Cummins fault code 1938
ECU Power Output Supply Voltage 1: reading below normal (moderately severe)
What it means
Cummins' description: ECU Power Output Supply Voltage 1 - Data Valid But Below Normal Operating Range - Moderately Severe Level.
SPN 3597 is ECU Power Output Supply Voltage #1. FMI 18 means the value is clearly below normal operating range. It's the middle 'low' level.
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
Listed by Cummins for: QSB 6.7, QSL 9, QSX 15, QSB 4.5, 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.
Same SPN, other failure types
- 351 SPN 3597 FMI 12
Injector Power Supply: bad device or component - 1117 SPN 3597 FMI 2
Power Supply Lost With Ignition On: erratic or intermittent signal - 1939 SPN 3597 FMI 3
ECU Power Output Supply Voltage 1: circuit voltage high / shorted high - 1941 SPN 3597 FMI 4
ECU Power Output Supply Voltage 1: circuit voltage low / shorted low - 6499 SPN 3597 FMI 17
ECU Power Output Supply Voltage 1: reading below normal (least severe)
Related Battery, power supply and sensor supply codes
- 1777 SPN 2634 FMI 4
Power Relay Driver Circuit: circuit voltage low / shorted low - 1776 SPN 2634 FMI 3
Power Relay Driver Circuit: circuit voltage high / shorted high - 1696 SPN 3513 FMI 4
Sensor Supply 5: circuit voltage low / shorted low - 1695 SPN 3513 FMI 3
Sensor Supply 5: circuit voltage high / shorted high - 2185 SPN 3512 FMI 3
Sensor Supply 4 Circuit: circuit voltage high / shorted high - 2186 SPN 3512 FMI 4
Sensor Supply 4 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 1938 mean?
Cummins fault code 1938 is J1939 SPN 3597 FMI 18: ECU Power Output Supply Voltage 1 - Data Valid But Below Normal Operating Range - Moderately Severe Level. In plain terms: ecu power output supply voltage 1: reading below normal (moderately severe).
Can I keep driving with Cummins code 1938?
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 1938?
SPN 3597 identifies the part or system (ECU Power Output Supply Voltage #1). FMI 18 describes the type of failure: reading below normal (moderately severe).
What usually causes Cummins code 1938?
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.