If there was an oil pan leak that leaked directly onto the coupling for the o2 sensor; could that possibly cause the o2 sensor to read lean and send code 172 even though air/fuel mixture is fine?

 

If the oil interfered with the electrical connection then I would suppose so. Is the lean condition on the side with the oil soaked sensor? Have you checked your A/F with a gas bench?

 

I have only one o2 sensor in the cross over pipe. I assume by A/F you mean air fuel mixture? No I have'nt. Everyone keeps telling me it is an air leak in the vacuum system, but I have checked and cant find a hole. Besides; the hesitation/surge I get goes away for 1,000 miles if I replace the o2 sensor. And it runs perfectly during the 1,000 or so miles. I fixed the pan leak, and put in a new (again) o2 sensor. So we will see. If it was a vacuum leak, It would still run lean after putting in a new o2 sensor. Some how either by short or whatever, I am "blowing out" o2 sensors.

 

i'm not sure what year truck you have, but on my 97 4.6L, the ac drain was leaking onto my O2 sensor and blowing it out. i had to install an ac drain hose, that either fell off my truck, or was never on it. run the ac and drive for a while then when you stop get under the truck to make sure nothing is dripping on the O2 sensor.