2005 TrailBlazer Power Distribution issue...

3143 Views 22 Replies 4 Participants Last post by jsusnaim, May 4, 2022

wontonstrips

Discussion Starter · Jun 26, 2021 (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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TJBaker

· #2 · Jun 26, 2021

wontonstrips said:
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.

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wontonstrips

Discussion Starter · #3 · Jul 11, 2021

TJBaker said:
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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TJBaker

· #4 · Jul 12, 2021

wontonstrips said:
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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wontonstrips

Discussion Starter · #5 · Nov 18, 2021 (Edited)

TJBaker said:
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.

Well it’s been a while and I am finally finding the time to get back at it. I am slowly learning more and more about DC circuits. I will use this post to document my findings as I go in the hopes it may help someone else or someone may chime in to help! Any and all advice is greatly appreciated.

So I managed to get the plastic off around the ignition cylinder in order to check out the passlock sensor connector. Some videos I watched claimed a common problem of the connector having a little too much wiggle room and causing issues from vibrations or weather. I don’t think this is my issue, while the connector can wiggle a tiny bit, wiggling it while the car was on didn’t seem to cause any changes.

Motor vehicle Bumper Gas Electrical wiring Machine

Speedometer Light Gauge Trip computer Tachometer

Now I am moving on to checking power going into the BCM via orange wire from TBC 1 Fuse #31 -> BCM connector C1 Pin A3.

I also will check power leaving the BCM on red/white wire going to the ignition from BCM connector C2 Pin E9.

I pulled out every fuse and they all look good. I did a resistance check on a few fuses that seemed relevant and also checked resistance on the circuit breakers.. everything seemed to check out. EDIT: Also I checked the Starter relay and a couple other relays out with just a resistance check between the 86 and 85. I don't have a spare battery to hook them up to really check them out but i think they are OK.

Here is my plan:
Troubleshooting #1
Check continuity of orange wire powering BCM
1. Disconnect car battery
2. Cut orange wire before it enters into BCM at C1 Pin A3.
4. Set multimeter to 200 ohms
5. Connect one lead to ground
6. Connect other lead to orange wire
Should be less than 5 ohms of resistance

Troubleshooting #2
Check ground of Black wire leaving BCM
1. Disconnect car battery
2. Cut black wire after it leaves BCM at connector C2 Pin E8.
3. Set multimeter to 200 ohms
4. Connect one lead to ground
5. Connect other lead to black wire thats going to ground
Should be less than 5 ohms

Troubleshooting #3
Check continuity of red/white wire leaving the BCM -> Ignition/passlock sensor
1. Disconnect car battery
2. Cut red/white wire after it leaves BCM at connect C2 Pin E9
3. Set multimeter to 200 ohms
4. Connect one lead to ground
5. Connect other lead to red/white wire that supplies power to ignition/passlock sensor.
Should be less than 5 ohms

QUESTIONS
1. Where does the BCM ground out to and/or can I check resistance through the BCM? Meaning if I disconnect car battery and set multimeter to 200 ohms, put one lead to a good ground and the other lead to the orange wire going into the BCM, can i check the resistance of this wire going into the BCM and then eventually to ground or will this mess up the BCM?

Also I drew up a diagram of the Bypass Module I installed and relevant circuit. Also the directions I was given for the install of the bypass mod.. Hopefully I got it all right.

Rectangle Font Parallel Number Screenshot

Rectangle Font Line Parallel Laptop

Thank you!

EDIT: Curiosity I have noticed on very rare occasions... I will be driving down the road listening to music and the music will suddenly slow down for a few seconds.. then jump back up to normal speed. I'm curious if this is a voltage thing to the radio? This is by no means a regular occurrence but i have noticed it happen maybe 3-5 times over the year. I drive my vehicle nearly every day. Thought I should include this as a honorable mention considering I may be having some type of power issue.

