SEAL 4Y0371 - Caterpillar

Probable Causes
NOx Reduction System (NRS) cooler leak
Aftertreatment Regeneration Device (ARD) head leaking coolant (If equipped)
Cylinder head gasket leak
Cylinder head leakRecommended Actions
Table 1
Troubleshooting Test Steps Values Results
1. NRS cooler
A. Check the NRS cooler for leaks utilizing the "On Engine Test Procedure". Refer to Testing and Adjusting, "Exhaust Cooler (NRS) - Test".
NRS Cooler
Result : The NRS cooler has a leak.
Repair: Replace the NRS cooler. Refer to the Disassembly and Assembly manual for the correct procedure.
Result : The NRS cooler does not have a leak.
Proceed to Test Step 2.
2. Check the ARD head (if equipped)
A. Pressurize the cooling system. Refer to Systems Operation/Testing and Adjusting, "Cooling System - Test" for the correct procedure.
B. Remove the ARD head. Refer to the Disassembly and Assembly manual for the correct procedure.
C. Inspect the combustion can for signs of coolant leaking from the ARD nozzle heater o-ring seals.
Coolant Leak
Result : The ARD head is leaking coolant.
Repair: Replace the ARD head. Refer to the Disassembly and Assembly manuals for the correct procedure.
Result : The ARD head is not leaking coolant.
Proceed to Test Step 3.
3. Cylinder head gasket leak
A. Check the cylinder head gasket for leaks. Refer to the Systems Operation/Testing and Adjusting manual for the proper procedure for checking the cylinder head.
Cylinder Head Gasket
Result : The cylinder head gasket is leaking.
Repair: Replace the cylinder head gasket. Refer to the Disassembly and Assembly manual.
Result : The cylinder head gasket is not leaking.
Proceed to Test Step 4.
4. Cylinder head
A. Check for cracks in the cylinder head. Perform a leak test on the cylinder head. Refer to Systems Operation/Testing and Adjusting for the proper procedure for checking the cylinder head.
Cylinder Head
Result : A crack is found in the cylinder head.
Repair: Repair the cylinder head and/or replace the cylinder head. Refer to the Disassembly and Assembly manual. If the procedure did not correct the issue, contact your Dealer Technical Communicator (TC). For further assistance, the TC can confer with the Dealer Solutions Network (DSN).