DTC P0172 system too rich bank 1

[cobra1]

This DTC shows up once in a while out the blue on my 2000 Blazer. It showed up again today. the last time was probably January.

im figuring it involves the O2 sensor, but which one is considered bank 1. also, is there anything else other than the O2 sensor that would cause this.

i have a scan tool that will give real time sensor values, but since its a rare intermitent problem, even that doesnt help much.

[Flatrater]

All GM cars and trucks work the same way. Odd cylinders are bank one even cylinders are bank 2. Sensor one is the first sensor sensor 2 is the next sensor usually behind the cat convertor. Sensor possitions start at the cylinders and go back.