jhg41977

2 for heat, wouldn't one be a ground?

Crush washers were on the oxygen sensors. They were not pretty but they were there.

I'll pull the heat exchangers off, clean up the flange on the cat an heat exchanger and also clean the bungs.

Quadcammer

yes, but that just grounds the heater. now that i'm thinking about it, i'm pretty sure the sensor grounds through the exhaust

nine9six

Jay J,
Do you have the adobe acrobat file of the 993 Workshop Manual?
If so, search for "ground strap"

HTH

jhg41977

If it were a ground issue, I should see the same behavior out of all four sensors. I'm only seeing signs of life on three and not all at the same time. I still plan on checking the ground.

BesideTheBox

I found this Bosch publication online last year when I was researching oxygen sensors.
This PDF has some great explanations of oxygen sensor operation and diagnosis.
The oxygen sensor in the 993 is the 4 wire variety.
www.bosch.com.au/car_parts/en/downloads/Oxgen_Sensor__Cat_WEB.pdf

Here's a link to a post about grounding points for anyone that might be interested:
https://rennlist.com/forums/993-foru...problem.html#5

bcameron59

Jim, did you ever get to the bottom of your O2 sensor issues?

My right pre-cat just stopped working, looking for info on how others solved theirs. Sensor has less that 200 miles on it.

Thx/Brian

jhg41977

I got so busy I forgot to post my findings.

One O2 sensor had a pinched wire, I think between the engine tin and chassis. Obviously is one is bad for sure. I am not sure if this created an issue with all of them since one now had a ground where it shouldn't.

I had already purchased four new sensors, so I installed them all. Two looked like hey may have been replaced, two looked like they could be original. I figured it wasn't worth chasing another few months out of them. Maybe I would have gotten longer, I don't know.

With all new sensors, the codes have not come back.