Thanks, folks. I should have been more specific. The 1st mechanic said CEL was an emissions code, but cleared it fine. Came back on. Cleared it again. Drove it for about 1 month and happened again. This time an independent mechanic specializing in Lexus repair said he couldn't locate a code so it must be the computer. Although I've never done this in the past, I did start "overfilling/topping off" my tank when I get gas ... don't even know why I started it. I see that other folks have had a problem with the CEL when they do this. I'm gonna change my bad habit (at least that one) and see if that's the problem. The mechanic did say that not properly tightening the gas cap can cause the CEL light to come on also. Thanks again for the input. By the way, a rebuilt Lexus computer runs $1,047 without installation (I think another $60).
