2008 Cobalt LS 5spd No Crank - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

 
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post #1 of 7 (permalink) Old 03-02-2018, 10:29 AM Thread Starter
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2008 Cobalt LS 5spd No Crank

Ive read similar posts but have come up empty handed. My car ran fine last week and then when leaving work it seemed like the battery was dead. I got a jump from a friend and it worked. Later that night it did it again and this time i saw there was corrosion on my negative battery terminal. I took a brush and cleaned it real quick and she fired right up. I tested the multimeter on the battery and it was getting a charge from the alternator so i ruled that out. It died all of a sudden after driving it for three days in my driveway (luckily) this time it wouldn't even try to crank. I figured the battery was too far gone, so I replaced. Still nothing. Checked the crank relay and replaced it, nothing. It had a new ignition installed 3/4 years ago for the recall. I went to a junk yard and picked up a ecm since I lost communication with my computer via my scan tool. Ive checked everything. I can get it to turn over and start and drive by bypassing the relay. Its not great but it works. I need to find the problem though. Any one else who had this problem how did you fix it?
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post #2 of 7 (permalink) Old 03-02-2018, 07:21 PM
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Check your grounds. There is a thread here showing them. Check the BCM connector. Remove it an then reattach several times to clean the contacts. There are posts here explaining that. And also check the clutch safety switch.
Now you said you swapped out the ecm??? Shocked you got it to run at all. I didn’t think it would run until the security system enabled the new ecm. That is a 30min task.
Me thinks not all the info shared


So jpgerner, tell us more about your Cobalt, factory options, add one such as remote door entry, mileage.
Did you get the ground locations diagrams from the thread Ground Location Images and check them/ remove, clean, reassemble & coat with a protective coating? What do you mean by had a “new ignition installed”.
When you turn the car to on, do all of the lamps in the instrument panel illuminate? What lamps stay on.

Lost com with computer....this is very telling..... what city does & has this car live/lived

Until you give a little more, all of this seems to be pointing to dirty connections to your bcm

BC

Last edited by 1966tbird; 03-02-2018 at 08:58 PM.
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post #3 of 7 (permalink) Old 03-03-2018, 09:22 AM Thread Starter
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Thank you tbird, I will try the grounds next.

Some more information. Originally from ohio, the car is with me in nashville. Its a plain jane model, so nothing fancy. I did do the security check with the replacement ecm, but now I'm thinking it might have been a ground the whole time and not the ecm at all. It was just weird because it died and then wouldn't crank, and then wouldn't even take a jump. I thought of the clutch switch as well but haven't tested it yet, its a pain to get to. Also seems weird to me because it worked fine until a week ago. Currently, everything lights up, only thing that stays on is the check engine. It says power steering but it works, and change oil. the speedometer doesn't work though.

Also i meant that the ignition was replaced with the recall a few years back
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post #4 of 7 (permalink) Old 03-03-2018, 01:21 PM Thread Starter
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Okay, so I tested all the grounds for under the hood and in the trunk and they were good. I found the one by the e-brake but couldn't find or get to the one under the seat. The clutch safety was a pain and couldn't really get to it either (have any suggestion on how to make that one easier for me to test?) anyway I unplugged them all, cleaned them and put them back together. The bcm fuse in the trunk checked out and so did the wires, however the ones under the hood although they were fine, the 30 one wasn't getting a ground, only a positive pin. the other was getting both but my test light flickered a bit while testing it.
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post #5 of 7 (permalink) Old 03-03-2018, 11:04 PM
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Seems like you might have a poor connection at the BCM itself. @Coby7 has posted the schematic and pi outs for these connectors. With that you could verify the switch operation. A great wealth of information.

BC
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post #6 of 7 (permalink) Old 03-05-2018, 12:37 PM Thread Starter
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Hey @1966tbird , thanks for all the help on this goose chase. Okay so I found another forum where you and coby posted the schematic for the bcm. I know that pins 56/62 are super important one for the switch and one for the crank. on bcm2 pin 62 does not have any power at all! 56 only when key is on acc or on position. Could that be something thats wrong? argh I just want to figure this out so Im not so stressed. again thank you for all your help

Last edited by jpgerner; 03-05-2018 at 06:12 PM.
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post #7 of 7 (permalink) Old 03-05-2018, 11:26 PM
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My photographic memory is a wee bit low on film today and some of my film stock is a bit foggy.
Post the links to those schematics so others can follow.
As to chasing the goose. Way too many times without the schematic thatís what folks are left with. Very frustrating.

So
That leaves us to start at where we know problems start with the poor connections.
Those connections at the BCM are known to become corroded. Again this is not a 57 Chevy where everything was 12V or ground. So a simple probe light is no longer enough. With that said we are working on a computer controlled POS so all of those flakey grounds must be good or we start to run into the problems you describe.
So many of these connections are simple logic levels or GM LAN, network signals.
JPgerner.
Disconnect your BCM connector another couple of times and remove the fuses clean the terminals and reinstall. The fuse terminals get pitted, build up a carbon track, then open the circuit. Even with a good fuse, if both sides do not make, contact......no complete circuit.

Now once you know a connection is good, repack, it with dielectric grease to extend its life it time between the next problem.

Pull up the schematics, I donít have them with me right now, and verify you are getting 12V power to the BCM.
Verify your fuses!!

Oh, on pin 62 on the BCM C2 is the 5V reference signal to the ingnition switch and 56 is the signal return to the BCM
This +5V on pin 62 with respect to Chassis Ground.
Then you will get different +voltage levels (0V-3V) on pin 56 depending on the ignition switch position, with respect to chassis ground.
Most of the schematics can be found in this thread
https://www.yourcobalt.com/forums/pro...-no-crank.html
Now from Autozone here is their starter electrical wiring diagram

Enjoy
And let us know your progress

BC

Last edited by 1966tbird; 03-05-2018 at 11:47 PM.
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