AMSOIL has released a Technical Service Bulletin regarding Toyota, Lexus and Pontiac vehicles with Toyota-built engines that have reported that their vehicles’ oil pressure light has illuminated when extending engine oil drain intervals. Here’s an excerpt from TSB: EAO Oil Filters – Toyota Applications:

To protect the engine, the OEM has engineered the oil pressure sensor to trigger the oil light when there is insufficient oil pressure to maintain an adequate level of protection. Each filter is equipped with a by-pass valve, so when the filter is at or close to capacity, the engine is continually supplied with adequate lubrication oil, although unfiltered. However, if the filter reaches maximum capacity, the level of restriction can become significant enough to trigger the oil pressure warning light. In extreme situations, oil starvation could occur.

The TSB offers recommendations on avoiding this issue. This discussion dovetails nicely with a TSB from 2005 that was revised this spring entitled Using AMSOIL in Engines with Possible Sludge Issues.