C175 Oil&Gas Offshore Engine Caterpillar

Use this procedure to troubleshoot a high oxygen level in the Clean Emissions Module (CEM). Also, use this procedure if one of the following event codes is active or logged.

Table 1

J1939 Code and Description	CDL Code and Description	Comments
3217-16 Aftertreatment #1 Intake O2 : Low - least severe (1)	E1407(2) High Aftertreatment #1 Intake O2 Concentration	The NOx sensors are detecting a higher than normal oxygen concentration.
3227-16 Aftertreatment #1 Outlet O2 : Low - least severe (1)	E1408(2) High Aftertreatment #1 Outlet O2 Concentration	The NOx sensors are detecting a higher than normal oxygen concentration.

The engine out NOx sensor is located on the mixer assembly between the turbocharger outlets and the inlet to the CEM.

The tailpipe out NOx sensor is located on the outlet of the CEM.

Probable Causes

• Sensor

• Leaks

• Codes

Recommended Actions

Table 2

Troubleshooting Test Steps	Values	Results
1. Verify that the NOx Sensors are Installed A. Locate the appropriate NOx Sensor. B. Check if the sensor is installed properly.	Sensor	Result: The sensor is not installed properly. Repair: Install the sensor properly. Proceed to Test Step 4. Result: The sensor is installed properly. Proceed to Test Step 2.
2. Check for Exhaust Leaks A. Start the engine. B. Check the exhaust system for proper installation. C. Check for loose or broken exhaust joints. D. Inspect the exhaust system between the turbocharger outlet and the tailpipe outlet for signs of an exhaust leak.	Leaks	Result: An exhaust leak was not found. Proceed to Test Step 3. Result: An exhaust leak was found. Repair: Repair or replace damaged exhaust component. If the problem is not resolved, proceed to Test Step 3.
3. Replace the NOx Sensor A. Remove electrical power from the engine. B. Replace the failed NOx sensor.	Sensor	Result: The NOx sensor was replaced. Proceed to Test Step 4.
4. Operate the Engine A. Apply electrical power to the engine. B. Start the engine. C. Run the engine until normal operating temperature is reached. D. Connect Cat® Electronic Technician (ET) to the service tool connector. E. Use Cat ET to monitor the following: - Codes	Codes	Result: A code is not active. Return to service.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).