Yes they do. They can tolerate engine bay heat, but not exhaust heat. They are usually shielded from getting soaked.

Some Mazdas put the metal-cased engine computer in a plastic air box that feeds cold air from the front, to help ensure the engine computer stays cool enough.

In general, I believe the cooling airflow from the frontal air and the cooling fans keeps engine bay in check.

For example, this is the board that’s used in Mazda CX-5 2017+ engine computers (mfr Denso), it lists max temperature range of +150C: https://www.renesas.com/en/document/mah/rh850e1l-users-manua...

Yeah, on the Cummins the ECU is mounted on the intake side of the engine away from the exhaust and turbo and toward the front right under the fuel injection pump so it gets lots of cooling air.

This thread is interesting to me 'cause I'm also a software guy and recently took a job dealing with building fighter jets and the amount of engineering going into the wiring and computers on those things is insane. It's been a very interesting learning experience.