Check engine light turns on for glow plug fault

My car gave a check engine light. I went to AutoZone and used their loaner scan tool to find that it was P0380 glow plug heater circuit A electrical fault. And cleared it. It did not turn back on during the drive home from AutoZone.

Why would the check engine light turn on for glow plug faults when there is a glow plug light in the dash? And the glow plug light turns on for a brake lamp switch fault?

The engine light turns on for a glow plug fault because they're emmissions equipement. The glow plug light blinks for a brake light switch fault because it blinks when there is an electronic management issue.

-Jason

The funny thing is, the car almost never gets started in below freezing weather (and it was certainly not anywhere near that temperature during the heat wave when the check engine light turned on). So the glow plugs in the car are largely unused.

Actually, they are used. They run until the engine starts to come up to temp. This reduces emmissions, and why a faulty plug trips the CEL.

-Jason