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 P0087: Fuel Rail Pressure (FRP) Too Low
DTC P0088: Fuel Rail Pressure (FRP) Too High
DTC P0089: Fuel Pressure Regulator Performance

### Circuit/System Description

The fuel rail pressure sensor detects fuel pressure within the fuel rail. The engine control module (ECM) provides a 5-volt reference voltage on the 5-volt reference circuit and ground on the low reference circuit. The ECM receives a varying signal voltage on the signal circuit.

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 a 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 ECMs high circuit driver energizes the FRP regulator and the low circuit driver pulse-width modulates (PWM) the low circuit to ground.

The high pressure mechanical fuel pump is driven by three lobes on the camshaft. The ECM uses the camshaft and crankshaft position sensor inputs to synchronize the FRP regulator with the position of each of the camshaft lobes. The ECM regulates fuel pressure by adjusting the portion of each pump stroke that provides fuel to the rail.

The ECM monitors the fuel pressure sensor and the FRP regulator to determine if the commanded and actual pressure are within a predetermined range, or if the amount of fuel pressure correction exceeds a calibrated pressure.

### Conditions for Running the DTC

• | DTC P0090, P0091, P0092, P0191, P0192, or P0193 is not set.

• | The ignition voltage is less than 18 volts.

• | The deceleration fuel cut-off (DFCO) is inactive.

• | The engine speed is greater than 25 RPM.

• | The air bag is not deployed.

• | DTCs P0087, P0088, and P0089 run continuously when the above conditions are met for 5 seconds.

### Conditions for Setting the DTC

#### P0087

The actual fuel rail pressure is 1,500 kPa (218 psi) less than the desired fuel pressure. The condition exists for greater than 5 seconds.

#### P0088

The actual fuel rail pressure is 3,600 kPa (522 psi) greater than the desired fuel rail pressure. The condition exists for greater than 5 seconds.

#### P0089

The fuel rail pressure regulator command necessary to maintain the desired fuel rail pressure is +/-2,500 kPa (363 psi) of the command expected by the controller. The condition exists for greater than 5 seconds.

### Action Taken When the DTC Sets

• | DTCs P0087, P0088, and P0089 are Type A DTCs.

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

### Conditions for Clearing the DTC

DTCs P0087, P0088, and P0089 are Type A DTCs.

### Diagnostic Aids

• | A skewed fuel rail pressure (FRP) sensor, or an intermittent condition in the FRP sensor circuits will set these DTCs.

• | Leaking or restricted fuel injectors may set DTC P0089.

### 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. Observe the DTC information with a scan tool. DTC P029D, P02A1, P02A5, P02A9, P02AD, P02B1, P0627, P0628, P0629, P069E, or U0109 should not set.

⇒ | If a DTC is set refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Attempt to start and idle the engine.
3. Observe the DTC information with a scan tool. DTCs P0087, P0088, and P0089 should not set.
4. 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).
5. 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 commanded state.
6. 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

Note: Circuit/System Verification must be performed first or misdiagnosis may result.

1. Test the fuel system for 345-414 kPa (50-60 psi). Refer to Fuel Pressure Gage Installation and Removal.

⇒ | If the fuel pressure is not within the specified range, refer to Fuel System Diagnosis.

Note: As little as 2 Ω of resistance on either circuit of fuel pressure regulator (FRP) solenoid will cause these DTCs to set. Test the circuits of the FRP solenoid for a high resistance if you suspect a condition.

2. Remove the high pressure fuel pump assembly and visually inspect the lobes on the camshaft for unusual wear.

⇒ | If the lobes appear normal, replace the high pressure fuel pump assembly.

⇒ | If the lobes are worn, replace the camshaft.

### 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 ohms in order to prevent misdiagnosis.

2. Test for 0.49 Ω plus/minus 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. Measure the resistance between each terminal and the high pressure fuel pump housing. The DMM should display OL Ω.

⇒ | If less than the specified value, replace the high pressure fuel pump.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Camshaft Removal - Left Side

• | Fuel Pump Replacement