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TJBaker

· #6 · Nov 18, 2021

There appears to be a discrepancy between your written instructions and the hand drawn schematic. In the latter you show terminal C2, E8 and the brown wire from the bypass module going to ground, but in the connection directions no mention of a ground connection exists for these two wires. Factory wiring for C2,E8 is to the low reference terminal of the Passlock sensor. A low reference is not the same as a ground. It is close, but not equal.

wontonstrips

Discussion Starter · #7 · Nov 18, 2021

TJBaker said:
There appears to be a discrepancy between your written instructions and the hand drawn schematic. In the latter you show terminal C2, E8 and the brown wire from the bypass module going to ground, but in the connection directions no mention of a ground connection exists for these two wires. Factory wiring for C2,E8 is to the low reference terminal of the Passlock sensor. A low reference is not the same as a ground. It is close, but not equal.

Ah, I simply assumed the black wire from C2 E8 went to ground from one of your last posts. That's why I did draw it that way

TJBaker said:
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.

wontonstrips

Discussion Starter · #8 · Nov 18, 2021

Now I am wondering.. the passlock sensor has 3 wires, a yellow (disconnected), a orange/black, and the red/white. I believe the red/white is the 12V ref discussed from C2 Pin E9 but is that orange/black the one you are talking about? It is only black coming out of the BCM

TJBaker

· #9 · Nov 18, 2021

wontonstrips said:
Well it’s been a while and I am finally finding the time to get back at it. I am slowly learning more and more about DC circuits. I will use this post to document my findings as I go in the hopes it may help someone else or someone may chime in to help! Any and all advice is greatly appreciated.

So I managed to get the plastic off around the ignition cylinder in order to check out the passlock sensor connector. Some videos I watched claimed a common problem of the connector having a little too much wiggle room and causing issues from vibrations or weather. I don’t think this is my issue, while the connector can wiggle a tiny bit, wiggling it while the car was on didn’t seem to cause any changes.

View attachment 58333 View attachment 58334

Now I am moving on to checking power going into the BCM via orange wire from TBC 1 Fuse #31 -> BCM connector C1 Pin A3.

I also will check power leaving the BCM on red/white wire going to the ignition from BCM connector C2 Pin E9.

I pulled out every fuse and they all look good. I did a resistance check on a few fuses that seemed relevant and also checked resistance on the circuit breakers.. everything seemed to check out. EDIT: Also I checked the Starter relay and a couple other relays out with just a resistance check between the 86 and 85. I don't have a spare battery to hook them up to really check them out but i think they are OK.

Here is my plan:
Troubleshooting #1
Check continuity of orange wire powering BCM
1. Disconnect car battery
2. Cut orange wire before it enters into BCM at C1 Pin A3.
4. Set multimeter to 200 ohms
5. Connect one lead to ground
6. Connect other lead to orange wire
Should be less than 5 ohms of resistance

Troubleshooting #2
Check ground of Black wire leaving BCM
1. Disconnect car battery
2. Cut black wire after it leaves BCM at connector C2 Pin E8.
3. Set multimeter to 200 ohms
4. Connect one lead to ground
5. Connect other lead to black wire thats going to ground
Should be less than 5 ohms

Troubleshooting #3
Check continuity of red/white wire leaving the BCM -> Ignition/passlock sensor
1. Disconnect car battery
2. Cut red/white wire after it leaves BCM at connect C2 Pin E9
3. Set multimeter to 200 ohms
4. Connect one lead to ground
5. Connect other lead to red/white wire that supplies power to ignition/passlock sensor.
Should be less than 5 ohms

QUESTIONS
1. Where does the BCM ground out to and/or can I check resistance through the BCM? Meaning if I disconnect car battery and set multimeter to 200 ohms, put one lead to a good ground and the other lead to the orange wire going into the BCM, can i check the resistance of this wire going into the BCM and then eventually to ground or will this mess up the BCM?

Also I drew up a diagram of the Bypass Module I installed and relevant circuit. Also the directions I was given for the install of the bypass mod.. Hopefully I got it all right.

