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After UIM cleanup I got 1131--Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1.

So... knowing not to trust most recent work I went ahead and promptly pulled UIM again. Well, in reality I needed to clean LIM too, so that was required anyway.

In the process I rechecked all the gaskets and everything seems OK. All gaskets are new, and this is like 5th overhaul for me, so I doubt it's my sloppiness. Idle is normal, the car feels normal, returns to idle fast.

Here's the weired part. When I watch the sensor in real time Bank 1 Sensor 1 reads anywhere from 0.05 to 0.9 at first. Later, as the car heats up (I guess) it stays near 0.1
Bank 2 sensor 1 reads from 0.1 to 0.8 all the time.

So I'm thinking it IS the HEGO sensor. I might have a slightly used from my '96 somewhere in the basement. failing that, I'll swap front and rear just to be sure it is indeed HEGO, and not a leak.

Opinions welcome.

One possible cause might just be that some cleaning fluid made it's way through a cylinder on the same side as the questionable HEGO and landed on the heated element - cracking it.

The sensing element is a ceramic matrix if I'm not mistaken and once hot it doesn't like cold stuff hitting it. The thermal stress is what cracks/kills the HEGO.

I had both of my upstream HEGOs quit within a week (with intermittent faults thrown in the mean time) of being stored in a cold damp garage last winter. When I started the car to pull it out and go home it stuttered and stalled then ran pig-rich for ~ 2 minutes before clearing out.

A question for you would be - did you leave the key on for about 20-30 seconds before trying to start? That's about how long it takes a HEGO to heat up.

J

To add to that same thought, the HEGO monitor isn't run for about 5 minutes because any excess moisture within the exhaust would damage/crack the element. the monitor is disabled until operating temperature is reached so that any moisture within that area will be evaporated.

ANY moisture at all is a bad thing for that element.


Ray