Severity and Symptoms
A P2099 code means the post-catalytic converter oxygen sensor on bank 2 has detected a rich exhaust condition. Fuel efficiency may be compromised and the code should be considered severe.
Symptoms of a P2099 code may include:
- Decreased fuel efficiency
- General lack of engine performance
- Other associated diagnostic trouble codes may be stored
- Illumination of the service engine soon light
Causes
Possible causes of this engine code include:
- Faulty bank 2 catalytic converter
- Faulty mass airflow sensor or manifold absolute pressure sensor
- Faulty bank 2 oxygen sensor(s)
- Burned, chafed, 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 (TSBs) for your specific vehicle. Your issue may be a known problem with a known fix published by the manufacturer and can save you time and money when diagnosing.
A diagnostic scanner, a digital volt ohmmeter (DVOM), and a vehicle service manual will be helpful in diagnosing a P2099 code. AllData (DIY) is also an excellent 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 absolute pressure codes, and mass airflow sensor codes should be addressed before attempting to diagnose a P2099 code.
Begin with a visual inspection of the system wiring harnesses and connectors. With a P2099, I would pay particular attention to harnesses that are routed near hot exhaust pipes and manifolds, as well as those routed near sharp edges (cylinder head).
Connect the scanner to the diagnostic port and retrieve all stored trouble codes and freeze frame data. Write this information down. This may prove helpful if this turns out to be an intermittent code. Intermittent codes can be more difficult to diagnose.
If the P2099 immediately resets, start the engine and allow it to reach its normal operating temperature. Let it idle (with the transmission in neutral or park). Use the scanner to observe the input data from the bank 2 oxygen sensor. Limiting the scope of the data stream to include only relevant data will allow you to get a faster response. Observe the downstream oxygen sensor signal. If the engine is running efficiently, the downstream oxygen sensor data should reach a midpoint and settle there.
The DVOM can be used to check the resistance of the oxygen sensor in question, as well as the voltage signals and grounds for the oxygen sensor circuit. Disconnect associated controllers before attempting to test system circuit resistance with the DVOM.
Additional diagnostic notes:
- The downstream oxygen sensor should not switch as frequently as the upstream sensors (once the PCM has entered closed-loop operation). If the downstream sensor continues to switch as frequently as the upstream sensor, after the engine has warmed up and the PCM has entered closed-loop operation, suspect a faulty catalytic converter
- When catalytic converter replacement is necessary, consider an OEM quality component. Rebuilt or inferior quality replacement converters typically fail quickly and repeatedly