Cummins ISB CM850 (2003-06) Fault Code: 449 (ISC – Auto) PID: 94 SPN: 157 FMI: 0 Injector Metering Rail Number 1 Pressure – Data Valid But Above Normal Operating Range – Most Severe Level. Fuel pressure signal indicates that fuel pressure has exceeded the maximum limit for the given engine rating.

Cummins ISB CM850 (2003-06) Fault Code: 449 (ISC – Auto) PID: 94 SPN: 157 FMI: 0 Injector Metering Rail Number 1 Pressure – Data Valid But Above Normal Operating Range – Most Severe Level. Fuel pressure signal indicates that fuel pressure has exceeded the maximum limit for the given engine rating.

Fault Code 449 is activated when the sensed rail fuel pressure exceeds the opening pressure of the rail fuel pressure relief valve.

In normal engine operation the ECM calibration varies the flow command to the fuel pump actuator to achieve the correct fuel rail pressure. System failures that cause loss of pressure control can cause the fuel rail pressure relief valve to open. The fuel rail pressure relief valve acts to protect the high pressure components from over-pressurization. If the ECM detects that the fuel rail pressure relief valve is open without a detection of a fuel pump actuator circuit error, Fault Code 449 will become active.

On certain applications, the ECM will try to reset automatically causing a momentary loss of power for less than one second.

Conditions that can cause Fault Code 449:

1)Purging air through the fuel system can cause a pressure overshoot, therefore causing Fault Code 449 to log.
2)Sustained periods of very low pressure under load followed by pressure recovery overshoot. This can be caused by high restriction due to plugged filters.
3)A tampered fuel pressure sensor that reads low, a biased pressure sensor, or a poor electrical connection.
4)If an intermittent electrical circuit problem, of the fuel pump actuator circuit, exists it is possible for Fault Code 449 to become active then inactive during normal engine operation. ECM Fault Code 2311 is designed to detect electrical circuit issues with the actuator. Therefore, it is only necessary to look for bad connectors or harness issues for Fault Code 449 if no other fault codes exist.
5)Other conditions include faulty ECM wiring harness such as poor grounds, battery voltage spikes, electrical noise, low alternator output, and large disturbances of battery voltage, as when jump starting the vehicle.

Possible repairs:

1)Replace the pressure side fuel filter.
2)Replace the gear pump.
3)Clean or replace the ECM cooling plate.
4)Clean or replace the check valve.
5)Replace the rail fuel pressure sensor.
6)Replace the fuel pump actuator o-rings.
7)Replace the fuel pump actuator.