ABS Light comes on

Hi everyone! Right after I went through an automatic (touchless) car wash, my ABS light came on, stays on. After a restart of the vehicle, it goes off, but after 10 seconds up to about 60 seconds it comes back on again. I'm assuming a sensor is to blame, maybe it got dirty or mis-aligned? Anyone know, do these sensors use an optical mechanism, or magnetic or what to detect wheel rotatation (or lack thereof)? Vehicle is cutlass supreme, 1997.

Mike
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