View attachment 58337

View attachment 58336

Thank you!

EDIT: Curiosity I have noticed on very rare occasions... I will be driving down the road listening to music and the music will suddenly slow down for a few seconds.. then jump back up to normal speed. I'm curious if this is a voltage thing to the radio? This is by no means a regular occurrence but i have noticed it happen maybe 3-5 times over the year. I drive my vehicle nearly every day. Thought I should include this as a honorable mention considering I may be having some type of power issue.

Re:Troubleshooting 1, 2 & 3: Don't cut any wires! That only leads to more questionable connections at the point where you have to re-establish the connections.

Troubleshooting #1: the orange wire is connected through a fuse to battery positive. Trying to read resistance of this to ground may very well fry your meter. The only thing you need to check at the orange wire is that you have a reliable 12 volts positive at all times. It should read whatever your battery voltage is.

Troubleshooting#2: you can check the ground by simply disconnecting the connectors from the BCM and then gently probe the appropriate terminal to read resistance to ground.

Troubleshooting#3: you can simply measure the voltage at the red/white wire at the Passlock sensor.

As for checking the resistance through the BCM C1, A3 to ground, again you can just disconnect the harness connector(s) and then connect black test meter lead to chassis ground and probe the proper terminal on the BCM. Should read somewhere in the neighborhood of 175 thousand ohms.

Best practices are to first disconnect the battery before disconnecting any modules harnesses.

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TJBaker

· #10 · Nov 18, 2021

wontonstrips said:
Ah, I simply assumed the black wire from C2 E8 went to ground from one of your last posts. That's why I did draw it that way

True enough! Depending on the scope of what I am posting I have at times used ground & low reference interchangeably.

I believe it works like this: for circuits that the BCM (or other control module) wants to monitor,, the 'ground' side of said circuit runs through some circuitry inside the module instead of simply connecting to chassis ground. In this way the module can monitor the state of that ground wire and detect things like a broken wire.

chem_man

· #11 · Nov 18, 2021

wontonstrips, you need to get yourself a set of the following - they make back probing easy! I wish I had purchased them years ago!!!

Amazon.com: Bionso 25-Piece Multimeter Leads Kit, Professional and Upgraded Test Leads Set with Replaceable Gold-Plated Multimeter Probes, Alligator Clips, Test Hooks and Back Probe Pins. : Industrial & Scientific

Buy Bionso 25-Piece Multimeter Leads Kit, Professional and Upgraded Test Leads Set with Replaceable Gold-Plated Multimeter Probes, Alligator Clips, Test Hooks and Back Probe Pins.: Test Probes & Leads - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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or

www.amazon.com

Goupchn Back Probe Kit 20PCS Banana Plug to Copper Alligator Clip Automotive Test Leads Set with 3 Configurations Back Probe Pins for Car Repairing Diagnostic 5 Colors: Amazon.com: Industrial & Scientific

Goupchn Back Probe Kit 20PCS Banana Plug to Copper Alligator Clip Automotive Test Leads Set with 3 Configurations Back Probe Pins for Car Repairing Diagnostic 5 Colors: Amazon.com: Industrial & Scientific

www.amazon.com

Good Luck!

TJBaker

· #12 · Nov 18, 2021

wontonstrips said:
Now I am wondering.. the passlock sensor has 3 wires, a yellow (disconnected), a orange/black, and the red/white. I believe the red/white is the 12V ref discussed from C2 Pin E9 but is that orange/black the one you are talking about? It is only black coming out of the BCM

I think the color changes somewhere along the way.

Rectangle Font Slope Parallel Schematic

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wontonstrips

Discussion Starter · #13 · Nov 18, 2021

TJBaker said:
Re:Troubleshooting 1, 2 & 3: Don't cut any wires! That only leads to more questionable connections at the point where you have to re-establish the connections.

