That is the low pressure switch. That switch actually measures the amount of brake pedal TRAVEL. When that switch actuates, it signals the ECM to check brake system pressure. If the pressure has not exceeded 500# with that amount of pedal travel, then you get C1282. So, it’s a brake pressure vs pedal travel check. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.