O2 Sensor Troubles

[jcogley]

My 99 Q45 thru a PO140 noting that it faulted to an open circuit (bank 1, sensor 2, (one before the cat)). I changed the sensor and light stayed out for approximately 1.5 week, (300 miles). The car just thru a P0138 "O2 Sensor Circuit High Voltage" at the same sensor. If I'm correct, high voltage notes a rich condition. The previous owner noted that he changed the first O2 less then 4 months ago. I'm wondering if I have a bad connector/harness. Anything else upstream that would cause the O2 sensors to go bad? I know the O2 sensor tries to adjust lean/rich conditions. If I'm correct, high voltage notes a rich condition.

Another poster noted that it may be the ECU.

Anyone?

[Q451990]

There are a lot of posts on cascading O2 sensor failures in the Y33, but I honestly haven't heard of a real solution for it yet. I wonder if it would be worth your while to check all of the other engine parameters to be sure everything is operating properly... e.g. power balance, sensors, etc. Then maybe you could change all of the sensors at the same time - assuming you're at over 80K miles, it may be time for general maintenence anyway.

Hopefully some of the Y33 guys will weigh in soon.

Good Luck!

Heath

[Q45tech]

OBD2 is finicky and O2 sensor frequent [every 60-70k] replacement is part of the cost you pay for ease of diagnosis.

Are you using ethanolized substandard fuel..........early use of cheap dehydrating agents often created a build up of caustic sulfur compound on O2 and in the cats.

Probably not in Mississippi.

We keep all the O2 in stock for 97+ vs none for 90-95 Q and we have 10 times the number of customers with early Q so you can guess at the failure rate.

[qship96]

not on my 96.....188,000 on original o2 sensors you guys at t3 must see an awful lot of fragile q45`s

[maxnix]

OBD2 is finicky and O2 sensor frequent [every 60-70k] replacement is part of the cost you pay for ease of diagnosis.

One secondary sensor replaced at about 67K. Can't remember if there was ethanol in Puget Sound for the winter formulation.

[jcogley]

Frustrating because it's the same sensor, (Bank 1, Sensor 2), i.e, 2 in past 3 months. Notably this car has 43,000 miles.

Could a misfire cause the rich issue, (PO138 Code "high voltage").

Also, can anyone tell me, does the O2 Sensor automatically fail to rich if it's "open", (PO140)?

[bullittandy]

Swap sensors side to side, then you'll know, at least, if its the sensor. If the code doesn't "move", then its the wiring (unlikely-but check) or more likely the computer. If its the computer then its under warranty for 80K miles.

[Q45tech]

1996 is very different from 1997 entirely different engine..............OBD2 on 1996 was not fully implemented enough to meet minimal Federal specs but nothing more.

It took 4 years to fully comply with all the subparagraphs and details.

Even 2001 models left things out, not until expensive wide band O2 were used did system really monitor everything with redundancy.

In these transitional years 1996-2001 good to actually MEASURE emission on a dyno to double check for failed cats and other hidden items.