### help-stck 02 sensor reads steady3.5v?!?!

[PC5505]

I have mmcd and my O2-F reads a steady 3.5 volts, at all times, even when the sensor is unplugged. I checked the sensor for continuity according to the service manual and got nothing so I know it doesnt work. My ECU hasn't thrown a check engine light though.

Does anyone have a clue why my ecu would be reading 3.5v or why it would not be throwning a CEL? What could it be getting voltage from when the sensor is unplugged?

Its a narrow band sensor so I know it shouldnt read more than 1v ever. My fuel mileage has sucked for a long time so this would seem to be the culprit...
I looked at the wiring harness that goes to the O2 sensor and it includes the wires for my temp sensors(3) and what lookes like a ground wire thats not attached to anything. The ground wire is just bare, woven grey wire, which I assume is supposed to ground at the down pipe but is not. I have an aftermarket DP and the O2 housing was eliminated(previous owner's work). The O2 bung is welded onto the DP in a place that makes it tough to remove the sensor without unbolting the DP. So I ran a wire from it to the DP to see if it changed the 3.5 reading and it did not..... I cant find anything in the forums about this and I'm stumped.

 

[steve]

Does anyone have a clue why my ecu would be reading 3.5v or why it would not be throwning a CEL?

Sure that's an easy question. O2-F isn't the O2 sensor on a DSM, O2-R is. O2-F is the front bank O2 sensor on a V6. What your looking at is just the value of a location in the ECU.

Steve

 

[PC5505]

thanks, that was very helpful. I was told by another dsm'r that the O2-R sensor had something to do with hill climb/under load fuel trims or something. Mine doesn't cycle, at idle it says zero, but was reading between 0-1 when under load last I checked, a few weeks back so I assumed he was right.... because it didn't cycle. I dont know, I guess I'll just replace the O2 sensor and see if that changes. Is it okay to go with the bosch version, its only $70 at shucks, though, I'm sure it can be found cheaper. Mitsu wants $160 for theirs... I ask because I came across a thread where several members mentioned having problems with the bosch and regretting taking the cheaper route.

 

[steve]

Sparkplugs.com has a denso OEM-fit for like $60

Steve

 

[PC5505]

got the one on sparkplugs.com, the denso, not the ngk, only a couple bucks more and I know denso is the top of the line. thanks steve.