C7.1 Engines Caterpillar

Clean Emissions Module Has High Oxygen Level

Usage:

C7.1 881

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Table 1
Diagnostic Trouble Codes for CEM High Oxygen Level
J1939 Code	CDL Code	Code Description (code descriptions may vary)	Comments
3217-16	E1407 (2)	Aftertreatment #1 Intake O2 : High - moderate severity (2)	The engine out NOx Sensor is reading high O²
3227-16	E1408 (2)	Aftertreatment #1 Outlet O2 : High - moderate severity (2)	The tailpipe out NOx Sensor is reading high O²
Follow the troubleshooting procedure in order to identify the root cause of the fault.

The engine out NOx sensor is located in the CEM. The tailpipe out NOx sensor is located in the exhaust tail pipe. Refer to Illustration 1.

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Illustration 1	g03752556
Typical NOx sensor locations (1) Engine out NOx sensor (2) Exhaust tailpipe (typical example) (3) Tailpipe out NOx sensor

The exhaust system has two NOx sensors that measure O2 and NOx. The engine out NOx sensor is located in the CEM. This sensor monitors the NOx and O2 exiting the DPF. The tailpipe out NOx sensor is located in the exhaust tail pipe after the SCR catalyst and monitors the NOx and O2 exiting the CEM.

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Check the Installation of the NOx Sensors A. Locate the appropriate NOx Sensor. B. Check if the sensor is installed correctly.	Correctly Installed / Not installed correctly	Result: The sensor is not installed correctly. Repair: Install the sensor correctly. Proceed to Test Step 3. Result: The sensor is installed correctly. Proceed to Test Step 2.
2. Check for an Exhaust Leak Between the Turbocharger and the Tailpipe A. Check for disconnected exhaust lines. B. Check for broken/loose joints.	Leak found	Result: An exhaust leak is found between the turbo and the tail pipe. Repair: Repair the exhaust leak. Proceed to Test Step 3.
3. Perform the Aftertreatment System Functional Test A. Reset all active codes and clear all logged codes. B. Use the electronic service tool to perform the "Aftertreatment System Functional Test" in order to verify that the fault is eliminated.	Test passed	Result: The Aftertreatment System Functional Test passed. The NOx Sensing system is fully functional and the fault has been eliminated. Return the unit to service. Result: The Aftertreatment System Functional Test did not pass and the diagnostic code is still present. Repair: Replace the sensor. If the fault is still present, contact the Dealer Solutions Network (DSN).