853722 15 Mercury NUT

Probable Causes
Inlet system leak
Engine operating conditions
Failed exhaust back pressure valve
High altitude
Obstructed Air-to-Air Aftercooler (ATAAC)
Illustration 1 g03795585
Example of an electronic service tool screenshot of the histogram. This histogram is populated when the engine system has calculated a condition in which high exhaust temperatures are present. A diagnostic code will not be logged when the system calculates a high exhaust temperature condition. The engine will be derated in order to protect the engine system. This situation is normal under most circumstances and no additional troubleshooting is necessary.
Note: Information from this histogram is to be used with active and logged diagnostic trouble codes. This histogram is for information only.Complete the procedure in the order in which the steps are listed.
Table 1
Troubleshooting Test Steps Values Results
1. Check for Inlet System Leakage
A. Apply a light load to the engine and check for leakage from the inlet system downstream of the low-pressure turbocharger.
Boost leaks
Result: Leakage was found.
Repair: Repair the leaks. Return the unit to service.
Result: Leakage was not found.
Proceed to Test Step 2.
2. Check the Engine Operating Conditions
A. Use the electronic service tool to check the histograms. Use the histograms to determine if the high exhaust temperature was due to normal operation.
If possible, interview the operator. Determine if the engine is being operated under heavy load. Ensure that the engine is being operated at an acceptable engine speed.
If derates are suspected, reset the histogram and return the unit to service. If the histogram repopulates without fault codes, the derating of the engine was under normal engine operation.
Normal operation
Result: The code was logged during a heavy load.
Repair: Reduce the load on the engine. Return the unit to service.
Result: The code was not logged during a heavy load.
Proceed to Test Step 3.
3. Check the Exhaust Back Pressure Regulator (EBPR)
A. Check the EBPR for correct operation. Refer to Troubleshooting, "Motorized Valve - Test" for the correct troubleshooting procedure.
Note: An EBPR that has failed in the closed position can cause high exhaust temperatures.
Failed exhaust back pressure regulator
Result: The exhaust back pressure regulator has failed.
Repair: Repair or replace the valve. Return the unit to service.
Result: The exhaust back pressure regulator has not failed.
Proceed to Test Step 4.
4. Check the Engine Operating Altitude
A. Check the engine operating altitude.
Note: High altitudes can cause high exhaust temperatures, consider the operational altitude when troubleshooting a high exhaust temperature. High exhaust temperatures are associated with high operational altitudes.
When operating below 5500ft and the ambient temperature is below 30° C (85° F), altitude should not cause a high exhaust temperature derate.
High operational altitudes
Result: The engine was operating at high altitudes.
The high exhaust temperature was due to high altitudes. Return the unit to service.
Result: The engine was not operating at high altitudes.
Proceed to Test Step 5.
5. Check for an Obstructed Air-to-Air Aftercooler (ATAAC)
A. The intake manifold air temperature can increase if the flow through the ATAAC is obstructed. Check the ATAAC for obstructions or debris. Ensure that the flow of air or coolant through the ATAAC is adequate.
Obstructed aftercooler
Result: The engine ATAAC was obstructed.
Repair: Clear any obstructions. Return the unit to service.
If the procedure did not correct the issue, contact the Dealer Solutions Network (DSN).