P2099 Post Catalyst Fuel Trim System Too Rich Bank 2

P2099 Post Catalyst Fuel Trim System Too Rich Bank 2

OBD-II DTC Datasheet

Trim System After Catalyst Too Rich Bank 2

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to all vehicles since 1996 (Ford, Dodge, GMC, Chevrolet, Mercedes, VW, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

Every time I run into a P2099 DTC I know it means the powertrain control module (PCM) has detected signal input voltage from the downstream (after catalytic) oxygen (O2) sensor for the first bank of engines, which indicates that the content of oxygen particles is too low. Bank 2 is an engine group that does not contain cylinder #1.

The O2 sensor consists of a zirconia sensing element enclosed in a ventilated steel housing. Platinum electrodes are used to connect the sensing element to the wires in the O2 sensor wiring harness. The O2 sensor harness connects to the PCM via the controller network. The O2 sensor provides the PCM with real-time data on the percentage of oxygen particles in the engine exhaust compared to the oxygen content in the ambient air.

The exhaust fumes from the engine are pushed through the exhaust manifold into the tailpipe and through the catalytic converter. They then pass over the bottom O2 sensor. Exhaust gases pass through the ventilation holes in the steel housing and through the sensing element. Outside air is drawn into the chamber in the middle of the sensor through the wire cavities. In the chamber, the surrounding air heats up, causing the oxygen ions to produce (energetic) stress. Fluctuations between the concentration of oxygen molecules in the ambient air (drawn into the O2 sensor) and the concentration of oxygen ions in the exhaust cause voltage fluctuations. These vibrations cause the oxygen ions inside the O2 sensor to bounce very quickly and repeatedly from one platinum layer to the next.

Voltage changes occur when bouncing oxygen ions move between platinum layers. The PCM recognizes these voltage changes as changes in the oxygen concentration in the exhaust gas. These changes reflect whether the engine is running lean (too little fuel) or rich (too much fuel). The voltage output from the O2 sensor is lower when there is more oxygen in the exhaust (lean state). The voltage output is higher when there is less oxygen in the exhaust (rich state). This data is used by the PCM, among other things, to calculate fuel strategy and ignition timing.

Once the PCM enters closed loop mode, if the O2 sensor circuit input reading downstream of bank 2 reflects too few oxygen molecules in the exhaust, a P2099 code will be stored and the malfunction indicator light may illuminate.

Severity and symptoms

A P2099 code means the Bank 2 downstream O2 sensor has detected a rich exhaust condition. Fuel efficiency may be impaired and the code should be considered serious.

Symptoms of a P2099 code may include:

• Reduced fuel efficiency
• Lack of overall engine performance
• Other related DTCs may be stored
• Service engine lamp will light up soon

reasons

Possible causes of this engine code include:

• Bank 2 catalytic converter defective.
• Defective MAF or manifold air pressure sensor.
• Defective O2 sensor bank 2 / s
• Burnt, frayed, broken, or disconnected wiring and / or connectors
• Engine exhaust leaks

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

A diagnostic scanner, digital volt ohmmeter (DVOM), and vehicle service manual will be helpful in diagnosing the P2099 code. All Data (DIY) is also a great source for system wiring diagrams and other application-specific information.

The engine must be running efficiently before attempting to diagnose this code. Misfire codes, throttle position sensor codes, manifold air pressure code, and MAF sensor codes must be reviewed before attempting to diagnose a P2099 code.

Begin by visually inspecting the system wiring harnesses and connectors. With the P2099, I would pay particular attention to harnesses that are routed near hot exhaust pipes and manifolds, as well as those that are routed near sharp edges (cylinder heads).

Connect the scanner to the diagnostic port and retrieve all stored DTCs and freeze frame data. Write down this information. This can be useful if it turns out to be intermittent code. Intermittent codes are more difficult to diagnose.

If P2099 resets immediately, start the engine and allow it to reach normal operating temperature. Let it idle (in neutral or parked). Use the scanner to monitor Bank 2 O2 sensor input. Narrowing down the data stream to include only the relevant data will speed up the data response. Observe the signal of the lower O2 sensor. If the engine is running efficiently, the data from the underlying O2 sensor should average and settle there.

The DVOM can be used to test the resistance of the O2 sensor in question, and the voltage and ground signals for the O2 sensor circuit. Disconnect applicable controllers before attempting to test the system circuit resistance with the DVOM.

Additional diagnostic notes:

• The downstream O2 sensor should not operate as often as the upstream sensors (after the PCM has entered closed loop mode). If the lower sensor continues to run as often as the upper sensor after the engine has warmed up and the PCM has entered closed loop mode, suspect a faulty catalytic converter.
• When a catalytic converter replacement is needed, consider OEM quality components. Refurbished or non-standard replaceable converters usually fail quickly and repeatedly

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