CONE-BEARING 6V8795 - Caterpillar

Use this procedure to troubleshoot excessive Selective Catalytic Reduction (SCR) catalyst sulfation. Also, use this procedure if the following event code is active or logged.
Table 1
J1939 Code and Description Comments
4792-14
Aftertreatment #1 SCR System : Special Instruction Sulfation of the Selective Catalytic Reduction (SCR) catalyst has exceeded an acceptable level.
The code status is active. Over time, sulfur from the diesel fuel builds up on the Selective Catalytic Reduction (SCR) catalyst. When sulfation becomes excessive the catalyst loses the ability to convert NOx, resulting in higher emissions.The sulfur deposited on the catalyst can be removed by operating the engine at high exhaust temperatures for an extended period.The engine must be operated so the SCR intake gas temperature exceeds one of the following:
425° C (797° F) for a minimum duration of 90 minutes.
450° C (842° F) for a minimum duration of 30 minutes.Note: The required temperature threshold must be exceeded for the minimum duration or the desulfation process will be voided.If the desulfation process is voided, the next time the temperature threshold is exceeded the duration timer will start from zero.When the temperature requirement is maintained for the minimum duration, the desulfation process is completed and the active code will be removed.Probable Causes
Codes
TemperatureRecommended Actions
Table 2
Troubleshooting Test Steps Values Results
1. Check for Codes
A. Connect Cat® Electronic Technician (ET) to the service tool connector.
B. Look for active codes that are associated with the system for the event code.
Codes
Result: An associated code is active.
Repair: Troubleshoot any associated codes before continuing with this test.
Result: A code is active.
Proceed to Test Step 2.
2. Elevate the Engine Exhaust Temperature by Applying the Normal Load
A. Start the engine.
B. Run the engine to run until normal operating temperature is reached.
C. If possible, apply load to the engine.
D. Connect Cat ET.
E. Use Cat ET to monitor the following parameter:
- "SCR Inlet Temperature"
Target Temperature
425° C (797° F)
450° C (842° F)
Result: The target temperature was exceeded.
Proceed to Test Step 4.
Result: The target temperature was not exceeded.
Proceed to Test Step 3.
3. Elevate the Engine Exhaust Temperature by Blocking the ATAAC
A. Gradually block off the ATAAC.
B. Connect Cat ET.
C. Use Cat ET to monitor the following parameters:
- "SCR Inlet Temperature"
- "Air Intake Manifold Temperature"
- "Engine Coolant Temperature"
Note: Watch for alarms. Do not exceed the parameters upper limit for the engine application.
Target Temperature
425° C (797° F)
450° C (842° F)
Result: The target temperature was exceeded.
Proceed to Test Step 4.
Result: The target temperature was not exceeded.
Contact your TC for assistance.
4. Continue Operating the Engine Under the Current Conditions
A. Continue to exceed the target temperature for the minimum duration.
B. Connect Cat ET.
C. Use Cat ET to monitor the following parameter:
- "SCR Inlet Temperature"
Target Temperature and Duration
450° C (842° F) for a minimum duration of 30 minutes.
425° C (797° F) for a minimum duration of 90 minutes.
Result: The code changed from an active status to a logged status after the minimum duration for the temperature.
The Selective Catalytic Reduction (SCR) catalyst is now OK. Return to service.
If the procedure did not correct the issue, contact your Cat dealer Technical Communicator