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

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KingChuck24

Well-Known Member
So today was another test drive and this time we went a little further than normal. The roads we were on were a little bumpy and it ended up knocking off the ground wire from the battery while driving. We reattached it and when we did the car went into anti-theft mode. We tried reprogramming the key about 3 times but we couldn't get it to work. We then tried to original key to the car and that one would work either.
After further inspection and going through the BCM fuses we discovered that fuse number 1 and number 22 were blown which is the 10 amp and the 2 amp. We replaced both and connected the battery and after turning the key to the run position they both blew again.
The car has an aftermarket supercharger so the heat exchanger pump is wired in through the ECM fuse on the fuse box. We unplugged that and changed both fuses and now only the 2 amp ignition fuse is blowing.

Before all this, it is worth noting that the car, before starting, would turn on fine but then when turned to the start position all the electronics would shut down and the only way to solve this was to disconnect and reconnect the battery.

Not very good with the electrical side of this but my first guess would be something to do with the ground. I went through and they are all still connected so I am not entirely sure.

Any help would be much appreciated!
 
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KingChuck24

Well-Known Member
A little update:
Came back this morning to keep trying some things, first I replaced the ignition fuse and turned the car on. Anti-theft engaged but this time the ignition fuse did not blow and all of the other fuses were good. I tried key reprogramming again but it did not work. I then decided to go to home depot to get a new key because that is what worked for me last time when starting the car. I went through the key programming procedure and it looked promising as the anti-theft light turned off after all three ten-minute marks but after the third one was finished I turned it off and back on again and the anti-theft light was still on. I also noticed that the rear passenger brake light remains on while all of the other lights are off, not sure if this is related to the anti-theft or not.
 
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KingChuck24

Well-Known Member
So today we tried getting a new key from the Chevy dealer and that one also did not work. I called up a friend who has an HP tuners device and he came over. When we connected the device to the car (which is still in anti-theft mode) the device turned green, but when trying to read the vehicle it kept spitting out "un-supported interface". Not sure if we were doing something wrong. The HP Tuners device is also an mpvi2 with RTD+ and it was bought off a website to tune a mustang so I am not sure if that matters.
 
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KingChuck24

Well-Known Member
Yes that seems likely now but last time the anti-theft shut off with a different key so we just had to be sure.
 
K

KingChuck24

Well-Known Member
Did some testing today and I was not able to find anything out of the ordinary with any of the connections. The scanner that I have cannot connect to the car right now and I think it is because it is in the anti-theft mode. I was wondering if I needed a tech 2 scanner to be able to scan the car if it is in anti-theft mode. Would the HPT mpvi13 be able to connect to the car if it is in anti-theft mode?
 
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KingChuck24

Well-Known Member
If it is a data wire issue how might I go about testing.

40277

I know the data wire coming out of the alarm module is number 4

40278

And then it seems to go to pin 38 on the bcm,

That is the extent of my knowledge currently but I will keep looking around for more info and do some more testing.
 
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KingChuck24

Well-Known Member
I did the tests on the OBDii and here is what I found:
4-16 12v
5-16 12v
6-14 61 ohms (I think this is ok because it is +-1 ohm)
1-ground when key is turned on shows .3 on my ACV reading
6-14 when key is on shows 1.8 to 1.9 on my ACV reading

From my understanding pin 1 which is low-speed GMLAN is the one that connects to the anti-theft and its reading close to zero so that seems to be an issue.

Edit: Have been researching a little and figured out that the low-speed GMLAN should be 5V
 
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Gtstorey

Goblin Guru
Pin 1 voltage at 0.3v might be a problem, although trying to check with a volt meter can be difficult. The voltage you are reading is an average, and the circuit voltage will depend on the activity of the modules, which there aren't a lot of on a Goblin.

Check your supply voltages and ground on the TDM.
 
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KingChuck24

Well-Known Member
Went through the voltages and the grounds of the TDM. Pin 1 got 12 Volts, pin 2 which is accessory power had no volts, pin 3 no volts which would make sense because it is ground to ground. Pin 4 which is low speed GMLAN was fluctuating between 0 and .3 volts.

I am measuring these with the connector unplugged as there is not a way to get to the cables with it plugged in.
 
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Gtstorey

Goblin Guru
Did you confirm continuity to ground on pin 3, not voltage? Although if it wasn't grounded, you would have seen voltage there.

Hard to tell from the diagram above if you are supposed to get voltage at pin 2, but I think so. Need to check the power distribution schematics to confirm.
 
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KingChuck24

Well-Known Member
Yes there is continuity to ground from pin 3. The only one that does not get ground is pin 4.

Edit: I think the schematic above shows that pin 2 should get voltage.
 
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KingChuck24

Well-Known Member
Ok went through and checked the voltage on the BCM and it looks like C8 on BCM C4 (c4 is which multi plug not a pin) is getting no voltage, on top of that I went through every other BCM connection and on BCM C4 pin D1 had no voltage. D1 is listed as a battery-positive voltage. On BCM C3 pin B5 which is listed as acessory voltage is also not getting any power.
 
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