Troubleshooting #1: the orange wire is connected through a fuse to battery positive. Trying to read resistance of this to ground may very well fry your meter. The only thing you need to check at the orange wire is that you have a reliable 12 volts positive at all times. It should read whatever your battery voltage is.

Troubleshooting#2: you can check the ground by simply disconnecting the connectors from the BCM and then gently probe the appropriate terminal to read resistance to ground.

Troubleshooting#3: you can simply measure the voltage at the red/white wire at the Passlock sensor.

As for checking the resistance through the BCM C1, A3 to ground, again you can just disconnect the harness connector(s) and then connect black test meter lead to chassis ground and probe the proper terminal on the BCM. Should read somewhere in the neighborhood of 175 thousand ohms.

Best practices are to first disconnect the battery before disconnecting any modules harnesses.

Man probing the connector terminals instead of cutting the wire LOL why didn’t i think of that!! Glad I decided to post here. Seems I have a little more research to do. Was pretty tired when I posted last night just wanted to get a thoughts/plan down on paper.

I picked up a test lamp so if I remove connector C1 and ground my test lamp I can probe the A3 pin coming from the fusebox thru the test lamp connected to ground?

Can I also do this with my multimeter set to DC Volts?

wontonstrips

Discussion Starter · #14 · Nov 18, 2021

t

chem_man said:
wontonstrips, you need to get yourself a set of the following - they make back probing easy! I wish I had purchased them years ago!!!

Amazon.com: Bionso 25-Piece Multimeter Leads Kit, Professional and Upgraded Test Leads Set with Replaceable Gold-Plated Multimeter Probes, Alligator Clips, Test Hooks and Back Probe Pins. : Industrial & Scientific

Buy Bionso 25-Piece Multimeter Leads Kit, Professional and Upgraded Test Leads Set with Replaceable Gold-Plated Multimeter Probes, Alligator Clips, Test Hooks and Back Probe Pins.: Test Probes & Leads - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

or

Goupchn Back Probe Kit 20PCS Banana Plug to Copper Alligator Clip Automotive Test Leads Set with 3 Configurations Back Probe Pins for Car Repairing Diagnostic 5 Colors: Amazon.com: Industrial & Scientific

Goupchn Back Probe Kit 20PCS Banana Plug to Copper Alligator Clip Automotive Test Leads Set with 3 Configurations Back Probe Pins for Car Repairing Diagnostic 5 Colors: Amazon.com: Industrial & Scientific

www.amazon.com

Good Luck!

Haha thank you I actually just picked up a set of alligator clip s and a automotive test lamp with a ground connector

TJBaker

· #15 · Nov 19, 2021

wontonstrips said:
Man probing the connector terminals instead of cutting the wire LOL why didn’t i think of that!! Glad I decided to post here. Seems I have a little more research to do. Was pretty tired when I posted last night just wanted to get a thoughts/plan down on paper.

I picked up a test lamp so if I remove connector C1 and ground my test lamp I can probe the A3 pin coming from the fusebox thru the test lamp connected to ground?

Can I also do this with my multimeter set to DC Volts?

I don't own a test light. I am that guy who wants to know if the wire has 12.8 volts vs 12.3 vs 11.9. I don't think a test light will do that.

TJBaker

· #16 · Nov 19, 2021

wontonstrips said:
t

Haha thank you I actually just picked up a set of alligator clip s and a automotive test lamp with a ground connector

A backprobe set is very helpful in probing harness connectors. The thin probes make it much easier than trying to poke a needle or what have you in there.

wontonstrips

Discussion Starter · #17 · Dec 27, 2021

Finally getting around to post... So I did get a set of backprobes and was able to do some tests -
I backprobed the orange wire going into BCM Connector 1, Pin A3 and it had consistent power at all times, even while I was experiencing the problem... So all good there.

I found my problem at the passlock sensor near the ignition.

During the time I am having the problem with the passlock light illuminated on the dash I am getting no power at the red/white wire going into the passlock sensor near ignition.
I suppose this means my issue is with the red/white wire getting power from the BCM but could also be a ground?

