Where is the rear O2 sensor in a 1995 corolla

I would start with checking the spark plugs and cleaning out the throttle body.

Clogged catalytic converter. remove the front O2 sensor, if it doesn't die, replace the converter. Bad coil.

sticking fuel enrichment solenoid, EGR control or valve leaking vacuum around stem. slow o2 sensor response.

P0140 - O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2

Possible causes- Faulty Rear Heated Oxygen Sensor Bank 1
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

Driving the car will not clear this trouble code, it has been stored in the ECU. You must remove the EFI fuse from the engine bay relay block for at least 60 sec, or disconnect the battery for that time.

Here's a link to your P0420 code and what could cause it. https://www.autocodes.com/p0420_toyota.html

for this code, you can try,
Replace O2 sensor.
Repair short to battery voltage in o2 sensor signal circuit.

The Check Engine Light can come on for any number of reasons when the engine's computer detects an abnormal operating condition. Frequently, it is related to a malfunction in a sensor or sensor circuit, like a O2 sensor, temperature sensor, and so on, but it could also be due to a misfire, or an emissions control problem, or another reason. On cars from 1996 and later there is a standardized connector for a scan tool (OBD-2) to hook up to the computer and identify the error code. But for 1995 and earlier it is necessary to access the computer's data link terminal under the hood and perform a diagnostic procedure to read the error code. You can find detailed instructions on how to do this on your car at www.autozone.com, or in your car's repair manual.

if the code is for the rear cat o2 sensor i suggested to replace the cat. the rear o2 sensor is to tell the commputer ha good is the cats if the cat not burning the gas. the commputer need to see the o2 sensor to check the cat's

Remove the plastic engine covering the top of the engine by removing the 2 10mm nuts. Pull the cover off and standing in front of the car looking at the engine,the pcv is located in the rear of the valve cover on your left. There is a 3/8 id hoses attached to it. Pull the hose off and unscrew the valve with a 22mm socket..
If you look down at your exhaust manifold you will see a sensor sticking out that looks like a o2 sensor. It is not. Its an air fuel ratio sensor and it works totally different then a o2 sensor.THis is the sensor that helps adjust the air fuel mixture. If you follow the exhaust system back under the car about 1/2 way you will see another sensor in the exhaust . This is the o2 sensor and is used to monitor the condition of the convertor.
If you need one of these sensors you will have a check engine lite on with a AF or o2 code.