Driver Technique

The ISM engine is equipped with an diagnostic system. It is one of the most powerful parts of the engine package. As the engine is operated, this diagnostic system monitors operation information from electronic devices that are installed throughout the vehicle. The diagnostic system uses this information to determine the cause of engine failures.

When a failure occurs, the diagnostic system stores a fault code and may light an operator fault lamp depending on the situation. In some severe cases, the engine will actually limit speed or power output to reduce the chance of progressive damage. The fault codes are used by service technicians to troubleshoot and identify engine failure modes. The fault lamps tell the operator how to react to the engine failure.

Should the vehicle be equipped with a Cummins RoadRelay 4 the operator will be alerted to a system fault through an audible alarm. In addition, RoadRelay will also provide important details concerning the fault including: the fault code, a short description of the fault, current status, (Active or Inactive), recommended driver response and the number of times the fault has been experienced.

Fault Lamps
The operator fault lamps are the interface between the driver and the engine. The color and sequence of fault lamps designate that a certain action should take place. In some severe cases fault lamps are accompanied by engine de-rates or actual engine shutdown.


  • Blue (Maintenance) Lamp: An illuminated blue (maintenance) lamp means that the engine requires maintenance or fluids. The vehicle should be serviced as soon as possible to correct the problem. If ignored, some maintenance conditions can cause improper engine operation and even progressive damage.


  • Yellow (Warning) Lamp: An illuminated yellow (warning) lamp means that a failure has occurred, but the vehicle can be operated without progressive damage. The vehicle should be serviced as soon as possible to diagnose the failure.


  • Red (Stop) Lamp: An illuminated red (stop) lamp means that a major failure has occurred that can result in progressive damage or affect safe operation of the vehicle. The vehicle should be shutdown as soon as safely possible.
    Flashing Red (Stop) Lamp: A flashing red (stop) lamp means that the engine control system has started the shutdown sequence. The shutdown timer will give the operator 30 seconds to find a safe stopping point.

Limp Home
Some failure modes cause the engine to perform so poorly that the vehicle is disabled. Several of these failure modes are recognized by the electronic control system and a backup operating mode is enabled. This mode is called Limp Home. Limp Home is recognized by a yellow fault lamp and an obvious reduction in engine performance. The operator should report Limp Home modes immediately and take the vehicle to the closest repair location available. Limp Home is only designed to avoid stranding the vehicle in an inconvenient location. It should not be used for extended periods of engine operation.

Fault Codes
Fault code information can be flashed out with the operator interface lamps, read directly from the RoadRelay in-cab display or downloaded using an authorized Cummins' software tool such as INSITE.

You must use the diagnostic switch installed in the vehicle cab to flash out fault codes with the operator fault lamps. To check for active engine fault codes and maintenance indicator codes, turn the keyswitch to the OFF position and move the diagnostic switch to the ON position. Now turn the keyswitch to the ON position. If no active fault codes are recorded, both the warning and stop lamps will illuminate and remain on. If active faults are recorded, both the warning and stop lamps will illuminate momentarily and then begin to flash the codes of the recorded faults.

The fault code will flash in the following sequence:

  • A yellow warning lamp will flash

  • There will be a short 1 - 2 second pause

  • The fault code will flash on the red stop lamp

  • There will be a short 1 - 2 second pause between each number

When the number has finished flashing in red, a yellow warning lamp will appear again. The fault code will repeat the sequence.

Each fault code will flash twice before advancing to the next code.