BOSS 4V0679 - Caterpillar

Probable Causes
Diagnostic codes
Coolant temperature sensor circuit
Low coolant temperature
Glow plugs
Fuel quality
Valve lash
Low compression (cylinder pressure)
Individual malfunctioning cylinderRecommended Actions
Diagnostic Codes
Use one of the following methods to check for active diagnostic codes:
The electronic service tool
The display on the control panelElectronic Service Tool
Connect the electronic service tool to the diagnostic connector.
Check for active diagnostic codes on the electronic service tool.
Investigate any active codes before continuing with this procedure. Refer to Troubleshooting, "Troubleshooting with a Diagnostic Code".Display on the Control PanelNote: The following procedure is only applicable if the application is equipped with a display on the control panel.
Check the display on the control panel for active diagnostic codes.
Troubleshoot any active codes before continuing with this procedure. Refer to Troubleshooting, "Troubleshooting with a Diagnostic Code".Coolant Temperature Sensor Circuit
Connect the electronic service tool to the diagnostic connector.
Monitor the display screen on the electronic service tool in order to verify the presence of active diagnostic codes for the coolant temperature. Refer to Troubleshooting, "Engine Temperature Sensor Open or Short Circuit - Test".
If the fault has not been eliminated, proceed to "Low Coolant Temperature".Low Coolant Temperature
Check that the water temperature regulator is operating correctly. Refer to Systems Operation, Testing, and Adjusting, "Water Temperature Regulator - Test".If the water temperature regulator is operating correctly, proceed to "Glow Plugs".Glow Plugs
Check for correct operation of the glow plugs. Refer to Troubleshooting, "Glow Plug Starting Aid - Test".
If necessary, replace faulty glow plugs. Refer to Disassembly and Assembly, "Glow Plug - Remove and Install".
If the repairs do not eliminate the fault, proceed to "Fuel Quality".Fuel Quality
Check the diesel fuel for quality. Refer to Systems Operation, Testing, and Adjusting, "Fuel Quality - Test".Note: Diesel fuel with a low cetane value is likely to cause white smoke.
If the repair does not eliminate the fault, proceed to "Valve Lash".Valve Lash
Ensure that the valve lash is correct. Refer to Systems Operation, Testing, and Adjusting, "Engine Valve Lash - Inspect".
If the repair does not eliminate the fault, proceed to "Low Compression (cylinder pressure)".Low Compression (cylinder pressure)
Perform a compression test. Refer to Systems Operation, Testing, and Adjusting, "Compression - Test ".
If low compression is noted on any cylinders, investigate the cause and rectify the cause.Possible causes of low compression are shown in the following list:
Loose glow plugs
Faulty piston
Faulty piston rings
Worn cylinder bores
Worn valves
Faulty cylinder head gasket
Damaged cylinder head
Perform all necessary repairs.
Ensure that the repair has eliminated the fault.
If the repair does not eliminate the fault, proceed to "Individual Malfunctioning Cylinder".Individual Malfunctioning Cylinder
With the engine speed at a fast idle, use the electronic service tool to perform the manual "Cylinder Cut Out Test". As each cylinder is cut out, listen for a change in the sound from the engine. When a cylinder is cut out, there should be a noticeable change in the sound of the engine. If a change in the sound of the engine is not noted, the isolated cylinder is not operating under normal conditions. If the isolation of a cylinder causes a change in the sound that is less noticeable, the cylinder may