Cummins fault code 3727

What it means

Cummins' description: High Pressure Common Rail Fuel Pressure Relief Valve - Mechanical system not responding or out of adjustment.

SPN 5571 is High Pressure Common Rail Fuel Pressure Relief Valve. FMI 7 means the ECM commanded something to move or change and it didn't respond the way it should: sticking, binding, worn, or out of adjustment.

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

This code normally doesn't turn on a dash lamp. It's logged in the ECM for a technician to see, and often explains another active code.

Common causes

The sensor reading itself is out of range or the condition is real, so look at the system:

• 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
• Worn high-pressure pump
• Injector leaking back too much fuel
• Pressure relief valve opening or leaking

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

Listed by Cummins for: QSB 6.7, QSL 9, QSX 15, QSB 4.5, QSF 3.8, QSG 12. 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: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.