SPN 94 FMI 1 — Fuel rail pressure too low

SPN 94 identifies the parameter the control module is monitoring — fuel rail pressure too low. FMI 1 is the failure mode the module logged against it. Both numbers matter: the same SPN with a different FMI is a different repair.

Rough running, hard start, power loss under load.

• Plugged fuel filters
• Failing high pressure fuel pump
• Air leak on the suction side

• Change both fuel filters
• Check for air in the clear fuel line
• Perform a rail pressure leak-down test

Work the list in order and record the readings. Confirm the fault with live data before any part is ordered — a code names a circuit, never a failed component.

Short distance only

It may get you home but it can also die on the shoulder. Only run it if home is close and you can pull off safely.

• Replacing the sensor named in the SPN before checking its wiring, connector and ground.
• Clearing the code and handing the truck back without reproducing the operating condition that set it.
• Reading one code out of a set instead of finding which fault occurred first.

Get a shop involved when the fault comes with a red lamp or a shutdown timer, when the checks above all pass and the code returns, or when the repair needs an aftertreatment service tool, a forced regen, or engine internals. Nothing on this page is a substitute for OEM service literature or a qualified technician on the truck.

Enter this code in Blue Collar AI diagnostic support with the engine and the symptoms and you get the test sequence in order, per-truck history so repeat faults are visible, and a printable work order. Aftertreatment codes are covered in depth in the Aftertreatment Mastermind training. It is all in Truck Commander at $14.99 a month.