tl;dr: 6890 can’t recognize split/splitless inlet – is it the control board or the EPC?

Details:
The inlet of our 6890N was not getting any pressure. Everything else from the Back Inlet menu seemed normal. There weren’t any errors. I did all kinds of leak tests, cleaning, consumable replacement, etc and it stayed at 0 psi.
I thought it might be electronic, so (with the power off) I switched the ribbon cable that connects the EPC to the circuit board on the top/back of the GC from the Back inlet spot to the Front inlet spot. I moved the injection port to the front position along with the wires for the heater/thermocouple, plugged my autosampler into the spot for the front inlet, and messed around with chemstation until it recognized that the injection port was in front now. Ran a standard, it looked great, but the instrument’s display gave me an inlet error.

I restarted the instrument, and here’s what I get:

After Startup:
Front inlet read/write failure. Module is unusable.
Press STATUS key:
Exception(s) found.

After pressing [Status]
STATUS – not ready
AUX 1 temp
Oven temp
FAULT(s):
F Inlet bad cksum.

If the ribbon cable is removed, there are no errors, (but all I can do is adjust the temperature of the front inlet, which does work).
If I put the ribbon cable to where it originally was (for the back inlet), it now gives the same checksum error.
I tried cleaning the leads with canned air and a Q-tip since they were a bit dusty, but that didn’t change anything.

So I’m thinking the problem is:
a) Bad board on the EPC module
b) Bad EPC board
c) Maybe the ribbon cable but… that’s probably not likely, right?

I don’t have spares of any of these things (I’m not brave enough to pull them out of our instrument that is working). Any ideas about which is likely or if there’s a way to figure out which it is?