Cummins fault code7979 · DC/DC 2 Operational Status
DC/DC 2 Operational Status - Voltage Above Normal or Shorted to High Source
7979 Cummins fault code as shown in INSITE / CaltermSPN8895 · DC/DC 2 Operational StatusFMI3 Voltage above normal, or shorted to high sourceOBD codenone (J1939 only)LampAmber WARNING lampCummins textDC/DC 2 Operational Status - Voltage Above Normal or Shorted to High SourceFailure modeVoltage Above Normal or Shorted to High SourceWhat Cummins code 7979 means
The signal wire for DC/DC 2 Operational Status is sitting above the voltage window the ECM expects. In practice that is usually an open signal or return wire (the ECM pull-up takes the input high), a short to the 5 V supply or battery, or a failed sensor element.
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 8895 FMI 3 rather than as Cummins code 7979. 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 8895 DC/DC 2 Operational Status
4 other fault codes share this SPN; each one is a different failure mode (FMI) of the same component.
Related Cummins fault codes
J1939 failure mode identifiers (FMI)
FMI 3 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 7979
What does Cummins fault code 7979 mean?
Cummins 7979 is "DC/DC 2 Operational Status - Voltage Above Normal or Shorted to High Source". It maps to SPN 8895 FMI 3. The signal wire for DC/DC 2 Operational Status is sitting above the voltage window the ECM expects. In practice that is usually an open signal or return wire (the ECM pull-up takes the input high), a short to the 5 V supply or battery, or a failed sensor
Which lamp does fault code 7979 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 7979?
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 7979 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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