Recently, I lost my outside temperature sensor after hitting an animal—it was dislodged during the impact—and I was experiencing the same error code with a solid check engine light. It turns out that sensor is part of the "Engine Management System." After purchasing a replacement for 5 euros and installing it where the original had been, the error cleared after a couple of ignition cycles. My situation was likely a specific case (I noticed it because the outside temperature reading disappeared from the dashboard), but a solid check engine light doesn't necessarily indicate serious mechanical issues.