Cummins Fault Code 779

Circuit Description

The original equipment manufacturer (OEM) has the option of wiring a pressure or temperature sensor input to the Cummins engine control module (ECM). A specific calibration is then created to recognize this pressure or temperature sensor input. This fault code is activated when the pressure or temperature input from the OEM sensor exceeds the engine protection limit defined by the OEM. Depending on OEM requirements, an Engine Protection derate can be associated with this fault code.

Component Location

The OEM pressure sensor input and location will vary. Refer to the OEM service manual for sensor location.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes

The Engine Control Module (ECM) detected the engine protection limit for the OEM input device was exceeded.

Action Taken When the Fault Code is Active

The regulated derate conditions may vary depending on the OEM and local regulations.

Conditions for Clearing the Fault Code

• To validate the repair, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• The “Reset All Faults” command in the recommended Cummins electronic service tool or equivalent can be used to clear active and inactive faults.

Shop Talk

This fault code is activated when the pressure or temperature input from the OEM sensor exceeds the engine protection limit defined by the OEM. An engine power derate is possible, depending on the OEM application.