Northstar Engines and System Technical Discussion Discussion, Pc1139 in Cadillac Engine Discussion; Everytime I get gasoline I get a Service Emissions Code. I can reset the code, but cannot find out what ...
Heated Oxygen Sensor switching fault, Bank 1 Sensor 2.
If you have 4 sensors, that sensor is in the exhaust pipe before the cat. If you have 3 sensors, that is the after-cat sensor. (1 sensor in each exhaust manifold collector area, and then as above.)
You might also check your gas cap and fuel tank fill pipe - a fault at fillup may be due to a fuel tank pressure/vacuum condition. Some vehicles in your year series have had problems with the upper fuel fill pipe rusting through.
For code definitions go back to the sticky at the top of the forum page or either Deville or Seville, use the thread "how to pull codes", open the link with "obd2" in the URL and click on the blue lines in the Master Index box to get definitions of the P,B,C, and U codes.