CM850 Electronic Control System – FAULT CODE 559 (ISB/QSB Automotive, Marine or Industrial Application)

Fuel Pump Delivery Pressure Low – Data Valid but Below Normal Operational Range – Moderately Severe Level


Fault Code: 559
PID: P157
SPN: 157
FMI: 1/18
LAMP: Amber

Fuel Pump Delivery Pressure Low – Data Valid but Below Normal Operational Range – Moderately Severe Level. The ECM has detected that fuel pressure is lower than commanded pressure.

Possibly hard to start, low power, or engine smoke. Engine can possibly not start.

Fuel Flow Diagram

Circuit Description

The fuel pressure control loop relies on fuel pressure supplied to the high-pressure pump by the electric lift pump and low-pressure pump. The ECM monitors rail fuel pressure and engine operating conditions and changes the flow command to maintain the proper rail fuel pressure. Changes to the flow command result in opening (or closing) of the electronic fuel control actuator to supply more (or less) fuel to the high-pressure pump.

The fuel flow circuit includes, in the following order of fuel flow:

  • Fuel tank
  • OEM fuel supply line
  • OEM 300-micron filter
  • ECM cooling plate
  • Electric lift pump
  • Fuel filter
  • Gear pump
  • Electronic fuel control actuator
  • High-pressure fuel pump
  • Rail fuel (includes fuel pressure relief dump valve and pressure sensor)
  • High-pressure fuel lines
  • High-pressure fuel connectors
  • Injectors
  • Return to tank.

Component Location

The fuel pump is located at the rear of the engine, on the intake side of the engine. Use the foolowing procedure for a detailed component location view. Refer to Procedure 100-002 in Section E.

Shop Talk

Causes of this fault code include the following:

  • High inlet restriction
  • Excessive air in fuel
  • Loss of fuel prime during cranking
  • Plugged fuel filter
  • Low lift pump pressure
  • Stuck or restricted electronic fuel control actuator
  • System return (excessive return flow from the injector, high-pressure pump, or rail pressure relief valve)
  • Tampering.

If the drain line is restricted completely, the high pressure fuel pump will be damaged, causing internal leakage. Prior to pump damage, fault codes indicative of a drain line restriction will occur. Following the damage, these fault codes will go inactive and Fault Code 559, which is indicative of leakage, will be active. If troubleshooting Fault Code 559 results in replacement of the pump and there are inactive counts of Fault Codes 553 or 449, the fuel drain line must be inspected and the fuel drain line restriction measured. This is to reduce the possibility of repeat high pressure pump damage.

Refer to Troubleshooting Fault Code t05-559b

Last Modified:  15-Sep-2010