Cummins fault code 394
Timing Actuator #1 Circuit: circuit open / current low
What it means
Cummins' description: Timing Actuator #1 Circuit - open circuit.
SPN 635 is Timing Actuator #1 Circuit. FMI 5 means the ECM is driving the circuit but almost no current flows, which usually means an open circuit: a broken wire, unplugged connector, or failed coil.
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.
Green, yellow, red: three ways this can look
The same code can be a quick fix or a reason to shut down. Match your situation to the closest example.
Keep an eye on it
A low rail pressure code right after a filter change or running the tank low, that clears once air is bled out.
Schedule a repair
Hard starts, hesitation, power loss, or the code keeps coming back. Change the fuel filters first, then have the pressure tested.
Stop and get help
Stalling, no-start, a red stop lamp, or fuel spraying anywhere. Shut it down. High-pressure fuel leaks are a fire and injury risk.
Common causes
FMI 5 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.
Same SPN, other failure types
- 112 SPN 635 FMI 7
Engine Timing Actuator is not responding to ECM commands: not responding / out of adjustment - 113 SPN 635 FMI 3
Engine Timing Actuator Circuit: circuit voltage high / shorted high - 114 SPN 635 FMI 4
Engine Timing Actuator Circuit: circuit voltage low / shorted low - 395 SPN 635 FMI 6
Timing Actuator #1 Circuit: circuit grounded / current high - 467 SPN 635 FMI 2
Timing Rail Actuator Circuit: erratic or intermittent signal
Related High-pressure fuel system codes
- 396 SPN 1244 FMI 5
Fueling Actuator #2 Circuit: circuit open / current low - 391 SPN 632 FMI 11
Fuel Shutoff Valve Supply Voltage error: root cause not known - 397 SPN 1244 FMI 6
Fueling Actuator #2 Circuit: circuit grounded / current high - 398 SPN 1245 FMI 5
Timing Actuator #2 Circuit: circuit open / current low - 399 SPN 1245 FMI 6
Timing Actuator #2 Circuit: circuit grounded / current high - 379 SPN 633 FMI 6
Fueling Actuator #1 Circuit: circuit grounded / current high
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does Cummins fault code 394 mean?
Cummins fault code 394 is J1939 SPN 635 FMI 5: Timing Actuator #1 Circuit - open circuit. In plain terms: timing actuator #1 circuit: circuit open / current low.
Can I keep driving with Cummins code 394?
Usually for a short time, if the engine runs normally and no other warnings are on. Get it diagnosed soon, because many amber codes lead to a derate if ignored. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 394?
SPN 635 identifies the part or system (Timing Actuator #1 Circuit). FMI 5 describes the type of failure: circuit open / current low.
What usually causes Cummins code 394?
The most common causes are: rail pressure sensor or wiring fault; fuel pump actuator (metering valve) circuit fault; connector damage at the pump.
Diesel down in the Midlands?
We work on Cummins-powered pickups, vans and medium-duty trucks across Lexington, Columbia and the Midlands, on site at your yard or roadside.