GM 3.1, 2000 Malibu, P0135 code

[jstutz]

I have my moms car which needed the lower intake manifold gaskets changed. She has always had a CEL on for an EVAP issue. Well after changing the gasket, letting it sit over night. It started up and runs perfect. I figured i would work on the EVAP issue so i plugged in my scanner tool and P0135, bad 02 heater circuit. I dont know if it was there or not. I retraced everything i did in my mind and dont know what i could have done to cause that. I checked the 02 sensor and the wires are connected. I did not disconnect them. The code pops on immediately so it makes me think it is a shorted or open wire. Usually when things like this pop up is some connector that gets overlooked or something. I cant find anything that did not get connected. Im guessing there should be some voltage to the sensor so if i disconnect it i should be able to tell if it is getting the voltage required. Does anyone know what the proper voltage should be. I have found information on other sites about other vehicles but im not sure it is universal. I also know that sometimes 02 type codes can pop for other reasons other than the 02 itself. Also is there a fuse for the 02 sensor?

 

[Trav]

The heater circuit is 12v, if there is no voltage look for a fuse, the owners manual is the best place to get the fuse block diagram.
Check the grounds with a DVOM set on ohms it should read zero.

 

[jstutz]

Hey guys here is a update. I dont see a fuse anywhere. I have a ultragauge scan tool i forgot about and it measures output of the 02 sensor. I plugged it up and both 02 sensors read between 0 and .9 V while running. Then when i got home, i checked the black wires, which i think are the heater ckt wires. Well one of them is 13V to battery GND and also 13V from the other black wire. I believe this rules out a broken wire. I dont know how to check the actual 02 sensor side because i dont know what it should read. Im guessing it is some sort of resistance but i dont know the value. Any inputs will help.

 

[jstutz]

I found a document that was related to testing 02 sensors and it explained that the heater ckt should be a low resistance up to 5 ohms when cold and has a positive temperature coefficient. I measured across the two pins that are labeled heater ckt, i get an open ckt. I believe this confirms it is a bad 02 sensor. The only variable is if for the heater ckt, i dont know if both black wires should be hot and it is grounded thru the sensor it self. If it is how i think it is, one wire hot and the other GND, then i have confirmed that the sensor is bad.