Some Cummins engine fault codes include 111, which indicates an internal engine control unit failure; 214, which indicates that the engine's oil temperature is too high; and 434, which indicates that power was lost while the ignition was off. There are several hundred other Cummins engine diagnostic fault codes. A full list of diagnostic fault codes is obtainable for each Cummins engine in the owner's manual or from several online resources.
Cummins engines use fault codes to let operators know that the system is not functioning properly. When a fault code has been activated, the operator is alerted to the condition through an audible or visual alarm. In most cases, the activation of a fault code illuminates a fault limit. If the fault is severe in nature, the engine may reduce its operating speed to prevent further damage. On vehicles equipped with the Cummins RoadRelay system, the operator receives an audible alarm indicating that a fault has occurred.
Several different types of fault lamps alert the operator to the severity of the specific fault code. A blue lamp indicates that it is time for a maintenance action to be performed. A yellow warning lamp means that a failure has occurred, but the vehicle can continue to operate. A red stop lamp indicates that a critical failure has occurred, requiring that the engine be shut down as soon as possible. If the red stop lamp is blinking, this means that a critical failure has occurred and that the engine has begun a 30-second emergency shutdown procedure to prevent further damage.
Cummins engines use the SAE J1939 standard to report fault codes. This standard requires that each fault code be transmitted from the engine control to a user interface via a unique FMI and SPN code.