Cummins fault code 779
Auxiliary Equipment Sensor Input # 3 (OEM Switch): root cause not known
What it means
Cummins' description: Auxiliary Equipment Sensor Input # 3 (OEM Switch).
SPN 703 is Auxiliary Equipment Sensor Input # 3 (OEM Switch). FMI 11 means the ECM detected a fault in this system but can't pin down the exact type. Further testing is needed.
These codes cover extra inputs and outputs the ECM controls or monitors: auxiliary temperature and pressure sensors, relays, lamps, and generator or equipment controls on off-highway and generator engines.
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
An auxiliary code for an accessory that isn't used on your truck.
Schedule a repair
An accessory, gauge or lamp not working with the code set. Fix the circuit when convenient.
Stop and get help
The code is tied to a shutdown or protection relay. Have it checked before relying on that protection.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Real reading from the equipment the input is monitoring
What you can check before calling
- Find out what the auxiliary input is wired to on your truck or equipment
- Check connectors and relays in that circuit
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 Auxiliary inputs, outputs and generator controls codes
- 528 SPN 93 FMI 2
Auxiliary Alternate Torque Validation Switch: erratic or intermittent signal - 527 SPN 702 FMI 3
Auxiliary Input/Output 2 Circuit: circuit voltage high / shorted high - 524 SPN 113 FMI 2
OEM Alternate Droop Switch Validation: erratic or intermittent signal - 444 SPN 620 FMI 18
OEM Sensor Supply Voltage Low: reading below normal (moderately severe) - 385 SPN 620 FMI 3
OEM Sensor Supply Voltage Circuit: circuit voltage high / shorted high - 339 SPN 1267 FMI 4
Idle Shutdown Vehicle Accessories Relay Driver 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 779 mean?
Cummins fault code 779 is J1939 SPN 703 FMI 11: Auxiliary Equipment Sensor Input # 3 (OEM Switch). In plain terms: auxiliary equipment sensor input # 3 (oem switch): root cause not known.
Can I keep driving with Cummins code 779?
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 779?
SPN 703 identifies the part or system (Auxiliary Equipment Sensor Input # 3 (OEM Switch)). FMI 11 describes the type of failure: root cause not known.
What usually causes Cummins code 779?
The most common causes are: real reading from the equipment the input is monitoring.
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.