med_reject

if you get

DTC 13 - Bank I (Left) Heated Oxygen Sensor (HO2S) Circuit (Open Circuit)
DTC 63 - Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Open Circuit)

One sensor is stuck at .448v and the other fluctuates between 2 #s, .448 and .453, is it safe to say that the o2 sensor is not heating up, or could it be the actual sensor itself?

The left sided o2 sensor was replaced with an ac delco unit 5months ago. Im getting less than 150miles per tank!!

shoebox

Could be a power problem since it is affecting sensors on both sides. Check fuses.

med_reject

I did find it odd that both sensors could go like that. Im not good at reading electrical diagrams. it seems like both banks connect to the "Underhood electrical centre 2 - Engine sensor fuse, 20A"

In the owner's manual, the underhood fuse #2 says fog lamps, 20A. Does this fuse also do sensors??? My fog lights are working, so if its the same fuse, then the problem would more likely be in both sensors/wires...?

Injuneer

According to the wiring diagrams on Shoebox's website for the 95 A4 cars, fuse #6, 10 Amps, in the underhood box feeds the two O2 sensor heater circuits, plus the EGR and EEC solenoids. Are you having problems with either of those solenoids?

kingman109

hmm thats funny - cause im getting similar problems with my O2 and my EGR valve - after examining my fuse box i see previous owner has all wrong fuses in place...

med_reject

I checked fuse #6, (fans / actr in my manual) and there is no break in it. So im thinking that fuse is good, also my cooling fans do work, but I do not know if my egr or eec is working.

how do i check if its the powersupply to the o2sensors?

Injuneer

When you turn the key on and start the car, you should get 12V across the black and brown wires to each O2 sensor harness connector. If you get 12V on the harness, check the resistance across the pink and black wires on the sensor. If its "infinite" you have an open in the sensor heating element.

med_reject

man, u know ur stuff. one thing i forgot to ask, if a sensor is not getting power, should it not put out zero volts?

med_reject

Got the car on a rent-a-hoist and took a look down below, dealership unplugged both sensors and forgot to plug them back in. One of the plugs melted on the exhaust pipe. They never did figure out that the ignition switch needed replacement, I found that out off this forum and got the instructions of shoebox's site.

I am amazed that an unplugged sensor would give any voltage at all to the pcm???