02 sensor questions

[leakyfaucet]

I've noticed my o2 sensors haven't worked since I bought my car about a year and a half ago. The car had one o2 sensor plugged in, and the other had the wires cut. So I replaced both o2 sensors. I get check engine codes for both sensors failing to turn on as well as terrible gas mileage and black tailpipes. I think it's safe to say they aren't working. Someone suggested to me that my o2 sensor harness might be to blame. I checked it with a multimeter last night and every wire can carry a signal. So that's not it.

It's possible that I just bought the wrong type of o2 sensors but I really doubt that since it plugs in perfectly and is a 3 wire type. I'm not the type of person that just randomly buys things in the hope of fixing a problem (because I can't afford to.)

I was thinking of testing the harness with the car on and running and seeing if the plugs that go to the o2 sensors are getting any voltage. That way if they still aren't, it could be because of the harness before it, or another problem. Would that be a good way to test it? Anybody have any idea about what voltage I should be seeing at the o2 sensor plugs?

 

[jrichker]

Code 41(Right O2 sensor) or 91 (Left O2 sensor) - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.
The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel.

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.
The O2 sensor ground is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than .4 volt. Remember lean = less voltage.

" When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than .6 volt. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage."
Charles O. Probst, Ford fuel Injection & Electronic Engine control

 

[leakyfaucet]

So i can't check the harness to see if the sensor is getting voltage?

I'd like to check at the computer to see what the sensors are doing. Where is the computer? I've never had to pull it out. Is it under the passenger seat or behind the radio or something?

 

[cdog301]

puter

It is in the passenger side kick panel forward of the door

 

[leakyfaucet]

Hey, the only computers I've had to deal with were imports, which were behind the radio