Schematic for the ESide goes slowly, I realize how much info is missing. I wonder if anyone can help me with the part marked:
16383Y37
27474
DELCO 466
This part is a 28pin PLCC and along with it's neighboring part (144436 also 28 pin PLCC) handle limp home functions and ignition. I have noticed that the part has both analog and digital functions. It *looks* like the part monitors the ignition control analog and makes changes to the control path if it sees an error. I think control by the TPU is disabled under certain conditions and the 144436 part takes over with some default timing. The part is clocked or perhaps just inputs re-evaluated based on a relaxation oscillator. This is set up using an external r and c connected to pin 18. The components installed on my board result in a 2KHZ oscillator. The pin discharges the cap to 1.6V... resistor re-charges it to 3.4V--> results in a saw-tooth wave at the pin.
Note[Frequency is: f = 1/ ( -1 * ( ln(1.8/3.4)*(R*C))), This works out to 2148hz, measured is 2khz]
I know this part will reassign control of fan relay 1 in the event of fault. Perhaps just turns it on? Same with the fuel pump relay.
The operation of the part isn't clear to me. I don't quite know what it tries to do or how it detects a switch. Best guess right now is that the TSide is involved over the ribbon cable.
Can anyone lift a bit of the fog here? If no, there is significant testing to be done in order to uncover how the system works.
-Tom
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