P0088

DTC P0088

Description
The common rail fuel system is comprised of two fuel pressure sections: a suction side between the fuel tank and the fuel supply pump and a high-pressure side between the fuel supply pump and the fuel injectors. Fuel is drawn from the fuel tank via a feed pump and then pumped into the fuel rail by two plungers, all of which are internal to the fuel supply pump. This high pressure is regulated by the engine control module (ECM) using the fuel rail pressure (FRP) regulator dependant upon values from the FRP sensor attached to the fuel rail. In case of fuel rail overpressure, a pressure limiter valve threaded into the fuel rail will open to release overpressure and return fuel back to the fuel tank.

If the ECM detects that the fuel pressure went excessively high for a certain length of time, this DTC will set (First Stage). If the ECM detects that during the same ignition cycle the fuel pressure rose even higher than the amount to set DTC P0088 (Second Stage) for a certain length of time, the MIL will be illuminated. If the MIL is illuminated, the fuel pressure was too high and the pressure limiter valve did not active or did not activate quick enough.

Condition for Running the DTC
First Stage
- DTCs P0091, P0092, P0192, P0193, P0602, P0642 and P0643 are not set.
- The ignition switch is ON.

Second Stage
- DTCs P0091, P0092, P0192, P0193, P0602, P0642 and P0643 are not set.
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.

Condition for Setting the DTC
First stage
- The ECM detects that the fuel rail pressure is more than 26850 psi (185 MPa) for longer than 9 seconds.

Second Stage
- The ECM detects that the fuel rail pressure is momentarily more than 30200psi (208MPa) anytime during the ignition cycle after first stage has occurred. This indicates the fuel rail pressure is too high and pressure limiter valve most likely did not active.

Action Taken When the DTC Sets
First Stage
- The ECM will not illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.

Second Stage
- The ECM illuminate the MIL when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Freeze Frame/Failure Records.
- The ECM limits fuel rail pressure within 11600 psi (80 MPa).
- The ECM limits accelerator control range within 55%.
- The ECM closes the EGR valve and holds to close position.
- The ECM inhibits cruise control.
- The ECM inhibits PTO control.

Condition for Clearing the MIL/DTC
First Stage
- 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 non-emission related diagnostic.
- Clear the DTC with a scan tool.

Second Stage
- The ECM turns OFF the MIL after 3 consecutive driving cycles when the diagnostic runs and does not fail. (12,000 lbs GVW)
- The ECM turns OFF the MIL when the diagnostic runs and does not fail. (Except 12,000 lbs GVW)
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes after the key is cycled.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic after the ECM turns OFF the MIL.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
- An intermittently sticking fuel rail pressure (FRP) regulator may have allowed the fuel pressure to become high enough to set this DTC.
- Normal Actual Fuel Rail Pressure readings on the scan with the engine running in Park or Neutral at idle are around 3650 to 5050 psi (25 to 35 MPa) and around 14500 to 21750 psi (100 to 150 MPa) in Park or Neutral at W.O.T. (accelerator pedal full travel).
- A skewed FRP sensor value (shifted to a higher pressure) can set this DTC. The Actual Fuel Rail Pressure on the scan tool should read 0 psi (0 MPa) with the key ON and engine OFF after the engine has stopped running for a minimum of 2 minutes.
- Resistance in the FRP sensor low reference circuit can set this DTC. Ensure that the sensor low reference circuit has no resistance and the connectors are tight and free of corrosion.

NOTE: The Actual Fuel Rail Pressure on scan tool will only update with the engine running or one time after the key is cycled when the ignition has been turned OFF for longer than 10 seconds.

Test Description
The numbers below refer to the step number on the diagnostic table.
6. This step checks for a fuel restriction by determining if a high vacuum is being pulled on the fuel system during normal operation.
7. This step checks for an air leak on the suction side of the fuel system by determining if a vacuum can be pulled when a fuel line is plugged.
17. This DTC indicates that the fuel pressure went high and if the MIL was illuminated due to the second stage, then there is a possibility that the pressure limiter valve did not active.

DTC P0088
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Connector End Views or Engine Control Module (ECM) Connector End Views

Step 5:

Step 6 - 7:

Step 8 - 11:

Step 12 - 16:

Step 17 - 19: