MaxPower

You can test the sensor on your car if you have a multimeter.
Yup

sive ick

its a 4 wire o2,which wires would go to what,i need to get some side molding from pick and pull i hope,i was just going to grab a 02 sensor to see if that is whats causing the rich mixture,if both o2 sensors are causing it to run rich it would help me narrow down what else could be causing it,the car had been sitting so i plan to change every fluid and the spark plugs,and add some fuel injection cleaner

but all that is pointless if i keep having a check engine light

MaxPower

If you have a multimeter I can walk you through on how to check the O2 and the wiring. Its not that hard.

sive ick

well yes i have one,but i have school so if you could pm me or post on here how to check it and i will do it when i get home,thanks alot for the help 'maxpower'

MaxPower

No problem

also did you buy a OEM O2 or a knock off?

sive ick

i havent bought a new one yet i just read off other forums about this electrical parts cleaner and have that a try

MaxPower

Ok well OEM all the way when it comes to emission devices, it cost more but thats for better quality.

I guess I'll start with a basic run through of what an O2 does.

The four wires are for ground, signal, and heater. One wire is the ground so the ECU can control it, two of the wires are for the heater coil, and the last is for the signal.

The signal an O2 will produce on a multimeter/scope is on a one volt scale. When an O2 is doing its job is will go from .2v-.8v(lean-rich) a couple of times a sec. The whole point of it going from lean to rich is for emissions, when it goes lean its starves the cat of HC(hydro-carbons/octane) and CO(carbon-monoxide) cleaning up the air (oxidation) but by doing this the cat gets real hot (above 2500F) and creates NoX(smog) so it goes to rich again to cool it down and reduce NoX. The amount of times a O2 goes from lean-rich in a sec is its crosscounts. The older a O2 gets the crosscounts gets smaller and the range gets shorter.

So when you go to read the signal out of your O2 the signal should fluctuate. The only problem is that a multimeter is SLOW so it wont tell us how good or bad you O2 is, it will only tell you if its working or not. Now your going to have to find a manual for your car since I don't know anything about a Jetta.

When you find the O2 sensor signal wire you will put your positive lead from the multimeter on that wire and the negative lead goes to a known good ground.
In the manual it will tell you what to expect when it comes to crosscounts and voltage range for a standard O2.

If thats good then you want to test for continuity of the signal wire to the ECM. Set your multimeter for resistance(looks like a horse shoe/omega) Put your positive lead on the signal wire from the O2 sensor and negative lead on the signal wire going to the ECM. If you have more than .5 of resistance there is an open or too much resistance and thats your problem.

When your testing for the signal voltage have you car on or with power and when testing for resistance have the car off.

I think I got everything right

sive ick

thanks man