Anodized aluminum & ground

[Charlie Guthrie]

The aluminum underneath the anodizing will conduct very well. The anodizing
is a ceramic, aluminum oxide (same as sand paper) and is a non conductor. If
you break through the anodizing you should be OK. If you are relying on
contact between  anodized screw threads and the engine block (or other
ground source) you may be disappointed, but you could get lucky. Since a
sensor draws very little current, even a small breakdown of the anodizing
will conduct enough to make the sensor work.
Charlie G
Raleigh, NC
'92 SE-R (designated mechanic)