if the exhaust system heat shield is gone in my california FD, could this cause the yellow "check engine" light to come up? in other words, is there a feedback to the ECU?
camorra

 

I doubt that a missing heat sheild would affect anything with the ECU. I've removed a few of mine(heat shields) with no issues. Try resetting your ECU. Unhook battery, while unhooked pump the brakes a few times and reconnect battery, start car. See if that works.

 

I think missing too many heat shields MIGHT be able to cause problem(s).

The exhaust overheat sensor is mounted inside the car on the floorboard under the right-hand passenger's seat. According to my read of the wiring diagram in the ’93 manual this circuit is also linked to pin 21 of the ECU.

I didn't find any check engine error code listed, but since it shows to be connected, it might (1) flash the warning light, (2) generate an undocumented error code, and/or (3) change some aspects of the engine's operation in an attempt to lower exhaust temperatures.

’93 manual section F-189 details how to test the sensor itself.