p219b when towing

[alvocado]

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. 

[alvocado]

I think I tracked down an exhaust leak that likely tripped the CEL under trailering load. I hooked up a shop vac to the tail pipe in reverse, blew air through the exhaust system and sprayed down the passenger side engine and exhaust with soapy water and got suds at the downpipe flange. A new flange gasket should solve it.