I think the DTC name: "Clutch interlock switch" may be misleading...
What if the ASCD / cruise control clutch cancel switch is sticking for 2.1 seconds???

When you read the DTC detection condition is says:
Detects that ASCD cancel switch is in the ON position for 2 seconds or more while ignition switch and clutch interlock switch are ON.

This is saying the ECM can't verify clutch pedal position, because both clutch pedal switches are ON.

The "ASCD cancel switch" (which is also called the clutch pedal position switch) is on the clutch pedal and is closed when the clutch is fully up. This is the switch that turns off the cruise control when we tap the clutch pedal.

As you know, the other clutch pedal switch is closed when the clutch pedal is fully depressed. This is called the "clutch interlock switch"

To test:
• unplug the ASCD cancel switch (this tells ECU that the clutch pedal is not at the top)
• unplug and short out the clutch interlock connector. This tells the BCM that the clutch pedal is at the floor.
• make sure the car is in neutral and/or press the clutch down
• try to start the car.

I had a similar issue on a Mazda 3 and the fix was to replace the switch... What was VERY interesting is that the switch was made by Nissan!

I don't know if I mentioned it before, but I've done that test as well. I hit the start button without touching the clutch to turn "acc" power on which will wake up all the computers and let them know it's go time. I then unplug the cruise control switch and left it to simulate the clutch pedal leaving breaking the circuit. And finally, I unplugged the clutch interlock switch and jumped it. No change. I then used the start button to cycle power a few times as I heard rumors of there being a time limit between all of the switches opening and closing. Still nothing.

Crap!! I was hoping for better news.

The next step is to view what the BCM "sees" for the clutch pedal position.
Luckily, this doesn't require a Consult III+, but just a a cheap OBD scanner ($20), OBD Fusion ($7-14) and their $14 OEM Diagnostic add on.

With this app, you can connect to the BCM and view the clutch pedal switch status. You have checked the switches, BUT that doesn't mean the BCM sees the required criteria to crank/start the engine.

Here is a screen shot from my G37 Sport (6 speed manual) with the clutch pedal on the floor and fully released.

http://www.the370z.com/attachment.ph...1&d=1620773979

Any interest in pursuing this?

I need to check my setup up to see about the cruise control, but I have done that test with the clutch interlock. Using a laptop and the tuning software, I can watch the clutch switch being toggled in real time. So as far as the clutch interlock is concerned, the ECU and BCM both see that the switch is working as intended, which is part of my previous thoughts about the DTC being thrown actually being a generic error.

I'll report back when I check out the cruise control switch through OBD. I don't know if the app I'm using or the tuning software I have tracks that. If not, I'll look into the app that you have.

Well, car is still an expensive but useless hunk of metal and plastic.

Verified that the both clutch switches (interlock and cruise control) toggle as expected through tuning software.

Also verified that the U1000 and B26E8 codes keep returning after resetting ECU while I was in there.

I tried different variations of unplugging the cruise control switch and jumping the clutch interlock. No change as expected.

The HVAC U1000 CAN Bus code shouldn't prevent the car from being started, worst case no A/C.

What is your next step?

At this point, probably sell the car for scrap metal.

I do have suspicion that the BCM is at fault. But not only do I not wish to pay for a new one, I would have to take the whole car to Nissan (three hours away) to have the new BCM rekeyed or to get a new sets of FOBs to match the new BCM. The only logical thing I can think of is the tuning upset something inside of the BCM which is causing the BCM to stick in a "no start" condition, though nothing about this problem has been logical so far.

Ha. Even according to the actual Nissan techs, there is "nothing wrong" with the car. They used their fancy pants Nissan only computers and allegedly there is nothing wrong with any part of the car. It just doesn't turn over. Because that makes sense. They offered to start swapping out the car piece by piece starting with the IPDM for a low cost of $2.2k for the fuse box alone, not including labor, diagnostics, etc. Instead, they spliced into the IPDM to bypass the entirety of the start circuit using a toggle switch. So you can start the car and it seems to run (mostly, see below) fine now. I have since ordered another IPDM (this is the third one, including the original) and again, no change. The only thing left is to literally swap every single computer (ECO, BCM, FOBs, FOB receptacle, etc.) at once to ensure all the IDs and everything match and that still may not even fix the problem. Also after receiving the car from Nissan, the gear indicator on the dash no longer works and you can no longer turn on sport mode/rev matching. Again, no trouble codes, no blown fuse, no anything "wrong" or "broken" with the car according to me or Nissan. I am beyond over this car.

Go back to the stock tune.

Done. Multiple times. No change. Different ECUs, stock and new tune. No change.

In my opinion, this is a hint. S-mode requires the following inputs to be good:
• cam/crank signals
• clutch pedal / clutch interlock
• gear lever position sensor
• Input shaft speed sensor from transmission
• vehicle speed from gauge cluster

I would verify and/or re-verify those signals.

If I understand the starting circuit as well as I think I do, once the Starter Relay gets the signal from the BCM and actuates the issue must be on the IPDM E/R.

So replacing/troubleshooting the IPDM E/R seems like a logical step to me.

M/T : System Description INFOID:0000000011735111
• When the clutch interlock switch is turned ON, power is supplied to starter relay and starter control relay.
And BCM and IPDM E/R (CPU) detect clutch interlock switch condition by the inputted signal.
• When starter operating condition is satisfied, IPDM E/R turns starter control relay ON by starter control relay
control signal.
• When engine cranking condition is satisfied, BCM turns starter relay ON by starter relay control signal.
• Then battery power is supplied to starter motor (“S” terminal) through starter control relay and starter relay.
And IPDM E/R (CPU) detect starter relay condition by the inputted signal.

Since you have mentioned that you have B26E8 I would suggest triple-checking that.

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