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Discussion Starter #1
Hello everyone. I recently installed a 2008 Malibu engine into my 2008 cobalt.

Long story short the swap was very easy. However I've hit catastrophic snag. I ran the engine with then starter twice to get it lubricated before final start. Then I started the engine and it ran fine. I was using jumper cables all 3 times. I unplugged my cables and turned on the turn signal and the car died. I hooked up the cables again and now the car will not crank. I've verified the starter is functional and the new engine is not seized by jumping pins 30 and 87. I'm getting 12VDC constant at pin 30. I have no power at 86 or 85 with the key on and off. All grounds are grounded. The car acts like it's in gear and I can hear clicking on the passenger fuse panel. The fuse for ignition and ECM have power there. There are many in the engine bay box that do not. All plugs are plugged in. I unplugged 4 grounds. I have the alternator and the ground for the harness at the block together. The injector rail is grounded and the one on the transmission is grounded. The info system says power steering and the typical door ajar. If anyone can help me with more diagnostic procedure I would be eternally grateful as the ignition system seems to be spread out over several modules in this vehicle.

Again, thanks for any help you can provide.
 

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Also a BCM fuse in the trunk beside the battery.
 

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Discussion Starter #5
I checked that one as well and it is not blown. I am at wits end at this point. Any other ideas? The car acts like it's in gear but I know that isn't the issue because when I take it out of park and put it back in park, the doors lock and unlock.
 

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Maybe your crank position sensor.
 

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You mean it doesn't turn over at all?
 

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the engine will turn over using a relay bypass in the engine compartment fuse box. Pin 30 & 87
There is a nice replacement tool / switch to replace rhe run crank relay with a push button switch while testing in the engine compartment.
Need the schematic to show the relay & pins

Seems he has a bcm fritz due to voltage spike while jump starting.

Quick question
Did you connect jumper cables to the battery in the trunk?
Is this a 5 sp or Automatic Trans?
 

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Discussion Starter #10
To coby7; no sir. No crank, no click, nada! I have a YouTube video of my symptoms I will attach shortly.

Tbird; I was thinking that that is the most likely scenario. Someone also told me that it could be the switch though it giving out randomly like that just seems unlikely. I have confirmed that it will crank by jumping 30 and 87 ab d yes I do have one of those fake relay testers. I have the schematics. Yes I did connect them to the battery. It's an automatic.

YouTube video: https://youtu.be/rk0BYAzMTTw

Yes the car is very dirty, no it is not mine.
 

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Discussion Starter #11
From my understanding of the ignition system thus far, the switch itself sends a signal to the BCM which interprets the given signal as whether it being in off, acc, run or start. Whichever signal the BCM receives it sets the conditions for making that happen. I'd like to do a proper diagnosis so that I do not have to throw parts at it. I do have a test light, continuity tester, jumper relay, and a DVMM. So far I've gotten to the conclusion that either the BCM is NOT sending to signal to the ECM to energize or ground the relay or whatever happens. Id like to properly work my way from the switch, to the BCM, to the ECM, to the relay. I might add that the ECM fuse does have power under the hood, so do #8 and #25 in the passenger foot well. I don't think the BCM is totally dead as the radio still illuminates as do the lights on the instrument panel and a select few on the HVAC panel. All exterior lights work as well.

The car acts just as if you were trying to start it in gear, however I know it cannot be the PNP as the doors unlock when it's placed in park and the reverse lights illuminate when I have it in reverse. I have tried starting it in all gears.

The one tool I lack is a Tech-II scanner. I can likely rent or find a generic one however my ability go communicate to different system will be limited of course.

Thanks for any advice you can give me. I have the entire car put back together except for the fuse boxes. I've rechecked all my grounds. All of the plugs I removed. Everything.
 

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Transmission park possition sensor center console known to pop out of possition.
Then the BCM does not think tranny in park or neutral and will not send command to start

With wheels blocked, E- brake on....see it it will start in neutral

Thinking this will rule out neutral safety switch.
Will it not also check brake pedal switch to allow it to shift from park into gear?

What part of the world are you trying to breath life back into this Cobalt?
 

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Discussion Starter #13
I've tried starting in every gear so far. The doors lock and unlock when you put it in park so it knows agat gear its in. Also it shifts out of park with no problem.

I'm in Florida but I'd be willing to call or video call you if it helps.
 

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This is where I would love to be guided by Coby7 checking the systems with a Tech2.

Charlie, i believe your understanding ( logic ) is correct, as to the BCM operations.
One thing Coby7 repeats time and time again is loss of GM lan signals and fuze pitting yielding poor contact on the fuze terminals.
( uplug and reconnect the 2 gray connectors on the BCM)

You might call local garages or other forums for a local that has a Tech2. Dallas area is a bit far for me to pop over to explore.
The disconnect jumper cables and give a current draw by turning on turn signals is telling.....suggesting a voltage spike, fritzing the BCM.
Not saying the BCM is bad, but may need its configuration explored.
 

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I'm here now, My guess after all these convos is U may have a bad ignition switch. The start command is initiated by the BCM after receiving a start command from the ignition switch. If all parameters are met the BCM sends a start command to the underhood fuse block which in turn sends power to the starter. The most common failure I've seen on forum is a little trace that burns up under the fuse block preventing the power from going to the start relay. This has often occurred after multiple boosting. You can either repair the break with a jumper or replace the fuse block. I'm not saying 100% but what I've seen here. Personally it's never happened to me or my friends.
 

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Discussion Starter #16
You guys are freaking pros. So should I start diagnosis at the switch originally? Can you give me steps on how to do that? Also he is replacing his battery so we will no longer be boosting.

To tbird: ok, I'm slowly grasping what you're saying. I want to say I tried staring it again immediately after it died and I WAS getting the dead battery click but I can't confirm. I'll see if I can download Tech II and use my techstream (Toyota, Lexus and scion) VCM. So you think that the turn signal spiked the BCM and it's just acting wonky?

To coby: is there anyway to test the ignition switch itself? I cant find any literature on how to test the switch itself and what conditions that it needs to be performed under. Also can I just bypass that and just see if the BCM is sending out a signal to the fuse block? Switch>BCM>fuseblock. I couo d start in the middle by testing the BCM. If it's sending a signal know for a fact that it's receiving and I move to the fuseblock. If not, then I test the switch.

You guys have helped out tremendously so far. If you can get me over the goal line I'll have to buy you guys beer (or whatever beverage suits you!)
 

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My problem right now is all my photos were saved on photobucket and they screwed this forum over by not allowing third party use. Let me see what I can find and bring here for you. I don't know how savy you are with meters but you should get activity on pin 56 when turning the key to start. If you don't then ignition switch might be in question. If you do then check at underhood fuse block for start command.

 

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Discussion Starter #18
Ok. I have a continuity tester, a test light and a DVMM. I am very savvy with electrical meters. Yes, photo bucket has lost their minds with the third party hosting thing, I'm on another forum and it's very silly.

So is that BCM in that diagram the one that faces you when you remove the passenger fuse panel or is it in another location?
 

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That's it !
 

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Discussion Starter #20
Ok man!I should be back at the car tonight. I'll give you and update as soon as I get one.

And just to make it easier, do you know which pin is 56 in that photo?
 
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