Technical Description of OBD-II Trouble Code
Bank 2 NOx Sensor Heater Sense Circuit
What does that signify?
This is a standard diagnostic trouble code (DTC) that applies to OBD-II vehicles. It can be found in various vehicle makes such as Mercedes-Benz, Sprinter, VW, Audi, Ford, Dodge, Ram, Jeep, etc.
NOx (Oxides of Nitrogen) sensors are primarily used in diesel engines for emission systems. They detect the levels of NOx in the exhaust after combustion in the engine’s chamber. The system then recycles these emissions using different methods. Due to the harsh environment, these sensors are made of a combination of ceramic and a specific type of zirconia.
One of the negative impacts of emitting NOx into the atmosphere is the potential for smog and acid rain. Failing to monitor and adjust NOx levels properly can have a significant effect on the air we breathe and the environment. The Engine Control Module (ECM) continuously monitors the NOx sensors to ensure acceptable emission levels in the vehicle’s exhaust.
The ECM calculates the levels of Nitric Oxide and Nitrogen Dioxide gases (NOx) by using data from the upstream and downstream oxygen sensors, along with the NOx sensor readings. This is done to regulate the NOx levels emitted from the tailpipe for environmental reasons. The trouble code refers to Bank 2, which is the engine bank that does not contain the #1 cylinder.
P2221 is the identified trouble code for “NOx Sensor Heater Sense Circuit Bank 2.” This is a general fault detected by the ECM on bank #2, most likely due to an abnormal NOx reading.
It is important to note that diesel engines produce a significant amount of heat, so it is crucial to allow the system to cool before working on any exhaust system components.
Here is an example of a NOx sensor for GM vehicles:
What is the severity of this DTC?
If the trouble codes are ignored and no action is taken to repair them, it could lead to catalytic converter failure. Neglecting the symptoms and causes of these trouble codes can result in further complications for the car, such as consistent stalling and reduced fuel economy. If you notice any of the potential symptoms listed below, it is highly recommended to have your vehicle checked by a professional.
What are some of the symptoms of the code?
Symptoms of a P2221 diagnostic code may include:
What are some of the common causes of the code?
Possible causes for the P2221 NOx sensor code may include:
What are some P2221 diagnostic and troubleshooting steps?
The first step in troubleshooting any malfunction is to research the Technical Service Bulletins (TSB) for known issues with your specific vehicle.
Advanced diagnostic steps may vary depending on the vehicle and may require specialized equipment and knowledge. The basic steps provided below should be supplemented with a vehicle-specific repair guide for accurate steps.
Basic Step #1
Always start by clearing the codes and rescanning the vehicle. If none of the DTCs (Diagnostic Trouble Code) become active immediately, take the vehicle for a lengthy multi-stop test drive to see if they reappear. If only one of the codes is reactivated by the ECM, continue the diagnostic process for that specific code.
Basic Step #2
Next, check the exhaust system for any leaks. Black soot around cracks and gaskets indicates a leak. Address this issue accordingly, as replacing an exhaust gasket is usually a straightforward task. A fully sealed exhaust system is crucial for the proper functioning of the sensors involved.
Basic Step #3
Use an infrared temperature gun to monitor the temperature of the exhaust before and after the catalytic converter. Compare the results to the manufacturer’s specifications, referring to the specific service manual for guidance.
Basic Step #4
If the catalytic converter temperature is within the specified range, focus on the electrical system related to these sensors. Start with the harness and connector of the bank 2 NOx sensor. These harnesses often crack and fail due to the extreme temperatures near the exhaust. Repair any damaged wires by soldering the connections and using heat shrink tubing. Also, inspect the oxygen sensors involved in bank 2 to ensure they are not damaged, as this can affect the downstream NOx readings. Repair any connectors that are not making sufficient connections or not locking properly.
This article is intended for informational purposes only, and the technical data and service bulletins specific to your vehicle should always take precedence.
