If only one bank shows either lean or rich, it is probably a failing O2 sensor. If both banks are registering rich or both lean, then there is an engine control problem because the chance that both O2 sensors have failed in the same manner is slim. To correct the failed O2 sensor, replace the front bank sensor with a Bosch 13942 from AutoZone or AutoZone.com for $33.99+tax. If the sensors have been in there longer than 60,000 miles, you should replace both of them. The Wells Manufacturing site recommends replacing the O2 sensors along with the spark plugs.
For the KOER test, you needed to look farther down the page for the test procedure. Also given below.
KEY ON ENGINE RUNNING (KOER) TEST
1. Make sure engine is fully warmed. If in doubt, run engine at 2000 rpm for 2 minutes.
2. Turn ignition off and wait 10 seconds for system to shut off. Make sure A/C is off and transmission is in Park (automatic) or Neutral (manual).
3. Hook up light and jumper (or tester if you have one).
4. Make sure vehicle is safe to run and start engine.
5. Engine I.D. should be output.
6. Step on brake and turn steering wheel 1/4 turn.
If the vehicle has an overdrive cancel switch, push it.
7. If a "Goose" pulse is received, move throttle quickly 1/2 way down and release.
8. Fast Codes are output (ignore).
9. Read codes.
10. See code explanations and check components as necessary.
Use FIRST CODE OUTPUT and retest after any repairs are made.
Scott