P0134 code
 

So the service engine light stays on when I turn the key to position 2 (not starting the vehicle). Might be normal? It quickly goes out once the truck is started.
Decided to put the code reader on and got the ole P0134, it was the only code it threw.
O2 sensor circuit
No activity detected
Bank 1 Sensor 1
My initial thought was to quickly call Atlantic British and get 4 new o2 sensors.
However, in researching I have heard that people have replaced the sensors and kept getting the code.
Is there a list of things to check before I throw the $240 at the sensors?
Exhaust leaks?
I was seriously just hoping to buy the sensors, put them in and be done, I was surprised to hear it may not be the real issue.
Just a note... I replaced plugs and wires a few weeks ago.

Mil light will come on when you start the vehicle for the bulb check. Your fault code being bank 1 one before the cat, sounds like a dead 02 sensor. If there were adaptation codes for mixture control, I say maybe vacuum leak running to too lean. Switch 02 sensors before the cat left to right and see if the fault code goes to bank 2 sensor 1 Also if you had a OBD scanner with live data feed you could see if bank one sensor one is flat line not switching, compare it to bank 2 sensor 1.

At least replace both front 02's at your mileage.