Technical Description of OBD-II Trouble Code
The O2 Sensor Reference Voltage Circuit for Bank 2 Sensor 1 is Too Low
What is the meaning of P2249?
P2249 is a generic powertrain code that applies to many OBD-II vehicles (1996-newer). This includes vehicles from various manufacturers such as Honda, Ford, Mazda, VW, Mercedes-Benz, Audi, Hyundai, Acura, BMW, etc. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P2249 indicates that the powertrain control module (PCM) has detected a low reference voltage for the upstream O2 sensor for engine bank two. Sensor 1 refers to an upstream sensor, and Bank 2 refers to the bank of the engine that does not contain the number one cylinder.
The PCM monitors the engine air to fuel ratio for each engine bank using data input from heated exhaust oxygen sensors. These oxygen sensors have a zirconium dioxide sensing element located in the center of a vented steel housing. The sensing element is connected to wire leads in the oxygen sensor harness connector, which plugs into the controller area network (CAN) that connects to the PCM connector.
Each oxygen sensor is threaded or studded into an exhaust pipe, positioned near the center of the pipe. As exhaust gases flow over the oxygen sensors, they enter through vent holes in the steel housing and swirl around the sensing element. Ambient air is drawn through wire lead cavities in the sensor housing, filling a tiny chamber in the middle. The air in this chamber is heated, causing the oxygen ions to produce voltage that is recognized by the PCM.
Variations in the number of oxygen ions in the ambient air drawn into the O2 sensor, compared to the number of oxygen molecules in the exhaust, cause the oxygen ions inside the sensor to rapidly bounce between platinum layers. These variations in oxygen sensor output voltage indicate changes in exhaust oxygen concentration. The voltage signal from the oxygen sensors is lower when there is more oxygen in the exhaust (lean condition) and higher when there is less oxygen in the exhaust (rich condition).
If the PCM detects a low electrical value in the oxygen sensor reference voltage, it will store a code P2249 and may illuminate the malfunction indicator lamp (MIL). In most cases, the MIL will only illuminate after multiple ignition cycles with a failure.
A typical oxygen O2 sensor:
What is the severity of this DTC?
An insufficient voltage in the O2 sensor reference voltage circuit can lead to reduced fuel efficiency and engine performance. A code P2249 should be considered severe and addressed as soon as possible.
What are some of the symptoms of the code?
Symptoms of a P2249 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P2249 troubleshooting steps?
To accurately diagnose a code P2249, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.
It may save time to search for technical service bulletins (TSB) that match the stored code, vehicle information (year, make, model, and engine), and exhibited symptoms. This information can usually be found in your vehicle information source. If a relevant TSB is found, it may provide a quick solution to the diagnosis.
After connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data, write down the information in case the code is intermittent. Then, clear the codes and test drive the vehicle until one of two things happens: the code is restored or the PCM enters readiness mode.
If the PCM enters readiness mode at this point, the code may be more difficult to diagnose because it is intermittent. The condition that caused the P2249 code to be stored may need to worsen before an accurate diagnosis can be made. If the code is restored, continue with the diagnosis.
You can obtain connector face views, connector pinout charts, component locator charts, wiring diagrams, and diagnostic flow charts specific to the code and vehicle in question from your source of vehicle information.
Perform a visual inspection of the related wiring and connectors. Repair or replace any wiring that is cut, burned, or damaged.
Use the DVOM to test the O2 sensor voltage at the appropriate connector pin near the sensor. If no voltage is detected, check the system fuses and replace any blown or defective fuses as needed.
If voltage is detected, test the corresponding circuit at the PCM connector. If no voltage is detected there, suspect an open circuit between the sensor and the PCM. If voltage is discovered at the PCM connector, suspect a defective PCM or PCM programming error.
To test the O2 sensors: Start the engine and allow it to reach normal operating temperature. Let the engine idle (with the transmission in neutral or park). With the scanner connected to the vehicle diagnostic port, observe the oxygen sensor input data on the data stream. Narrow down the data stream to include only relevant data for a faster response.
If the oxygen sensors are functioning normally, the voltage on the pre-oxygen sensors will continuously cycle between 1 and 900 millivolts once the PCM enters closed loop operation. The post sensors will also cycle between 1 and 900 millivolts, but they will settle at a certain point and remain relatively stable compared to the pre sensors. If the oxygen sensors fail to cycle adequately and the engine is in good working order, they should be considered defective.
