Hi Jessie,

There's no history of failures like that, and the circuit protection on the inputs makes it unlikely. But the dual-use thermistor (black) temp sensor depends on the head for a ground (hope no one used teflon tape there) and one of the black leads grounded under the fuel rail screws to return it to the ECU.

I could speculate the different ECUs may be responding unlike each other to an intermittent out of range signal, because they have different code versions, resulting in some variation of the symptom or diagnostic set. It does seem to center on the ECT, and there's no implicit expectation the ignition CU would vindicate the sensor's ground by not setting any fault codes.

I'd put my bets on a flaky connection within the harness rather than an easily replaceable part.
--
Art Benstein near Baltimore

Acupuncture is a jab well done.