Cummins fault code 379

What it means

Cummins' description: Fueling Actuator #1 Circuit - grounded circuit.

SPN 633 is Fueling Actuator #1 Circuit. FMI 6 means too much current is flowing in the circuit, usually a wire rubbed through to ground or a shorted component.

Modern Cummins engines build very high fuel pressure in a common rail that feeds the injectors. The ECM controls rail pressure with a fuel pump actuator and monitors it with a rail pressure sensor. A pressure relief valve protects the system.

What the lamp means

An amber (yellow) warning lamp means the engine can usually keep running, but the fault should be repaired soon, ideally the same day.

Common causes

FMI 6 is an electrical or signal fault, so start with the circuit:

• Rail pressure sensor or wiring fault
• Fuel pump actuator (metering valve) circuit fault
• Connector damage at the pump

If the circuit checks out, the reading may be real. Other possibilities: clogged fuel filters (the most common cause of low rail pressure); air in the fuel from a loose fitting or empty tank; weak lift pump or restricted fuel supply.

What you can check before calling

• Check when the fuel filters were last changed
• Make sure there's plenty of fuel in the tank
• Look for fuel leaks at the pump, rail and lines
• Notice hard starting, stalling or power loss under load

Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers.

Engines and sources

Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Diagnostic Fault Codes for Cummins Engines. Always confirm with Cummins service information (QuickServe) for your engine serial number.