Cummins fault code 434
Power Lost without Ignition Off: erratic or intermittent signal
What it means
Cummins' description: Power Lost without Ignition Off.
SPN 627 is Power Lost without Ignition Off. FMI 2 means the signal is jumping around, dropping in and out, or doesn't make sense compared to other readings.
The ECM needs clean, steady battery voltage, and it supplies regulated 5-volt power to many sensors. Voltage problems can cause strange codes across many systems at once.
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-voltage code after a hard winter start or after the truck sat a while, then clears.
Schedule a repair
Codes return, the truck is slow to crank, or voltage reads low while driving. Test the charging system soon.
Stop and get help
Engine dies, several systems drop out at once, or the ECM loses power. Don't run it until the power supply is fixed. It can leave you stranded.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Weak batteries
- Failing alternator
- Parasitic drain
What you can check before calling
- Check battery terminals and ground straps for corrosion or looseness
- Have the batteries and alternator tested
- Note if several unrelated codes appeared at the same time
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers. For the bigger picture, read our guide: Bad alternator or bad battery? How to tell.
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.
Related Battery, power supply and sensor supply codes
- 441 SPN 168 FMI 18
Battery 1 Voltage: reading below normal (moderately severe) - 442 SPN 168 FMI 16
Battery 1 Voltage: reading above normal (moderately severe) - 386 SPN 3509 FMI 3
Sensor Supply 1 Circuit: circuit voltage high / shorted high - 487 SPN 626 FMI 18
Start Enable Device 1 Canister Empty (Ether Injection): reading below normal (moderately severe) - 515 SPN 3514 FMI 3
Sensor Supply 6 Circuit: circuit voltage high / shorted high - 352 SPN 3509 FMI 4
Sensor Supply 1 Circuit: circuit voltage low / shorted low
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 434 mean?
Cummins fault code 434 is J1939 SPN 627 FMI 2: Power Lost without Ignition Off. In plain terms: power lost without ignition off: erratic or intermittent signal.
Can I keep driving with Cummins code 434?
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 434?
SPN 627 identifies the part or system (Power Lost without Ignition Off). FMI 2 describes the type of failure: erratic or intermittent signal.
What usually causes Cummins code 434?
The most common causes are: weak batteries; failing alternator; parasitic drain.
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.