My simple code reader connected to this car in the past but not with the current problem "Cranks but NO Start".
(I've tried the PASSLOCK reset procedure many times with no success.)
The code reader gets a KWP2000 communication error.
I'm trying to decide if I need to replace the BCM or the PCM.
(At $250 for a manufactured PCM I'm reluctant, without strong indication it will fix the problem.)
Can't quickly find a schematic that shows connection to the PCM or the BCM.

Do you mean you are unable to successfully reset pass lock or you can successfully reset passlock but the car won't start?

Tried many time but no success. Each time it ends the same "Cranks but NO Start".
No fuel pump sound, no Fuel gauge movement, no connection to code scanner, NO try to start...

Forget about whether the car starts for answering my 1st question below.

When you go through the passlock relearn procedure, does the security light behave the way it is supposed to after each 10 minute section? Does the security light go out after each 10 minute section of the procedure?

I am trying to ascertain whether the procedure itself is succeeding or failing. If passlock remains triggered, the vehicle will not start. If you cannot successfully relearn passlock and the security light just stays on the whole time, either you are executing a step incorrectly (not trying to insult your intelligence but if you do not follow what the word for a word it does not work) or you have bigger problems.

Based on the above, does the passlock reset behave as expected and turn out the security light at the end of the process?

Separate question. Regardless of the answer to the first question, what is the security light doing when you are cranking the vehicle after having done the passlock reset procedures? Flashing, solid on? Off? This is after the bulb check from turning the key, when you are actually cranking.

Here is the procedure straight from GM.

​​​​​​Do not remove the key from the ignition cylinder at any time during the process. The BCM needs to see at the entire time.

Do not confuse accessory with off when turning to the off position. Do not remove the key in the off position.

Basically if it doesn't say it in the procedure, literally don't do it.

The above are the most common mistakes people make when trying to execute the procedure.

Also I advise hooking your vehicles battery via jumper cables to a vehicle that will be running the entire time or charger as your vehicle will be in the on position for half an hour and if your battery drains too far, not only will the procedure not work but you'll end up with a dead battery and be even more pissed off than you are now.

Personally I have seen passlock sends a lot of vehicles to the wrecking yard because people do not want to pay to replace the BCM. Remember however that there is a pass lock sensor in the ignition switch, so the BCM is not always the culprit. If it doesn't see what it's looking for from the ignition switch sensor, then you cannot expect the BCM to pass on the all clear to the PCM.

I don't know that I've ever seen the BCM directly mess up the OBD2 port. I suspect there is something wrong with one of the can networks. Oh wait, this car doesn't have can so it would be the serial II communications Network. Since you have something at the pins required, the thing is not dead. It is just not talking properly. Again the schematics are needed to figure out where and how it attaches to what in order to sort this out.

MAY have a generalized 3rd generation PCM
BCM diagram but I have to look for it later. I'll try to decipher it and get back to you.

If you haven't figured out yet I have no attention span and I think logically yet highly non linearly.
I am what I am

Diag Port

Please pull the" BODY" fuse from the vehicle and check with a multimeter.

Also pull and check the BCM and PCM fuses and check.

Also, sometimes there can be just enough corrosion on the fuse terminals or the contacts where they plug in to inhibit good contact. Spray the fuse terminals with electrical contact cleaner and repeatedly insert and remove the fuse to sweep off any corrosion.

Also, are you sure your reader is set to protocol Auto detect?

No start:

Please forgive me.
You had already provided the detailed information I have requested immediately above regarding the security light behavior. Since the light is not going out after 10 minutes on any of the attempted relearn procedure attempts, relearn procedure is obviously not succeeding.

You stated you had a worn key and a more recent key. Was the recent key cut from the VIN or was it a copy cut of the old key? Also, was the correct blank used so that the resistor internal to the key is the right one? Without that resistor matching what the ignition expects to see, that he will not start the car.

So now we are down to either of the ignition switch sensor, the key itself, or the BCM.

Are there any other funny things going on like the dash displaying bogus values on the odometer, all of the idiot lights lighting up while driving before all this happened? Door locks acting possessed?

My understanding is that when pass lock is activated, the fuel injectors are disabled but the fuel pump itself is not. Or shall I say more accurately that a default state of injectors disabled is the norm, and a constant checking of the ignition switch sensor confirms to the PCM it is the right key, after which it tells the PCM to uninhibit the fuel injectors.

Have you tried any starting fluid at the intake? Just to see if it fires or if it runs until out of starting fluid?

I do not have the diagram I mentioned above. I looked at this morning.

Any developments?

This has been a long and difficult journey. And not yet finished. But here is an update.

Decided to buy a rebuilt PCM/ECM from Flag Ship 1 "FS1" (I've used them before - great results)
New PCM corrected the "No Start" problem but resulted in a new set of symptoms. Now I get a P1635 (+5 Reference circuit) that will not clear.

Also, occasionally P0327 (Knock Sensor 1 Circuit Low). I've checked the wiring from the PCM to the knock sensor connector, no problem. Tried the AC voltage test on the knock sensor and only get small AC voltage spikes with a DVM. Ordered replacement sensor - I will report on results once instaled.

The "P1635 +5 volt circuit" remains a mystery. FS1 took back the PCM and verified +5 output pins were working correctly (as well as the Knock circuit). Since PCM was returned both the codes remain (P1635 and P0327). I have checked 3 of the 4 sensors that should receive +5V, with no problems. I have not yet checked the Inlet Air Temp Sensor. I just learned it also uses +5V. I'll report on that last +5V circuit soon.

I do not expect a problem with the IAT +5V and don't expect the knock sensor to be +5V related -
so looking for suggestion on where to look next on the +5V Code.

Thanks in advance,
Larry

What is the measured voltage at these 5V reg signal points with key in ON position?

Did they VIN match the PCM to your car when they programmed it?

What schematic are you working off of to indicate that these are the only 4 "devices" that use the 5V ref line? I'm not challenging the validity of the statement, I'm simply trying to ascertain what your data source is before I try to investigate on my end.