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 P0251 00: Fuel Pressure Regulator Control Circuit Malfunction
DTC P0252 54: Fuel Pressure Regulator Performance
DTC P0253 00: Fuel Pressure Regulator Control Circuit Low Voltage
DTC P0254 00: Fuel Pressure Regulator Control Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition | P0253 00 | P0251 00 | -- | P0252 54
Control | P0253 00 | P0251 00 | P0254 00 | P0252 54

### Circuit/System Description

The fuel pressure regulator is used to control the fuel pressure at the high pressure pump. The fuel pressure regulator is pulse width modulated (PWM). The engine control module (ECM) supplies the voltage directly to the fuel pressure regulator. The ECM controls the solenoid by grounding the control circuit with a solid state device called a driver.

### Conditions for Running the DTC

• | The ignition is ON, or the engine is running.

• | The ignition voltage is less than 16 V.

• | The DTCs runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0251

The ECM detects the Fuel Pressure Regulator Control Circuit is open for more than 1 s.

#### P0252 54

The ECM detects an overtemperature at the output control driver of the fuel pressure regulator.

#### P0253

The ECM detects the fuel pressure regulator control dircuit is shorted to ground for more than 1 s.

#### P0254

The ECM detects the fuel pressure regulator control circuit is shorted to voltage for more than 1 s.

### Action Taken When the DTC Sets

DTC P0251, P0252 54, P0253 and P0254 are type A DTCs.

### Conditions for Clearing the DTC

DTC P0251, P0252 54, P0253 and P0254 are type A DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Fuel System Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTCs P0251, P0252 54, P0253 orP0254 should not set.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the Q18 Fuel Pressure Regulator.
2. Ignition ON, verify a test lamp illuminates between the ignition voltage circuit terminal 1 and ground.

⇒ | If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the K20 Engine Control Module (ECM).

3. Ignition ON, test the voltage between the control circuit terminal 2 and ground. The voltage should be within 3-4 V.

⇒ | If less than the specified range, test the control circuit for an open or a short to ground. If circuit tests normal, replace the K20 Engine Control Module (ECM).

⇒ | If greater than the specified range, test the control circuit for a short to voltage. If circuit tests normal, replace the K20 Engine Control Module (ECM).

4. Test for less than 5 Ω on the ignition voltage circuit, and the control circuit.

⇒ | If greater than the specified range, repair the appropriate circuit for a high resistance.

5. If all circuits test normal, test or replace the Q18 Fuel Pressure Regulator.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the Q18 Fuel Pressure Regulator.
2. Test for 4-6 Ω between the control terminal 2 and the ignition voltage terminal 1.

⇒ | If not within the specified range, replace the Q18 Fuel Pressure Regulator.

3. Test for infinite resistance between each terminal and the solenoid Q18 Fuel Pressure Regulator housing.

⇒ | If not the specified value, replace the Q18 Fuel Pressure Regulator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | LINK

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