Cummins fault code7991 · DC/DC 2 SLI Battery Terminal Voltage
DC/DC 2 SLI Battery Terminal Voltage - Bad Intelligent Device or Component
7991 Cummins fault code as shown in INSITE / CaltermSPN8915 · DC/DC 2 SLI Battery Terminal VoltageFMI12 Bad intelligent device or componentOBD codenone (J1939 only)LampAmber WARNING lampCummins textDC/DC 2 SLI Battery Terminal Voltage - Bad Intelligent Device or ComponentFailure modeBad Intelligent Device or ComponentWhat Cummins code 7991 means
A smart device or component involved with DC/DC 2 SLI Battery Terminal Voltage has failed its own internal test or is returning data the ECM considers invalid. For ECM internal faults the usual outcome is an ECM replacement or re-flash; for external smart sensors it is normally the sensor.
It lights the amber CHECK ENGINE (warning) lamp. The engine keeps running, but a torque or speed derate may apply depending on the calibration and on how long the fault stays active.
On a generic J1939 scan tool, or on the dash of a Freightliner, Kenworth, Peterbilt, International or Volvo chassis, the same fault is shown as SPN 8915 FMI 12 rather than as Cummins code 7991. Cummins INSITE and Calterm show the Cummins number, the SPN / FMI pair and the lamp together.
Custom DTC delete, up to 30 codes, $150. Full DPF / EGR / SCR delete with all related codes and derates, $500. Upload your Calterm .xcal, tick the services, pay with PayPal, and the finished file comes back by email and WhatsApp.
Upload your .xcal →Cummins ECFG / E2M definitions for CM550, CM552, CM554, CM570, CM800, CM850, CM870, CM871 and more: the fault table, torque, fuelling, boost, EGR, DPF and SCR maps, ready for Calterm or WinOLS. Instant download.
Find your ECFG →Other Cummins codes on SPN 8915 DC/DC 2 SLI Battery Terminal Voltage
Code 7991 is the only Cummins fault code assigned to SPN 8915.
Related Cummins fault codes
J1939 failure mode identifiers (FMI)
FMI 12 is highlighted. The FMI is the second half of every J1939 fault and tells you how the component failed; the SPN tells you which component.
| FMI | Meaning (SAE J1939-73) |
|---|---|
| 0 | Data valid but above normal operational range - most severe level |
| 1 | Data valid but below normal operational range - most severe level |
| 2 | Data erratic, intermittent or incorrect |
| 3 | Voltage above normal, or shorted to high source |
| 4 | Voltage below normal, or shorted to low source |
| 5 | Current below normal or open circuit |
| 6 | Current above normal or grounded circuit |
| 7 | Mechanical system not responding or out of adjustment |
| 8 | Abnormal frequency, pulse width or period |
| 9 | Abnormal update rate |
| 10 | Abnormal rate of change |
| 11 | Root cause not known |
| 12 | Bad intelligent device or component |
| 13 | Out of calibration |
| 14 | Special instructions |
| 15 | Data valid but above normal operating range - least severe level |
| 16 | Data valid but above normal operating range - moderately severe level |
| 17 | Data valid but below normal operating range - least severe level |
| 18 | Data valid but below normal operating range - moderately severe level |
| 19 | Received network data in error |
| 20 | Data drifted high |
| 21 | Data drifted low |
| 22 | Reserved for SAE assignment |
| 23 | Reserved for SAE assignment |
| 24 | Reserved for SAE assignment |
| 25 | Reserved for SAE assignment |
| 26 | Reserved for SAE assignment |
| 27 | Reserved for SAE assignment |
| 28 | Reserved for SAE assignment |
| 29 | Reserved for SAE assignment |
| 30 | Reserved for SAE assignment |
| 31 | Condition exists |
Questions about code 7991
What does Cummins fault code 7991 mean?
Cummins 7991 is "DC/DC 2 SLI Battery Terminal Voltage - Bad Intelligent Device or Component". It maps to SPN 8915 FMI 12. A smart device or component involved with DC/DC 2 SLI Battery Terminal Voltage has failed its own internal test or is returning data the ECM considers invalid. For ECM internal faults the usual outcome is an ECM replacement or re-flash; for external smart
Which lamp does fault code 7991 turn on?
Amber WARNING lamp: It lights the amber CHECK ENGINE (warning) lamp. The engine keeps running, but a torque or speed derate may apply depending on the calibration and on how long the fault stays active.
How do I clear or permanently delete Cummins code 7991?
An active code goes inactive on its own once the condition is gone; the inactive record stays in the ECM fault history until it is cleared with Cummins INSITE (or a J1939 tool that supports the DM3 / DM11 clear). If the code keeps coming back because the part is gone, disconnected or not worth repairing, the lasting fix is to disable fault 7991 in the calibration: upload your .xcal to the ECFG Superstore file service, custom DTC delete from $150 (up to 30 codes), full DPF / EGR / SCR delete $500, and flash the returned file with Calterm or INSITE.
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