TROUBLESHOOTING SHACK

Blaming the NOx sensor for any code that contains the term “NOx” in its description is a common occurrence. While it is true that a simple NOx sensor replacement often resolves most NOx-related codes, there are instances where this solution proves ineffective. This guide aims to shed light on potential issues that may arise.

*Important Note-Before starting the diagnosis process, verify that the ECM calibration is up to date. An outdated ECM calibration can lead to issues with sensors and modules.

This comprehensive guide pertains to codes 3232 and 2772, regardless of whether they are active simultaneously or separately:

Fault code: 3232 SPN: 3216 Aftertreatment 1 Intake NOx Sensor-Abnormal Update Rate

Fault code: 2771 SPN: 3226 Aftertreatment 1 Outlet NOx Sensor-Abnormal Update Rate

Prior to commencing the diagnosis of any aftertreatment codes, it is crucial to diligently check for additional active codes that may require resolution before proceeding with any aftertreatment procedures. In particular, pay close attention to codes related to the EGR, Turbo, or CAN Lines (also known as J1939 Data Link, Communication Circuit). Neglecting this preliminary step may significantly impact the overall health and performance of the aftertreatment system, as its functionality heavily relies on the engine’s condition.

Subsequently, we highly recommend exploring relevant Technical Service Bulletins that may apply to the engine. Manufacturers consistently release these types of bulletins, which often prove to be invaluable resources.

Additionally, it is advisable to verify that the ECM calibration remains up to date. As the truck ages and newer parts are installed, an outdated calibration can lead to misinterpretation of potential issues.

Continuing the evaluation process, it is imperative to meticulously inspect the battery system, a crucial component that is sometimes overlooked. In the case of multiple battery systems, individual testing of each battery and a thorough examination of all grounding connections are essential.

At this juncture, focus your attention on the NOx sensor itself. Performing a basic connector and pin check can help identify potential issues such as water intrusion or corrosion, which are common culprits behind NOx sensor malfunctions. If the connector appears unaffected, proceed to conduct a circuit test. Given that the NOx sensor relies on battery voltage, ensure that the appropriate voltage is consistently supplied. Additionally, carefully examine for shorts to ground.

If no issues have been detected thus far, the next step involves assessing the J1939 Data Link. Begin by scrutinizing the 120-ohm resistors. Unplug the resistor and test for 60 ohms on the two data link pins. Deviation from this value may indicate potential problems with the harness or the VGT (Variable Geometry Turbo) actuator, which will be thoroughly evaluated in the subsequent step.

Continuing the evaluation, proceed to test the VGT by disconnecting it and measuring the resistance of the J1939 data link (+) and (-) on the VGT actuator connector on the harness side. Ideally, the resistance should measure 120 ohms. If not, the VGT may be the source of the problem. Conversely, if the VGT test yields satisfactory results, reconnect and continue with the evaluation.

Moving forward with the J1939 data link assessment, carefully inspect the harness on the OEM side. Disconnect the OEM harness at the crossover point and proceed to test the J1939 data link (+) and (-) for 120 ohms. Any deviation from the expected reading may indicate issues with one of the data link wires in the harness. In such cases, the next step is to verify the ohms on the individual data link wires on the harness, with an anticipated reading of 10 ohms.

By adhering to these systematic procedures, a comprehensive diagnosis of the NOx-related codes can be conducted, leading to accurate and effective solutions.