Circuit DescriptionThe fuel pump contains two barrel and plunger assemblies; each barrel and plunger assembly utilizes an intake and outlet check valve. Fuel at gear pump pressure is metered through the fuel pump actuator and unseats one of the two intake check valves as the fuel at gear pump pressure enters the pumping chamber. As the pumping plunger begins its upward motion, the pressure in the pumping chamber increases rapidly and the intake check valve is closed. As pressure reaches accumulator pressure, the outlet check valve is opened. As the plunger travels upward, fuel exits past the outlet check valve and pressurizes the fuel rail.

Component LocationThe fuel pump is located on the back side of the gear housing. The barrel and plunger and check valve assemblies are part of the fuel pump head sub-assembly.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the engine is operating.

Conditions for Setting the Fault CodesThis fault code is set active when a pumping imbalance is detected between the high-pressure plungers inside the fuel pump.

Action Taken When the Fault Code is ActiveThe engine control module (ECM) illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.Conditions for Clearing the Fault CodeTo validate the repair using a Diagnostic Road Test, utilize a route that incorporates both stop-and-go city driving and steady state highway driving. It may be necessary to load the unit for certain diagnostics in the ECM to run.To validate the repair using a Chassis Dynamometer Test, utilize a routine that incorporates acceleration and motoring events, steady state highway operation, and load. This will simulate normal driving and allow the diagnostics in the ECM to run.The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the ECM detects that the pumping imbalance has been corrected and the diagnostic runs and passes.The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults.

Shop TalkFault Code 281 will most likely come active while operating at a steady state loaded condition. At this condition, commanded fuel pressures are highest and the pump’s pressure balance is affected the most.

If a high pressure seal has a malfunction, pump head drain flow will be excessive. If a seal malfunction has progressed far enough, the engine may not start because of an inability to develop fuel rail pressure.

If the engine will not start, there are two indications that the pump head has failed (refer to the appropriate service manual for more information):

The drain flow will be excessive. This can be measured while cranking the engine.The pumping plungers are broken or mechanically stuck. This can be checked by visual inspection.If the engine oil level is rising and Fault Code 281 is active, the pump head has a malfunction and must be replaced.

Possible Cause:1) Fuel Gear Pump module failure2) High Pressure fuel pump head failure3) ECM calibration