P0088

DTC P0088

DTC DESCRIPTORS

DTC P0087
Fuel Rail Pressure (FRP) Too Low

DTC P0088
Fuel Rail Pressure (FRP) Too High

DIAGNOSTIC FAULT INFORMATION






IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

CIRCUIT/SYSTEM DESCRIPTION
The fuel injection pump supplies high pressure fuel to the fuel injection rails, and then to the fuel injectors through high pressure pipes. The fuel rail pressure (FRP) sensor is a three wire sensor mounted in the right fuel injection rail. The FRP sensor uses a 5-volt reference circuit , a signal circuit, and a low reference circuit to monitor fuel rail pressure. This information is sent to the engine control module (ECM) to assist in the fueling of the engine.

CONDITIONS FOR RUNNING THE DTC

P0087
- DTCs P0090, P0192, P0193 are not set.
- The engine is running.

P0088
- DTCs P0087, P0192, P0193 are not set.
- The engine is running.

CONDITIONS FOR SETTING THE DTC

P0087
- The actual FRP is more than 15 MPa (2,176 psi) below the desired FRP.OR
- The actual FRP is less than 22.5 MPa (3,263 psi).

P0088
- The actual FRP is more than 20 MPa (2,900 psi) above the desired FRP.OR
- The actual FRP is more than 1,89 MPa (27,412 psi)

ACTION TAKEN WHEN THE DTC SETS
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. The control module records the operating conditions at the time the diagnostic fails and stores this information in the Freeze Frame/Failure Records. The ECM will limit fuel injection.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS

P0087
- When ambient temperatures are below 0°C (32°F), the fuel tank pickup screen may be iced over from water in the fuel tank.
- When power enhancing devices have been attached to the fuel rail pressure sensor circuits, this DTC may set and adversely effect the fuel system components.
- When the fuel heater is on all the time, the fuel temperature may stay high enough to thin the fuel and cause this DTC to set.

P0088
- Driveability concerns may not occur with this DTC present.
- If the fuel system pressure is actually too high, a fuel knock and smoke condition will exist.
- A sticking FRP regulator may cause this DTC to set.

SPECIAL TOOLS REQUIRED
J 44638 Vacuum Gage

CIRCUIT/SYSTEM VERIFICATION
With engine running, observe the Actual Fuel Rail Pressure parameter with a scan tool. A normal reading would be approximately 40 MPa (5,802 psi)with the engine cold, and 30 MPa (4,351 psi) at operating temperature. Inspect the fuel supply lines for damage between the fuel tank and the fuel injection pump.

CIRCUIT/SYSTEM TESTING

IMPORTANT: Fuel pressure control will be disabled if DTC P0087, P0088, P0912, or P0193 are set. Codes must be cleared to enable the device control.

P0087
1. If DTC P0090, P0168 or P0191 is also set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
2. Attempt to start the engine.

IMPORTANT: Ensure that the transmission is in Park or Neutral with the parking brake set.
- If the engine does not start, refer to Engine Cranks but Does Not Run.
3. Install the J 44638 to the fuel rail service port and slowly increase the engine speed until reaching wide open throttle (WOT).
- If more than 5 inches of vacuum was present during engine speed increase, replace the fuel filter and inspect for fuel system restrictions.
4. Command the fuel pressure control to 180 MPa (23,206 psi) with a scan tool. Observe the Actual Fuel Rail Pressure parameter. The actual fuel pressure should be the same as the commanded pressure.
- If the Actual Fuel Rail Pressure is less than 145 MPa (21,030 psi), refer to Fuel System Diagnosis - High Pressure Side.
5. Operate the vehicle within the conditions for which the customer complaint occurs while observing the J 44638. You may also operate the vehicle within the conditions that you observed in the Freeze Frame/Failure Records.

IMPORTANT: If the fuel temperature is near 121°C (250°F) during the duplication of the complaint, or in the Failure Records for this DTC, inspect for a restriction in the fuel cooler air flow or the fuel heater always ON. Refer to Fuel Heater Always On.

- If the vacuum was more than 12 inches Hg of vacuum at any time in the operating range, inspect for a restriction in the fuel supply lines.
- If the vacuum was always less than 12 inches Hg of vacuum, refer to Diagnostic Aids.

P0088
1. Start the engine and operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
2. Observe the Actual Fuel Pressure parameter with a scan tool. The actual pressure should be 30 MPa (4,352 psi) with the engine idling at operating temperature.
3. Change the fuel pressure with a scan tool, incrementing through the entire fuel pressure range. The fuel pressure should increment and stabilize through the entire fuel pressure range, with actual and desired fuel pressure within 2 MPa (290 psi) of each other.
- If the pressure difference between the actual and desired pressure are more than 2 MPa (290 psi), replace the fuel pressure regulator.
4. Test the fuel pressure regulator (FPR) solenoid control circuit and the FPR solenoid supply voltage circuit for high resistance.
- If all circuits test normal, replace the ECM.


REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Control Module References for ECM replacement, programing and setup
- Fuel Rail Pressure (FRP) Sensor Replacement
- Fuel Pressure Regulator Replacement