01 Ram 1500 had the CEL come on for downstream 02 Sensor. Truck was sluggish with no power and had no vacuum when giving it gas (have a vacuum gauge). So I found a vacuum leak under the airhat and ran a 3 part system cleaner through the engine (one you put in the gas, another you clean the throttle body with, and lastly one you run through your vacuum hose I used the brake booster vacuum line). Then I cleared the code and it hasn't come back in. Before the CEL would come on for a few days then go out but if you drive less then 20 miles would consider back on for a few days. Now I have a Snap-On scanner that can read live data. How can I test the 02 sensors, more importantly the downstream, using the scanner? I have no idea what they are dopesup to do. Thanks Austin!

 

Sensor voltage should switch high/low with engine running. Anywhere from .1 to .9 volts. If you see the voltage changing, sensor is 'working'. Rear O2 just monitors cat efficiency though. What code are you getting?

 

I forget the code but it hasn't come back on I think the rear was reading 3.xx volts and the front was 1.xx - 2.xx volts. If I have to replace them isn't NTK the best brand for our trucks?

 

If they go over 1 volt, they are bad.

Yep, NTK I think was OEM, Denso works as well. Bosch, however, does not.

 

That's odd because I never got a code for the pre cat O2 sensor. It was in closed loop because code was still active when I was monitoring it.

 

On your snap-on scanner? Those are usually pretty good. I have never seen an O2 go over .9 volts, when it was actually working right.....

 

Maybe your cat is plugged?

 

Looks like downstream is bad and the truck runs great now after I did everything! But bad gas mileage, maybe cat is bad? But here are two pictures taken during the live data.

 

Yeah, that's just wrong. Either the wiring is bad, or the sensor itself.

 

Yeah I bought an NTK