for Clearing the DTC

• | The DTC becomes history when the conditions for setting the DTC are no longer present.

• | The history DTC clears after 40 malfunction free warm-up cycles.

• | The ECM receives the clear code command from the scan tool.

### Reference Information

#### Schematic Reference

• | Instrument Cluster Schematics

• | Engine Controls Schematics

#### Connector End View Reference

• | Component Connector End Views

• | Engine Control Module Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

### Circuit/System Verification

With the scan tool installed and the engine idling, verify if the Engine Oil Pressure (EOP) Sensor parameter displays within the specified range of 0.7-2.8 volts or 8 kPa (1.16 psi) and 880 kPa (127.6 psi).

### Circuit/System Testing

1. Ignition ON, and the engine idling, verify if the Engine Oil Pressure (EOP) Sensor parameter on the scan tool displays within the range of 0.7-2.8 volts or 8 kPa (1.16 psi) and 880 kPa (127.6 psi).

⇒ | If the parameter is not within the above range, replace the EOP sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Engine Oil Pressure Sensor and/or Switch Replacement

• | Control Module References for the ECM replacement, setup, and programming