[SoCal LS-L]

Originally Posted by Trevor

After noting the symptoms you described, my immediate reaction was to suspect the coolant temperature sensor. You have struck the jackpot. Check the wiring and if this is OK, replace the sensor. Not a big deal.

I would suspect that constant efforts to start the engine could well have registered a starter switch code. You did not mention any issue regarding starter operation. Ignore this meantime until you replace the sensor and clear the memory, when 12 should clear together with 21.

P.S. Check the how to section for a part number.

+1 Classic symptom of a bad temp sensor. If your computer is always sensing a warm engine and keeps the auxillary air valve shut, along with the closed-loop fuel maps, cold starts are a pain, if they happen at all.