Hey everyone.
I have a 2000 Blazer. 4.3. LT Trim. I have access too ALLDATA's DIY manufacturer service manuals for my car, as well as this TECH2WIN software from VXDIAG that i purchased on amazon.
290k miles

Let me start from the beginning...

filled up on gas at the gas station.

while cruising down the road at around 30mph:
Battery Light turned steady on.
Security Light turned steady on.
Fuel Gauge, Engine Temp gauge, Oil pressure Gauge, and Battery Voltage stopped working.
MPH and RPM gauge continued to work ok.

drove straight home about 30 miles away (thankfully made it home). took about an hour with traffic.
parked the car
about an hour later, i attempted to start the car
car started fine. no issues. all guages work, no lights on instrument cluster were illuminated

next morning,
attempted to start car
car would start, run for barely 2 seconds and shut off. i did this about 3 times before i gave up.
all 3 times, same thing happened. it would crank, start, idle for maybe 2 seconds. then shut off.

checked Battery voltage: 12.5 (i assumed it was good since it would actually crank and start but i checked anyway)
Fuel Pressure: Checked Schrader valve and fuel did shoot out. connected a Fuel pressure gauge and it was at about 55PSI when primed, and it would shoot up to 60 after it attempts to run...... then dies......
pressure heald steady at around 50 after it dies
Security Light Steady on

Did some research based on the symptom and found that this issue might be tied to the Security system/PASSLOCK2

without doing any further research after that, i said screw it, and went with the "throw parts at it" method
replaced ignition switch
replaced ignition lock cylinder (moved the pins to the new lock cylinder so i could use my same old key i used for the doors).
attempted to start the car - SAME ISSUE. Car starts, then dies after 2 seconds.

i said screw it again, and decided to do the resistor method to bypass the passlock sensor thats embeded in the ignition lock housing
yellow wire (5v) -> 2.2k ohm resistor -> spliced into the brown/black wire which is the passlock sensor wire that goes to BCM.
performed passlock key relearn procedure below:
step 1 - 6, i waiting until flashing security light turned off. about 10 to 11 minutes.
step 7, light remained steady on and does not turn off, i even waited about 30 minutes, and it never turned off

attempted to perform the relearn again
step 7, light remained stead on, but i turned it off after 30 seconds (set a timer on my phone)

still. no start

decided to plug in my VXDIAG tech2win scanner with my laptop and noticed something weird.
i CANT pull DTCs from the PCM. Failure to communicate. Tried again with my cheap BOSCH OBD2 scanner - same thing. failure to communicate
i checked the 2 ECM fuses under the hood and they dont appear to be blown. Continuity between the 2 prongs on the fuses are ok. tested with multimeter.

I CAN pull DTCs from the BCM.
i have a U1255 which i cant find much info on. CLASS 2 Communication Malfunction

I can also view the security data on the BCM
PASSLOCK STATE: Monitor Passlock
VCM/PCM FAIL ENABLE: NO
VTD FUEL DISALE: INACTIVE
VCM/PCM FUEL CONTINUE: NO

again. tried the relearn but still. wont work.

i. am. stumped.
could both PCM and/or BCM be bad? she is 22 years old. the BCM and PCM are original so im thinking they could be failing.
has anybody here ever replaced either/both without going to the dealership?

any help would be greatly appreciated!

 

UPDATE

i found this in ALLDATA DIY, which makes me wonder if i'm going about this all wrong.
I'm looking at:
VCM/PCM Fuel Continue: The scan tool displays the state of the VCM/PCM fuel continue mode. The scan tool displays YES when the Passlock(TM) system verifies a valid password to the BCM.
Passlock(TM) Code: The scan tool displays the validity of the Passlock(TM) code received by the BCM. The scan tool displays OPEN, SHORTED, TAMPER and a valid code as a numeric value (1-10).

when i scan my BCM with TECH2WIN, the value for VCM/PCM Fuel Continue is no.
i can change the PASSLOCK code from 'Valid Code 1' to 'Valid Code 10' depending on the resistor size that i splice from the yellow 5v wire near the ignition into the brown/black signal wire.

im wondering if it has to do with the correct Valid Code # telling the VCM/PCM Fuel Continue to yes.
but since my scanner cant read DTCs from the PCM, it got me wondering, does the VTD disable the PCM which is why i cant read the DTCs from the PCM?
is my BCM trying to tell my PCM to enable fuel, but power to PCM is bad?

yesterday, i tested for continuity between the PCM, BCM, SP201 splice pack, and the DLC (obd2 port) and continuity is good. I'm gonna try and check for any shorts when i have the chance.

any input is appreciated from yall

​​​​​​​Thanks!

 

Forget the scanner right now and figure out which is causing the engine to die once it starts. fuel pressure low (gauge), injectors stop pulsing (noid light), or ignition stops (spark jumping gap). Then we can point you in the proper direction.

 

roger.

Quote:

Originally Posted by genocide

Fuel Pressure: Checked Schrader valve and fuel did shoot out. connected a Fuel pressure gauge and it was at about 55PSI when primed, and it would shoot up to 60 after it attempts to run...... then dies......

i failed to mentioned it held pressure for over 10 minutes after engine dies.

injectors stop pulsing (noid light) - how would i go about testing this?

Ignition stops (spark jumping gap) - could you elaborate on this? i did check if spark is making it from the ignition control module to the distributor. spark between those 2 parts looks good. i disconnected the wire at the distrbutor and held it to a bare metal surface and saw the spark jump from the wire to the bare metal surface.. should i check the distributor cap, wires, and plugs? i can check anyway. I just feel like the issue really has to do with my vcm/pcm considering i cant even pull DTCs from it, and the fact that my security light was the first sign that lead me to think its a security issue. buuuut. ya know, if i was positive i wouldnt be here asking for help. thank you!

 

if security problem, injectors go disabled right after vehicle starts. You can see this with a noid light in the injector harness in place of an injector. This is better than guessing. But I worry that you now have the Passlock system screwed up with resistors and such. This might be a second issue you have now introduced, but I have no way of knowing. My personal opinion is that you have about a 1% chance of the PCM being bad.

You must have spark when cranking but what about as it dies? Way you are checking is fine. Same for fuel pressure - what is it KOEO (during after pulse) or when cranking, or when it dies? What pressure does it hold? Need the numbers and detail please. If its the PCM we will get to it. Humor me please.

 

I just found where you already answered about the fuel pressure. So no need to repeat that

 

roger.

Injectors - i'll try and pickup the NOID light. probably within the next few days and let you know the results from that.
Passlock - can the resistors screw the passlock system? doesnt the halleffect sensor in the ignition lock housing introduce resistance the same way a resistor does?
Spark - I'll check how spark is as it dies
Fuel pressure - i'll get more details and accurate numbers

i wont be able to get to furthe diag for another few days with work and all. but i shall let you know
appreciate your response and time

 

Great! We will be here when you return. Until then.. I'll see if I can find the description on exactly how the Passlock system works. I can say with confidence that a hall effect sensor is not a resistor. I think the resistor trick is kind of like trying to fool the PCM into thinking it has a cat converter on the vehicle by using a spark plug non-fouler on the post cat O2 sensor. Actual experiences seem to vary a lot.

I once bought some Passlock resistors off Ebay as a backup for fixing a friend's brothers passlock system (they had replaced the ignition switch assembly and could not get it started - car 75 miles away from me), but when I got there I found they had just failed to do the programming correctly because the battery in the vehicle was near dead - I never attempted to install a resistor. I'll give you the factory info and you can decide for yourself.

 

Here you go - see attachments.