P1094
DTC P1094Description
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 suction control valve (SCV) dependant upon values from the fuel rail pressure (FRP) sensor attached to the fuel rail.
If the ECM detects that the fuel pressure after an injection event dropped quickly compared with injection before, this DTC will set. This most likely indicates some loss of fuel pressure or intermittently loss of fuel pressure by fuel leak from the high pressure side.
Condition for Running the DTC
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.
- The engine speed is higher than 650 RPM.
Condition for Setting the DTC
- The ECM detects that the fuel rail pressure was normal, then sharply decreased.
Action Taken When the DTC Sets
- The ECM illuminates 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.
- The ECM limits accelerator control rage at idle.
- The ECM limits fuel rail pressure less than 11600 psi (80 MPa).
- 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 DTC
- A current DTC clears when the ignition is turned OFF.
- Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
- An intermittently sticking suction control valve (SCV) may have allowed the fuel pressure to drop suddenly.
- 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).
- An intermittently sticking fuel injector may have allowed the fuel pressure to drop too much. Use a scan tool to perform the Cylinder Power Balance test for each injector. Verify a consistent engine speed change when commanding each fuel injector ON and OFF.
- A skewed fuel rail pressure (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:
- This DTC most likely indicates loss fuel pressure by fuel leak from the high pressure side. Inspect the high pressure side fuel leakage between the fuel supply pump and fuel injector FIRST.
- 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.
- The fuel system from the fuel tank(s) to the fuel supply pump is under a slight vacuum with the engine running. As a result, air can enter the fuel system if these connections are not tight or if there is a crack in one of the fuel hoses. Air in the fuel system will cause fuel rail pressure fluctuations especially at high engine speed and load, which may set this DTC.
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.
DTC P1094
Schematic Reference: Engine Controls Schematics
Step 4 - 6:
Step 7 - 9:
Step 10 - 14:
Step 15 - 20:
