What would cause a 1994 Toyota Corolla to throw crror code 12?

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I discovered the problem. The problem was a bad distributor, which I discovered while doing a tune-up of the car. I removed the distributor cap to install a new rotor and was surprised to find copper wire fragments inside the distributor cap--big red flag. I look at the distributor armature and found that the fragments appeared to have some from this armature, so I immediately ordered a new one. I installed the new distributor and the warning light was gone. Problem solved. It would be remiss of me if I didn't mention that Scotty Kilmer had suggested that the distributor was the problem weeks before I discovered it, myself.