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Stock JK TechBulletin board forum regarding issues with OE (original equipment) components of the Jeep JK Wrangler (Rubicon, Sahara, Unlimited and X) such as factory suspension parts, engine, transmission, body parts, interior fixtures and the on-board computer.
Block heater is probably what it is then. That certainly explains why it seems some don't have that. Mine doesn't either. If it was a knock sensor, they would all have it.