Dcoy

I need to know if there is a way to test a O2 sensor? I have a 2000 cherokee with a 4.0 and it has 4 of them and they are to expensive to just up and replace all of them.................. Its a long story why I want to!

5-90

Not readily, on the bench.

The only tests I can think of are to test the heater element in the thing (which is explained in the FSM,) and to piggyback the thing in normal operation and check for a valid output signal.

Your 2000 is OBD-II. This is why you have four HEGO sensors - one before each of the pre-cats, and one after.

The "upstream" sensors monitor fuel trim - these are the ones that will have the most impact on fuel economy. The "downstream" units monitor catalyst efficiency - these have effectively nothing to do with fuel metering.

Spec life of a HEGO sensor for OBD-II runs 60-80Kmiles.

Now, what symptoms are you experiencing?

tjwalker

If you plan on keeping the vehicle, replace all of them at the same time.

From working with many OBDII vehicles, oxygen sensors have a finite lifespan of between 100k and 150k, depending on engine efficiency. Older vehicles didn't get this mileage from them, but it is very common for newer ones to. I have original sensors in my 99 with 150k. Gas mileage and performance is exactly the same as when I drove it off the lot.

I recommend NTK replacement sensors; the same as what are on your 2000. Search rockauto, amazon, etc. to find the best price.

Dcoy

Well if you really want to know my problem........my 2000 XJ is giving me a p0304, cylinder 4 misfire, and sometimes one about an very small evap leak. Basicly it starts and runs alittle rough then misses and runs real bad within a mile from where I leave ( this is when I get the code flashing) from then if I shut it off and restart it will run fine. only happens when the jeep sits for a few hrs, but never when its hot. I changed the plugs ( copper core) coil rail, cam sensor, crank sensor, TPS, the ECM, swapped injectors around, did a compression and fuel pressure test, ran seafoam through it and lastly checked the index of the cam sensor ( was good). Still having problems. Im just going down the through everything and trying to check it.

5-90

EVAP leak - check the vacuum lines, particularly the ones to/from the fuel tank and charcoal cannister.

Single-cylinder misfire? Coils, plug, corrosion in the plug threads (screws with the ground return,) injector problems with that cylinder, ...

rrich

None of those symptoms even come close to what a defective O2 sensor will cause.
Check the vacuum hose to the MAP sensor - must fit tight!

The evap small leak - fuel cap? Look closely at the hoses under the brake booster - often a smoke tester finds a small leak there.

Phil_XJ

Sorry to kind of hijack this thread but is it possible for damage an O2 sensor from overheating?

edit: I'm kind of in the same boat, I was looking for a way to test the sensor I just replaced prior to overheating (which solved the problem) but problem returned after and I can't find any good way of testing it. Although I only have 2 not 4.

rrich

Damage from overheating? Not likely except from a fire. They are designed to easily withstand 700+ degrees - the temp of an overheated cat.

Trying to test it with an Ohmmeter will instantly destroy it.