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 Descriptors

DTC P0090: Fuel Pressure Regulator Control Circuit
DTC P0091: Fuel Pressure Regulator Solenoid 1 Control Circuit Low Voltage
DTC P0092: Fuel Pressure Regulator Solenoid 1 Control Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
FRP regulator High | P0091 | P0090 | -- | --
FRP regulator Low | P0091 | P0090 | P0092 | --

### Circuit/System Description

High pressure fuel is regulated by the fuel rail pressure (FRP) regulator, which is a part of the high pressure fuel pump. The FRP regulator is a solenoid valve. The ECM provides battery voltage on the FRP regulator high circuit and ground on the FRP regulator low circuit. Both circuits are controlled through output drivers within the ECM. When deactivated, both drivers are disabled. When activated, the FRP regulator low circuit driver connects the low circuit to ground and the FRP regulator high circuit driver pulse-width modulates (PWM) the high circuit. The ECM monitors the voltage on the circuits to detect a failure.

### Conditions for Running the DTC

• | DTC P0641, P0642, or P0643 is not set.

• | The ignition voltage is between 6-18 volts.

• | DTCs P0090, P0091, and P0092 run continuously.

### Conditions for Setting the DTC

#### P0090

• | The fuel pressure regulator voltage is between 2.7-4.5 volts with the fuel pressure regulator commanded OFF.

• | The above condition is present for greater than 3 second.

#### P0091

• | The fuel pressure regulator voltage is less than 2.7 volts with the fuel pressure regulator commanded OFF.

• | The above condition is present for greater than 3 second.

#### P0092

• | The fuel pressure regulator voltage is greater than 4.5 volts with the fuel pressure regulator commanded ON.

• | The above condition is present for greater than 3 second.

### Action Taken When the DTC Sets

• | DTCs P0090, P0091, and P0092 are Type A DTCs.

• | A message center or an indicator displays Reduced Engine Power.

### Conditions for Clearing the DTC

DTCs P0090, P0091, and P0092 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. Engine idling, observe the Actual Fuel Rail Pressure parameter with a scan tool. The pressure should be approximately 3.5-5.5 Mpa (508-798 psi).
2. Command an increase and decrease in fuel rail pressure with a scan tool. Observe the scan tool Actual Fuel Rail Pressure parameter. The Actual Fuel Rail Pressure should increase or decrease with each command.
3. 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, raise the vehicle.
2. Disconnect the harness connector at the high pressure fuel pump.
3. Engine running, verify that a test lamp flashes between the FRP regulator low circuit terminal 1 and B+.

⇒ | If the test lamp is always ON, test the FRP regulator low circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒ | If the test lamp is always OFF, test the FRP regulator low circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Ignition ON, verify that a test lamp illuminates between the FRP regulator high circuit terminal 2 and ground.

⇒ | If the test lamp does not illuminate, test the FRP regulator high circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the high pressure fuel pump.

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the harness connector at the high pressure fuel pump.

Note: The DMM and test leads must be calibrated to 0 Ω in order to prevent misdiagnosis.

2. Test for 0.49 Ω ±0.023 Ω at 20°C (68°F) between FRP regulator low circuit terminal 1 and FRP regulator hi circuit terminal 2.

⇒ | If not within the specified range, replace the high pressure fuel pump.

3. Test for infinite resistance between each terminal and the high pressure fuel pump housing.

⇒ | If not the specified value, replace the high pressure fuel pump.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Pump Replacement

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