What do you look for in a faulty oxygen sensor? What's usually the problem?

Question

my engine check light came on. went and got it scanned and it said it was a faulty oxygen sensor. but i forgot if it was the front or back o2 sensor. so what can u look for to tell which one's bad? and what are the typical problems of the o2 sensors, wiring or the sensor itself?

i got it scanned, forgot which one. went and got it scanned again, but the codes were cleared.

but the guy said he was pretty sure it was bank 1 front one. i have a VW jetta GL 2.0

and my car has about 85k on it

1999 1/2 VW Jetta GL 2.0

1999 1/2 because that's when VW changed up the Jetta

Answer 1

They'll both be in about the same shape, so you should just replace both of them. It's probably not the wire. You'd get a high voltage on the circuit code if that was off. The typical problem is that they just don't last the life of the car. If they're 100,000 miles old, they've had a pretty good life.

Answer 2

Most often, it's the sensor as opposed to the wiring.

If your car is 95/96 or more recent, an OBD2 scan will remind you of which sensor was bad.

If you own a voltmeter (preferably an old analog one), it's pretty easy to see an O2 sensor that's failing badly. When operating correctly, these sensors cycle somewhere between 0 and 1 volt slowly enough (several times per second) that you'll recognize a good one on an analog meter as the meter tries to bounce back and forth. They cycle too fast for you to really see it on a digital voltmeter -- these meters don't update the display fast enough for you to tell much.

There's a catch, though -- the meter you use should be spec'd for at least 1Mohm per volt to avoid loading down the circuit. Most less expensive analog meters are not while the digital units are. An analog meter often displays that information on its faceplate.

Of course, if you're one of the lucky dogs (like me!) who own or have access to an oscilloscope, you'll see the operation of these sensors with ease.


Note: your engine MUST be warmed up in order for these readings to be accurate.

Note: some sensors have their own heaters (3 wires vs. 2). If so, exercise a bit of care, because one of the leads (vs. ground) will be 12V and the other your 0~1V ox sensor output.


P.S. Found a pretty nice site on O2 sensors a while back. Just located the link again. Plain English.
http://www.mr2.com/TEXT/O2_Sensor.html

Answer 3

Most good shops will run the OBD tests for free so its best to see what O2 sensor is bad. if its a V 6,8,10 its probably got 4 different sensors.

Answer 4

Take it to a shop. But rerun the test to see if it tells you wich one. You won't be able to see the issue with the sensor unless its simply a bad lead. If it has alot of miles, its probably the sensor-- replace it.

Answer 5

bad sensor ,bad wiring,old spark plugs.

and, so ,on and on.