Cummins fault code 423
Fuel Timing Pressure or Timing Actuator Stuck: erratic or intermittent signal
What it means
Cummins' description: Fuel Timing Pressure or Timing Actuator Stuck.
SPN 156 is Fuel Timing Pressure or Timing Actuator Stuck. FMI 2 means the signal is jumping around, dropping in and out, or doesn't make sense compared to other readings.
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
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
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
Related High-pressure fuel system codes
- 399 SPN 1245 FMI 6
Timing Actuator #2 Circuit: circuit grounded / current high - 398 SPN 1245 FMI 5
Timing Actuator #2 Circuit: circuit open / current low - 397 SPN 1244 FMI 6
Fueling Actuator #2 Circuit: circuit grounded / current high - 449 SPN 157 FMI 0
Injector Metering Rail 1 Pressure: reading above normal (most severe) - 396 SPN 1244 FMI 5
Fueling Actuator #2 Circuit: circuit open / current low - 395 SPN 635 FMI 6
Timing 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 423 mean?
Cummins fault code 423 is J1939 SPN 156 FMI 2: Fuel Timing Pressure or Timing Actuator Stuck. In plain terms: fuel timing pressure or timing actuator stuck: erratic or intermittent signal.
Can I keep driving with Cummins code 423?
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 423?
SPN 156 identifies the part or system (Fuel Timing Pressure or Timing Actuator Stuck). FMI 2 describes the type of failure: erratic or intermittent signal.
What usually causes Cummins code 423?
The most common causes are: 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.
Diesel down in the Midlands?
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