I cannot get my o2 sensor after my cat off cuz of the tight spaces underneath is there anything you can tell me that could possibly help it's on a jeep wrangler 2000

An upstream O2 sensor (on any vehicle) will be located somewhere on the exhaust system in front of the catalytic converter- between the exhaust manifold and the cat itself.

You may have to crawl underneath your vehicle with a flashlight and simply trace the exhaust system from cat to engine. The O2 sensor is screwed in somewhere -you'll see the connecting wires.

The post-cat O2 (emissions) sensor reports the exhaust gas condition to the engine management system and it is the pre-cat O2 sensor that closes the loop in the closed loop emission control system.

If the post-cat O2 sensor is reporting bad emissions it is because the pre-cat sensor might be faulty or the engine management system is failing to control fuelling because, perhaps, the injectors are dribbling, the spray patterns are bad, the fuel pressures are wrong or another sensor is sending incorrect information to the system.
It is also possible the CAT is defective or the exhaust or intake is strangled, etc...

Code 420 is for a possible problem with the catalytic converter. The computer uses data from the front and rear O2 sensor to monitor cat activity. The sensors are telling the computer the cat is not performing correctly.
The problem could be the cat or something else such as the fuel system.

You have a fail exhaust converter on bank # 1

Google the PO420 code & read up

your truck should have four o2 sensors bank 1 sensor 1 is o2 sensor on cylinder 1 side before cat and bank1 sensor2 two is 02 sensor after cat banks 2 sensor1 is on other side berfore cat and bank2 sensor2 is after cat hope that helps when they read code it should tell you bank1 sensor1 or2 good luck

there are 4 o2 sensors. one on each bank after the cat. converters, one before the muffler and one on the muffler.

chances are it one of the o2 sensors by the cat converters.

check you Mass Air Sensor and replace spark plugs, because there is probably something simple that wrecked your o2 sensor in the first place and it will help your vehicle run and last longer. It could be more complicated, like a vacuum leak cuz honda civics are known to have head gaskets replaced.

But i guess first you need to figure out which o2 sensor it is.

po420 and430 is telling that the catalyst converters are no good both, most of the time bad o2 sensors maake computer think cat is no good, the way it tests is if o2 sensor reading before cat is about the same as the one after cat computer asumes cat is not bruning exhaust good , iwould replace o2 sensors reset check engine light and go from there, that might be the problem,if you were to replace cat o2s should be done at that time,so do o2s first,good luck.

If O2 sensor is bad it can cause Rough running. Are you sure it is the O2 sensor ratteling? Have you taken it out to hear Rattle? Is it loose? I have not Hears an O2 Sensor rattle. I have heard Converters Rattle. over time Inner Material of converter will Not have a tight fit due to heating and cooling. expanding and contracting. carses some of the material to wear away. Causing the it to rattle. and can cause rough running also.

The O2 sensor is before the cat, the cat performance monitor (which looks like an O2 sensor) is after the cat.

"Up-stream" means before the catalytic converters and are probably in the header pipe(s). The "down-stream" O2 sensors are behind the cats in the exhaust system, usually just behind them. Not the expert here on this particular car but there are probably 4 of these sensors. BMW exhaust systems are very tight on space, be careful tackling this job.