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Originally Posted by ttoyoda
OK, but I guess I think of dcb as the Linus Torvalds of *this* project.
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OK. I have to agree with you.
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Thank you for the links. 
While my ability to read Japanese is only as good as it ever was,  I see from the data sheets that on A3 Injector you picked a transistor 2sa1015 good for a minimum of 50 volts, and a high speed switching diode 1s2076. So I assume you must have been aware of the possible spike, (or if you were like me long ago, you tried it first without one and fried the chip) and you specifically picked a high speed diode to clamp it.
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Thank you for your comments. Your assumption is correct.
In addition to kill the spikes, we install the interface circuit close to the ECU, then the logic level square wave goes to SuperMID unit through LAN cable (twisted pair lines).
I didn't want to reach the noisy injector line to the unit.
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Can you tell if there have been any statistically significant in-the-field failures of the SuperMID that would trace back to a spike from the injector line with your current design?
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We delivered over 200 unit in the field, and we never heard any failures on the interface circuit.
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Also, I understand that the poly-switch is a self-resetting fuse, but did you feel the need for it other than "good practice"? Is there some particular risk that mandates it?
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Yes, it is 0.5 amp poly-switch and it's just for safety.
Without the poly-switch, the fuse for ECU will be blown when a power line short problem occurred, then we'll see critical vehicle failures.
Yoshi