Technical Description of OBD-II Trouble Code
Bank 2 is experiencing a post catalyst fuel trim system that is too rich.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured in 1996 or later (Ford, Dodge, GMC, Chevrolet, Mercedes, VW, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
When I encounter a trouble code P2099, I know that it means the powertrain control module (PCM) has detected a signal voltage input from the downstream (post catalyst) oxygen (O2) sensor for engine bank one that indicates the oxygen particle content is too low. Bank 2 refers to the engine bank that does not contain the #1 cylinder.
The O2 sensor consists of a zirconium dioxide sensing element enclosed within a vented steel housing. Platinum electrodes are used to connect the sensing element to wire leads in the O2 sensor wiring harness. The O2 sensor wiring harness is connected to the PCM via the controller area network. The O2 sensor provides real-time data to the PCM regarding the percentage of oxygen particles in the engine exhaust compared to the oxygen content of ambient air.
Exhaust gases from the engine pass through the exhaust manifold, into the exhaust pipe, and through the catalytic converter. Afterward, they pass over the downstream O2 sensor. The exhaust gases flow through vent holes in the steel housing and across the sensing element. Outside air is drawn into a chamber in the middle of the sensor, through the wire lead cavities. In the chamber, ambient air is heated, causing the oxygen ions to produce voltage. Fluctuations in voltage occur as the oxygen ions move between platinum layers. The PCM recognizes these voltage changes as variations in exhaust oxygen concentration, which indicate whether the engine is running lean (too little fuel) or rich (too much fuel). The voltage signal output from the O2 sensor is lower when more oxygen is present in the exhaust (lean condition) and higher when less oxygen is present (rich condition). The PCM uses this data to calculate fuel delivery strategy and ignition timing, among other things.
Once the PCM enters closed loop operation, if the readings from the bank 2 downstream O2 sensor circuit indicate too few oxygen molecules in the exhaust, a P2099 code will be stored and a malfunction indicator lamp may illuminate.
Severity & Symptoms
A P2099 code indicates that the post catalytic converter O2 sensor on bank 2 has detected a rich exhaust condition. This can compromise fuel efficiency, so the code should be addressed as severe.
Symptoms of a P2099 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
Diagnosing a code P2099 may require the use of a diagnostic scanner, digital volt ohmmeter (DVOM), and a vehicle service manual. All Data (DIY) is also a valuable source for system wiring diagrams and other application-specific information.
Before attempting to diagnose this code, ensure that the engine is running efficiently. Address any misfire codes, throttle position sensor codes, manifold air pressure codes, and mass air flow sensor codes first.
Start by visually inspecting the system wiring harnesses and connectors. Pay close attention to harnesses that are near hot exhaust pipes and manifolds, as well as those near sharp edges (such as the cylinder head).
Connect the scanner to the diagnostic port and retrieve all stored trouble codes and freeze frame data. Write down this information, as it may be helpful if the code is intermittent. Intermittent codes can be more challenging to diagnose.
If the P2099 code is immediately reset, start the engine and allow it to reach normal operating temperature. Let it idle (with the transmission in neutral or park) and use the scanner to observe the bank 2 O2 sensor input data. Narrowing the scope of the data stream to include only pertinent data will provide faster data response. Observe the downstream O2 sensor signal. If the engine is running efficiently, the downstream O2 sensor data should reach a mid-line and stabilize.
The DVOM can be used to check the resistance of the O2 sensor in question, as well as the voltage and ground signals for the O2 sensor circuit. Before testing the system circuit resistance with the DVOM, disconnect related controllers.
Additional diagnostic notes:
