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Discussion Starter · #1 · (Edited)
Good afternoon and thanks for taking the time to read my message today!
I am a long time reader, first time poster so.. here goes!

2005 Chevy Trailblazer

  • Occasional issue with Passlock symbol coming on dash, car not starting..
  • Bought a Passlock bypass unit and installed by the BCM
  • Bypass works great... except car still doesn't start sometimes and wasn't getting any power to the BCM / Bypass Module when this occurs..
  • Figured out no power was being sent back there
  • Figured out that if I remove the negative battery cable from car battery, wait a moment, and put it back on.. power starts flowing back there to the BCM & Bypass Module and car starts right up after doing this
(During the time that there is no power for the BCM / Bypass unit, also getting no power to the radio (unless its already turned on), interior lights, headlights (unless turned on manually), front windshield wipers, power door locks/unlock, and power window switches)

Reached out to support team of the bypass module and explained to them this trick of resetting the battery and they said the problem is not with the passlock or the bypass unit, but rather a "Power Distribution Issue"

I am thinking I will just bring it to the shop, as I have been dealing with this whole problem and making it work for over a year now... I'd be fine using the car in it's condition but I am having trouble getting a State Inspection done due to computer being reset all the time..
I always thought it was my modest electrician work with installing the bypass unit....hell I guess I've had it right this whole time lol.

Checked fuses under the hood and all seemed good... Do I need a new fuse box? Any advice on where this power that goes to the BCM comes from? What should I tell the mechanic? Just explain like I did here?

Thanks all!
Have a great day!
 

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2002 chevy trailblazer_lt
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Good afternoon and thanks for taking the time to read my message today!
I am a long time reader, first time poster so.. here goes!

2005 Chevy Trailblazer

  • Occasional issue with Passlock symbol coming on dash, car not starting..
  • Bought a Passlock bypass unit and installed by the BCM
  • Bypass works great... except car still doesn't start sometimes and wasn't getting any power to the BCM / Bypass Module when this occurs..
  • Figured out no power was being sent back there
  • Figured out that if I remove the negative battery cable from car battery, wait a moment, and put it back on.. power starts flowing back there to the BCM & Bypass Module and car starts right up after doing this
(During the time that there is no power for the BCM / Bypass unit, also getting no power to the radio (unless its already turned on), interior lights, headlights (unless turned on manually), front windshield wipers, power door locks/unlock, and power window switches)

Reached out to support team of the bypass module and explained to them this trick of resetting the battery and they said the problem is not with the passlock or the bypass unit, but rather a "Power Distribution Issue"

I am thinking I will just bring it to the shop, as I have been dealing with this whole problem and making it work for over a year now... I'd be fine using the car in it's condition but I am having trouble getting a State Inspection done due to computer being reset all the time..
I always thought it was my modest electrician work with installing the bypass unit....hell I guess I've had it right this whole time lol.

Checked fuses under the hood and all seemed good... Do I need a new fuse box? Any advice on where this power that goes to the BCM comes from? What should I tell the mechanic? Just explain like I did here?

Thanks all!
Have a great day!

There are many power lines to the BCM. Some are for the operation of the BCM itself, some are merely signals to the BCM so it knows the current key position, some are for powering devices the BCM operates, some are on all the time, some are on in accessory key position, some are on in the RUN key position, and so on, and so on.

57267
 

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Discussion Starter · #3 ·
There are many power lines to the BCM. Some are for the operation of the BCM itself, some are merely signals to the BCM so it knows the current key position, some are for powering devices the BCM operates, some are on all the time, some are on in accessory key position, some are on in the RUN key position, and so on, and so on.

View attachment 57267
Well I had given in for a moment but now I am back!
Thank you @TJBaker for your reply and provided diagram.

The wire in question is the red/white "12VREF" wire going into Pin E9 to the Anti Theft System. During the times that the passlock light is enabled on the dash and the car won't start - I am getting no power through this wire checking it near the BCM. When the car does start I get power through this wire. I feel like I need to trace this wire back to the source? Is there any electrical diagram to help with this? I am having trouble locating electrical diagrams. I picked up a Haynes Repair Manual which has a "Starting and charging systems" diagram with some information but I can't seem to find the BCM on this diagram. I will check the starter relay this weekend just to make sure. Any additional advice is immensely appreciated. Thanks again.

Rectangle Schematic Font Slope Parallel




Additional thoughts after studying your provided diagram a bit further..

Trying to learn how to / make sure I am reading the diagram you provided.

So, from what I think I understand is:

1. Power from the battery goes into the under the hood fuse box
2. TBC 1 FUSE 31 10A Fuse is provided power which goes to the BCM via the ORG (Orange?) wire.
3. This powers the BCM.
4. BCM Sends power out of Pin E9 via "12V REF" Red/White wire -> to the Anti-Theft System?

Is this right? This whole time I was just assuming power was going into the BCM using that red/white wire. Or is it the other way around.. Sorry for my low level understanding of these electronics.
 

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Additional thoughts after studying your provided diagram a bit further..

Trying to learn how to / make sure I am reading the diagram you provided.

So, from what I think I understand is:

1. Power from the battery goes into the under the hood fuse box
2. TBC 1 FUSE 31 10A Fuse is provided power which goes to the BCM via the ORG (Orange?) wire.
3. This powers the BCM.
4. BCM Sends power out of Pin E9 via "12V REF" Red/White wire -> to the Anti-Theft System?

Is this right? This whole time I was just assuming power was going into the BCM using that red/white wire. Or is it the other way around.. Sorry for my low level understanding of these electronics.

You're doing well so far!

Yes, the BCM is powered by the orange wire at connector 1, pin A3. But the BCM also has power coming in to several other places as shown in the diagram. The trouble is that GM does not provide detailed information as to which power wire does what functions. I do know that the power for the Passlock sensor from the BCM does come from that orange wire.

With the other systems you mentioned not working I would suspect there is an issue with the power coming in on the orange wire to the BCM. Most things like the radio for example have power ALWAYS, even with no key. It is the BCM that tells them to wake up and turn on. So if the BCM doesn't get that power on the orange wire all sorts of things won't work. It won't crank, the radio won't turn on and so on. So when it fails to start check for power at that orange wire to the BCM.




Here is some information on how the Passlock system works.... and a video I made some time ago while fiddling with Passlock sensors...

So the Passlock sensor is a small circuit up in the key/lock assembly. As I think you figured out now the red/white wire (Connector 2, pin E9) supplies the 12 volts from the BCM to the Passlock sensor circuit to power that device. The black wire (connector 2, pin E8)
(sometimes orange/black) supplies the ground.

The yellow wire (Connector 1, pin 10) get 5 volts from the BCM and when the key is turned to CRANK, the Passlock sensor is activated by a small magnet in the lock cylinder and the circuit shorts a small resistor between the yellow wire and ground. This drops the 5 volt signal down some, but not all the way to zero. The BCM reads what the voltage is and if it matches the value the BCM has stored then you are good to go. If it doesn't match you don't crank.

 
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