V1 Anti Theft Re-engaged, Blowing ECM fuse and ignition fuse on BCM

[KingChuck24]

With c2 unplugged and the TDM in it blows, with TDM unplugged and c2 in it blows, with both unplugged it also blows. Does this mean its neither of these modules?

 

[Gtstorey]

Does it blow with c4, c2 and tdm unplugged?

 

[KingChuck24]

It does not blow when they are all unplugged. The dash also does not get any power.

 

[Gtstorey]

Plug one in with the others unplugged and try it. Then unplug that one, plug another in and try it. Repeat for the last one. And write it down as you do it so you don’t get confused.

I’m not sure that I’m following exactly what was plugged in when but it seemed like at one point it was blowing caused by two different modules plugged in. It’s doubtful that both modules are blowing a fuse. I think it is probably wiring that is shorting as you plug and unplug modules, but we need to confirm with plugging in one module at a time.

 

[Gtstorey]

This includes testing C4

 

[KingChuck24]

VATS only good
C2 only good
C4 only blows the fuse

 

[Gtstorey]

And the direct to ground measurement (no resistance) on the brown wire goes away when c4 is unplugged?

if so, it would appear that the BCM is bad, however there is a slight chance something that the bcm is powering is shorted and causing the problem. I think the downstream circuits “should” be isolated from causing this, but strange things happen.
But before I bought a BCM, I would inspect the brown and yellow wires all of the way from the switch to the bcm c4 plug.

 

[KingChuck24]

I visually inspected the harness and nothing seemed to be off. However, I did not cut it open. Should I cut it open all of the way from the ignition to the bcm and see if there is anything wrong? Also they all get continuity to there expected pins on the BCM so I am not sure.

In terms of a new BCM I know they are programmed to the car or at least the vin. How would I program in a new BCM?

 

[Gtstorey]

Check for continuity to ground on the wires at the switch with all of the modules unplugged. If not grounded with modules unplugged it’s probably not worth unwrapping the harness. You might try disconnecting all of the connectors on the bcm except the c4 and see if it still shoots the fuse. If it doesn’t it could still be bad, but if it does it eliminates everything down stream on those connectors. Then if you can find the pin out for your c4 connector you can see if it’s a short to ground on the pins directly in the bcm with all connectors unplugged.

I think Ross has swapped bcm without programming, if not you can order them online preprogrammed.

 

[Ross]

Just have to reprogram the key with a new BCM. No software programming required.

 

[Gtstorey]

As another test you could see if the the pins on c4 corresponding to the yellow and brown wires have a short to the case, with all bcm connectors removed. No short doesn’t mean the bcm is good, but a short does prove the bcm is bad.

 

[Gtstorey]

Just have to reprogram the key with a new BCM. No software programming required.

Is that a “new” BCM from GM or a replacement used BCM?

 

[KingChuck24]

With all of the plugs unplugged there is no ground from any of the ignition wires. Not sure what you mean by short to the case, if I had one probe on the ignition wire where would the other one go?

Going to look around for a new BCM tonight.

 

[Ross]

Scrap yard recycled BCM.

 

[Gtstorey]

With all of the plugs unplugged there is no ground from any of the ignition wires. Not sure what you mean by short to the case, if I had one probe on the ignition wire where would the other one go?

Going to look around for a new BCM tonight.

Other probe would go against the metal case of the bcm. The other to the pin on the bcm that corresponds to the brown or yellow wires.
Again not a guarantee test if no short to the case, but a smoking gun if it does.

 

[KingChuck24]

Ok so with only c4 in test continuity between the screw holes on the bcm and the wires coming out of the ignition. The actual case of the BCM is plastic and the only metal part is the screw holes.

 

[Gtstorey]

Disregard then, I was thinking the bcm had a metal case.

 

[KingChuck24]

Went to the salvage yard today and picked up a "new" bcm. Plugged it in and turned the key and got the anti-theft again. Tried to do a key reprogram but it did not work again. The one thing that did get fixed was the rear passenger brake light being always on because it was ungrounded. It now seems to be grounded and working again so I think at least something was wrong with the bcm. Now I am just not sure if the ECM or something else has gone bad. I have not yet checked all of the fuses on the bcm after putting it in but that is my next step.

 

[KingChuck24]

Went out and checked a couple more things:
First off the 2 amp ignition fuse is still blowing, I feel like this must be the core of the issue. How bad would it be to put in a higher amp fuse, I would assume something would get hot?
When the 2 amp fuse blows there is no power to the green ignition connector. When I replace it and do not turn the key it gets battery voltage but when I turn the key and the fuse blows no power.
I want to trace the exact path of the wire so that I can figure out if there is a short somewhere just not sure the exact path.

Edit:
So I found this diagram of the 2 amp fuse that is blowing

The only thing I could think of is the 1.3k ohm theft resistor is somehow bad making a short.

 

[Ross]

For debugging purposes, I have soldered a 12V light bulb across a blown fuse. If the fused circuit shorts out, then the light bulb will go full 12V bright. If there is no short, then the light bulb glows a little, and the circuit gets the rest of the power. This way you don't have to replace the fuse every time you test it.