Not sure what I will do next but I feel I am getting a little closer to the source of the problem haha. Thanks and happy holidays!

Here's a few pictures from when I was testing.

Image below: 0.00 Volts at passlock sensor - Engine: Off, Key Position: On, Problem: Yes

Speedometer Vehicle Trip computer Odometer Tachometer

Image below: 11.18 Volts at passlock sensor - Engine: Off, Key Position: On, Problem: No

Speedometer Vehicle Tachometer Trip computer Odometer

Image below: 13.08 VDC at passlock sensor - Engine: On, Key Position: On, Problem: No

Speedometer Trip computer Vehicle Tachometer Odometer

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TJBaker

· #18 · Dec 28, 2021

Edited while composing because I saw something while writing a response!!
--------------------------

Not likely a ground since I assume you are testing with the same ground point each time?? A chassis ground?

I would now check for 12 volts at the BCM end of that red/white wire. If you find that at the same time you have power to the BCM and have no power at the Passlock sensor but you do have power at the BCM end of that same wire then clearly there is a bad connection or wire damage somewhere between the two ends.

When you tested for power to the orange wire at the BCM did you use a chassis point for a meter ground or use a BCM terminal for ground? If using a chassis point when testing for power at that orange wire that still leaves the possibility of the BCM having a faulty ground connection you see.

--------------------------

So I was composing a response when something clicked. I looked back at your first image where you have the issue of no Passlock sensor supply voltage. Look at the battery gauge. Does not show a voltage!! That gauge is driven by serial communications from the BCM to the Instrument Cluster. Your BCM is not active in the picture! With the key in any position other than OFF that BCM should be up and running but the lack of a voltage gauge reading at the very minimum suggest the BCM is not awake and operating.

Back at message #2 in this discussion there is an image. On the top there is a power source labelled "TBC Ig Fuse 50 3A", "Hot in ACC, RUN, OR START" . That leads to terminal A18 on connector 3, "Ignition 0 Voltage". This is the power signal that alerts the BCM to awaken and get ready for business. You may have an issue there in that ribbon cable. You can test for voltage at the BCM end of that flat ribbon cable. Here in this image I am probing terminal A11, a ground. You want to test A18 for 12 volts whenever the key is not OFF. In particular, test when the issue is present.

Circuit component Green Automotive lighting Electrical wiring Hardware programmer

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wontonstrips

Discussion Starter · #19 · Dec 28, 2021

First off - Can't express how grateful I am for all of your responses @TJBaker - Thank you!

Yes when testing the passlock sensor I used the same ground each time - chassis ground
When testing the orange wire at BCM I used a chassis ground as well.

Response to your edit:
Yes when the problem is happening the battery gauge goes down to 0.

Sometimes the car starts fine no problems occurring - then while I am driving, bam battery gauge on the instrument cluster falls down to 0, passlock light pops on.
And as I continue driving the battery gauge turns on and off swinging up to 14V and down to 0 along with the voltage on that red/white wire. (and along with the other symptoms.. headlights, interior lighting, backlight on instrument cluster, rear power windows..etc.)

I will look into testing this Connector 3 thank you!!

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TJBaker

· #20 · Dec 28, 2021

While you are there testing for power at C3:A18 it may be wise to test for a good consistent ground at C3:A11. The diagram at post #2 above shows two grounds for the BCM. Yes, there are two wires for ground at connector C3. One is at A11 and the other is at B11. Access is easy to A11 but B11 is not so easily accessed. HOWEVER!!... Internally they are in fact the same as they immediately join the same PCB tracing as seen here...

Passive circuit component Circuit component Resistor Hardware programmer Electronic instrument

So for a quick test one can just check A11 for either continuity to chassis ground or test for power and ground across the large red battery power wire to the rear fuseblock and BCM C3:A11.

One would have to disconnect the flat cable from the BCM if one wished to verify both of the ground wires separately from the BCM flat connector #3 for a proper path to ground.

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