My RAM truck with the Cummins diesel engine has the engine computer mounted on the engine block. You'd think the heat and exposure to the elements would make that a bad idea, but I suppose Cummins knows what they're doing.

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phil21 8 hours ago | parent | next [-]

My car has it under the passenger seat.

Sounds alright until you realize after spilling a bunch of flower vases in the trunk (hatchback) that the computer has literally no case on it and immediately shorts out while driving. Or a passenger spills a drink in the rear seat cup holder.

There is now a recall notice to pull the back seat out to install a $5 plastic cover over the thing.

And yep, it’s the main computer for the car which controls the electronic transmission etc. Immediate full on engine-shuts-off at speed on the freeway and you require a flatbed to tow it away level of broken. I’m sure the engine ECU is in the engine bay, but holy hell what a surprise!

	▲	bdunks 8 hours ago \| parent [-]
		I had a car with an all wheel drive computer in a similar spot in the late 2000s. I had a small crack in the rubber seal around my sunroof from parking outside in the elements. When it rained, water seeped in, made its way down the a-pillar, pooled under the seat, and fried the computer. Expensive fix but I was able to drive it to the shop.

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kube-system 9 hours ago | parent | prev | next [-]

Hehe I was thinking about FCA/Stellantis vehicles when I wrote that. I know it works and there are components made to work in that environment but it always felt intuitively wrong to me. Especially when the other side of the firewall is a much better environment and not far away

	▲	yearolinuxdsktp 9 hours ago \| parent [-]
		It’s because when placed inside the engine bay, the large wiring harness is shorter, which is not only cheaper, but also shorter wiring helps with the consistency of electrical timing and reduces noise.

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cuvinny 8 hours ago | parent | prev | next [-]

Could be because they sale crate engines.

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yearolinuxdsktp 9 hours ago | parent | prev [-]

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...

	▲	msisk6 8 hours ago \| parent [-]
		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.