Diagnose Oxygen and A/F sensors on a 99 Camry, 4cyl

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Diagnose Oxygen and A/F sensors on a 99 Camry, 4cyl
Hello everyone,
Anyone know how to diagnose Oxygen and A/F sensors on a 99 Camry, 4cyl? No trouble code has been set but the car has 130,000 miles on it and gas mileage is starting to decrease.

I am using an Autoxray, EZ Scan 4000. I do not know what any of the data that is generated means much less how to use it to diagnose a sluggish Oxygen and or A/F sensor.

I went to the Autoxray web site but the site did not have any info on what scanner readings mean.

Any help would be appreciated. Any reference material or web sites would be appreciated.

I would really like to know if I need to replace one or both of these sensors. They are very expensive and replacing either one without the facts to diagnose them as faulty or sluggish just does not make good sense to me.

Thanks for your help in advance!

Here are the readings I got:

Readiness Monitors:
Fuel system=closed loop
Load value=81.5%
Coolant temp=185 F
Short term fuel trim = -3.2%
Long term fuel trim=1.5%
Map sensor=24 in.hg
Rpm=2042
Speed= 29mph
Ignition timing advance=23.0 degrees
Intake air temp= 113 F.
Throttle position=24%
Oxy sensor #1bank 1=0.885 volts
Oxy sensor #1 short term fuel trim = -5%
Oxy sensor #2 bank 1=0.505 volts

02 Sensor Tests #1
low volt switch time =0.400v
high volt switch time =0.550v
min sensor volt=1.275v
max sensor volt=0.000
02 Sensor Tests #2
min sensor volt=1.275
max sensor volt=0.000