I towed a car trailer 600 miles round trip yesterday and had a CEL light pop on the dash less than a hour into the trip. The stored code was p219b, bank 2 air fuel imbalance. The CEL went off on it's own after two drives without the trailer attached.
The truck was definitely working hard on grades and power was lower than expected for a 5500lb load. Since the code points to passenger side bank 2, what are the likely areas to troubleshoot? 2011 GMC Yukon 5.3l, 210k miles. O2 sensors, plugs and wires have 50k on them, clean air filter, fuel pump replaced 6 mos ago.