COVER 3949528 - Caterpillar

for the NRS Pressure Sensors for Plugging
Remove the steel tubing, the mounting block, the NRS differential pressure sensor, and the absolute pressure sensor.
Check the steel tubing for a buildup of exhaust soot. If necessary, use compressed air to check the steel lines for plugging. If a buildup of soot is found in the tubing, you may expect further buildup in the mounting block for the sensors.
Inspect the passages in the mounting block for the sensors for a buildup of exhaust soot. Also, inspect the differential pressure sensor and the absolute pressure sensor for plugging due to an accumulation of exhaust soot. Results:
OK - Little or no soot buildup is evident.Repair: The absolute pressure sensor and the differential pressure sensor for the NRS are not reading the pressure correctly. Replace the differential pressure sensor and the absolute pressure sensor.Clear all diagnostic codes. Use Cat ET to perform an "EGR Service Test" in order to verify that the problem is resolved.STOP
Not OK - Soot buildup is evident in the components of the NRS differential pressure sensors.Repair: Remove the NRS venturi. Clean the following components:
Passages of the NRS venturi
Steel tubing
Mounting block for the sensors
Differential pressure sensor
Absolute pressure sensorReplace parts, if necessary.Clear all diagnostic codes. Use Cat ET to perform an "EGR Service Test" in order to verify that the problem is resolved.STOPTest Step 10. Use Cat ET to Check for Active Codes
Establish a connection between the engine ECM and Cat ET.
Check for diagnostic codes that are active or logged. Check for codes that became active during the "EGR Service Test". Check for the following codes:
3386-3 Engine Exhaust Gas Recirculation Temperature Sensor : Voltage Above Normal
3386-4 Engine Exhaust Gas Recirculation Temperature Sensor : Voltage Below NormalExpected Result:No codes are generated during the test.Results:
OK - No codes are generated. Proceed to Test Step 11.
Active 3386-3 or 3386-4 - A code related to the NRS temperature sensor became active during the "EGR Service Test".Repair: There is an electrical problem in the circuit for the NRS temperature sensor. There may be a problem with the sensor. Refer to Troubleshooting, "Sensor Signal (Analog, Passive) - Test" for information that is related to troubleshooting the problem.STOPTest Step 11. Inspect the NRS Valve
Remove the actuator assembly from the NRS valve body. Use the appropriate screwdriver to rotate the valve inside the NRS valve body. The valve should freely rotate from Open to Closed for 90 degrees of rotation. Results:
NRS valve does not rotate at all, or the valve is difficult to rotate. - Repair: Replace the NRS valve body. Install the actuator assembly that was previously removed.Clear all diagnostic codes and use Cat ET to perform an "EGR Service Test" in order to verify that the problem is resolved.STOP
The NRS valve does rotate freely through all 90 degrees of rotation. - Repair: Install a new actuator assembly.Clear all diagnostic codes and use Cat ET to perform an "EGR Service Test" in order to verify that the problem is resolved.STOPTest Step 12. Create an Open Circuit at the Harness