I checked the BCM connectors with just my multimeter and watched for evidence of signal or voltage. Nothing abnormal found but I did see that Connector C3 A10 lists 2 options for RAP relay.. one without. I have no RAP relay to check.. so what is the BCM doing looking for it? Why is it looking now?
After checking the BCM connectors I took a look at the P0102 MAF and found a broken wire at the connector so I repaired it and now the codes present are..
I will do the TDS key relearn today in hopes that changes something.

Because we need to communicate on all of these issues, so I organized them. As of that writing, the codes presented were:

. . . so around 30 codes in nearly-random order inside of and outside of quotes of me spread across two posts.

It is less important what order the codes come out of the scanner, and more important we can all communicate about them to assist with your issue. This distilled list helps us visualize and attack:

B1422 - Opinions vary, but it didn't come back
B1477 - RAP relay open or short to ground
B3102 - Keyless entry data circuit low voltage
B3106 - Keyless entry data circuit issue
B3094 - No response from PCM?
P0102 - MAF sensor circuit low
P1626 - Loss of fuel enable signal
U1016 - Lost communication from PCM to other modules
U1040 - Lost communication from EBCM to other modules
U1064 - Lost communication from BCM to other modules

Analog or digital multimeter?

Yep, it looks like no RAP relay after all. What do you have in this position and this position below?:




I think we're hung up on the RAP relay, while not having answers to the basics:

Step 1: Remove the RAP fuses (I changed it) and try again and see what happens. Maybe step 2 and 3 are unnecessary . . . ?
Step 2: Check all fuses with volt meter set to continuity, test from tip to tip, not test point to test point
Step 3: Check wiring and plugs connecting to the BCM, PCM, and EBCM.[/QUOTE]

Cool! Looks like:
B1422 - Opinions vary, but it didn't come back
B1477 - RAP relay open or short to ground
B3102 - Keyless entry data circuit low voltage
B3106 - Keyless entry data circuit issue
B3094 - No response from PCM?
P0102 - MAF sensor circuit low
P1626 - Loss of fuel enable signal
U1016 - Lost communication from PCM to other modules
U1040 - Lost communication from EBCM to other modules
U1064 - Lost communication from BCM to other modules

. . . which distilled to:
B1477 - RAP relay open or short to ground
P1626 - Loss of fuel enable signal
U1064 - Lost communication from BCM to other modules

If it was a key-relearn issue, it never would have started in this post: https://www.gmforum.com/buick-172/cu...0/#post1652003
If it needed a relearn, it would not have started these three times.

So, to summarize:

1. Remove the RAP fuses and try again and see what happens.
2. Check all fuses with volt meter set to continuity, test from tip to tip, not test point to test point
3. Check wiring and plugs connecting to the BCM, PCM, and EBCM.
4. What is the fuel pressure while the no-start condition is happening?
5. Is there spark at the spark plugs while the no-start condition is happening?
6. Are the injectors injecting while the no-start condition is happening?

I bet you make killer moonshine... Your distillation skills are great.
I checked the BCM connectors with my DVM set to 0.000 and was noting behavior at each pin sequence Key In through Start.
I could have hooked up a scope but I was just looking for signs of activity.
I checked fuses with a test light (both sides
Fuel pressure 55psi at key on drops to 50psi and holds
If I can get vibration probe near enough maybe I can get a waveform capture of the injectors rather than just the signals to be sure sure.. I guess. But I think they are working.
I'll double-check the spark.

LOL

I'm thinking if you are testing on a signal conductor, it might be better to use an analog volt volt meter so you can see the needle move, as opposed to a digital volt meter that might not react quickly enough to signal pulses.

Blade to blade? . . . all 60-ish fuses?

You still have the rest of my list on your list, right?:

1. Remove the RAP fuses and try again and see what happens.
2. Check all fuses with volt meter set to continuity, test from tip to tip, not test point to test point
3. Check wiring and plugs connecting to the BCM, PCM, and EBCM.
4. What is the fuel pressure while the no-start condition is happening?
5. Is there spark at the spark plugs while the no-start condition is happening?
6. Are the injectors injecting while the no-start condition is happening?

Checked during 2 crank cycle second time through the key relearn, and no spark detected.
Completed the relearn second time through and no start.
Looking for spark first before anything else.

I think you're on the right track!

For no particular reason I started with the ignition relay circuit searching for lost spark and thats lead to finding no power at IP panel Crank signal, BCM, Cluster fuse hot side feed supplied from the under hood fuse box IGN 1 30A fuse .. That fuse feeds direct to the ignition key then the IP panel where it is missing.
Ignition switch? Something besides the resistor?

I'll try a tracing signal on the wire from the loom under the column towards the IP panel and see what I find.

I think I have two problems which may or may not be related.
One is no spark. The AllDataDIY EI system diagnostic leads me an "open or short to ground in the IGN 1 voltage circuit" and that ... Is the BCM circuit.


My second problem is no power to IP panel fuse A3-6 and in checking that out grabbed this.

I was checking voltage during KI,KO,and Start on each circuit this was G
F drops out completely during Start.
H looks like this

Ok then.. to continue..H the Run Start circuit looks like this.


Dropping out during start.

Where do you think I should head next to?
i did pull the inadvertent power fuse but no change..

Well I'm still stuck it seems.
To remove the ignition switch from the equation of missing 12v to IP panel fuse A3 (Crank, BCM, Cluster) in Run (it'* present in Start) I replaced it and still no power.
BCM is still putting out the B1477 RAP relay nonsense.
What am I missing?
What can cause the 12v to be present in Start but not Run?
In looking at the lock tumbler and speaking with a locksmith that mechanism has nothing to do with the electrical circuit and that* is all controlled by the Switch/8745 harness. But... rechecking just now with the old key still, I only have 12v with the key at Start on that circuit and the only thing I see that can be a variable is the actual lock/tumbler. Please make it make sense.
Does that key cylinder make electrical contacts that maintain circuit integrity or just makes the switch mechanism move to the selected setting where the internal contacts are engaged?


Also I still have no answer as to why the BCM is looking for the RAP voltage it doesn't have a circuit to.

CONDITIONS FOR SETTING THE DTC - The BCM detects no voltage at the RAP relay control circuit when the BCM has not grounded the circuit.

That seems to say the BCM is grounding the circuit to keep it 'drawn down or on' for the ten minutes before turnings off the lights radio etc. through the inadvertent power fuse (which is why you asked about it?) but that it'* monitoring voltage on a circuit.. some circuit somewhere.. if only.
Deep sigh.