The control unit detects an air/fuel mixture on bank 2 with too much fuel relative to air. The fuel trims reach their lean limit while trying to compensate.
Common causes
Leaking or dripping bank 2 injectors
Excessive fuel pressure or faulty pressure regulator
Contaminated or faulty mass air flow (MAF) sensor
Very dirty air filter
Coolant temperature sensor falsely reading a cold engine
Faulty or slow upstream oxygen sensor
Symptoms
Black smoke from the exhaust
Rough idle and uneven running
Poor fuel economy
Black, fouled spark plugs and fuel smell
Check-engine light on
Severity
Moderate: the car is drivable but uses more fuel, and the excess fuel can foul plugs and damage the catalytic converter over time.
What to do
Read the fuel trim values (short and long term) to confirm the rich condition on bank 2
Check fuel pressure and bank 2 injector sealing, looking for any dripping
Check the MAF and coolant temperature sensor signals, cleaning the MAF if it is dirty
Inspect the air filter and assess the response of the upstream oxygen sensor