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post #1 of 9 (permalink) Old 09-24-2017, 01:35 PM Thread Starter
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No Crank/no Start

Weird electrical problem:
With ignition in crank position there is 12 volts going to starter signal wire as long as it is unplugged from starter but shows 0 volts if plugged into starter?

This is actually on a 2008 Pontiac G5 but should be same setup as cobalt here
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post #2 of 9 (permalink) Old 09-25-2017, 12:03 PM Thread Starter
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Quote:
Originally Posted by kitbuf View Post
Weird electrical problem:
With ignition in crank position there is 12 volts going to starter signal wire as long as it is unplugged from starter but shows 0 volts if plugged into starter?

This is actually on a 2008 Pontiac G5 but should be same setup as cobalt here

Also not hearing the fuel pump coming on either. This vehicle has been to the local dealer for this issue in which they performed an ignition recall I believe (replaced ignition?) and still could not figure out what was going on. Not sure how much troubleshooting they performed after replacing the ignition switch as the previous owner may have had the vehicle picked up before they completely diagnosed it due to the bill that is was racking up. Anyway....now it is my problem to figure out!

---------- Post added at 11:03 AM ---------- Previous post was at 10:57 AM ----------

One other thing I forgot to mention.....engine light is on with code P1682 which I have been previously told should not cause a no crank condition but can cause a no start or reduced power condition. Another weird thing about this code is that I really can't clear it. When I command to clear codes and then immediately perform another scan...the code is still there. This is even the case without trying to start the vehicle in between clearing the codes and performing another scan. Not sure if this is related at all with my problem of no crank but just some more info.
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post #3 of 9 (permalink) Old 09-25-2017, 12:39 PM
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Did you check the big fuse in the trunk? Did you check your battery voltage with the light on? Did you check all the fuses in the underhood fuse block? If the fuel pump isn't coming on you are not getting the crank signal from the BCM...

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post #4 of 9 (permalink) Old 09-25-2017, 01:32 PM Thread Starter
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Did you check the big fuse in the trunk? Did you check your battery voltage with the light on? Did you check all the fuses in the underhood fuse block? If the fuel pump isn't coming on you are not getting the crank signal from the BCM...
Big fuse in trunk is good. Battery voltage may be low now but was good while checking, I will recharge and check to make sure it is up to par before proceeding with further tests (or install another battery). All fuses underhood fuse block are good.

Sounds like I need to look into why I am not getting crank signal from the BCM, suggestions where to start there? Weird why I get 12 volts from signal wire to starter when unplugged from starter but 0 when plugged into starter. Also when I check voltage at the crank relay plug (with relay unplugged), in order standing from front of car this is what I get.....
Key on top left = @2-3 volts(?), top right = 12V, bottom left = nothing (I believe that is the signal wire to the starter), bottom right = ground
Key start top left = @9-10volts(?), top right = 12V, bottom left = nothing (if this is signal going to starter then relay would have to be plugged in to get something here), bottom right = ground

I also checked all of the above with the relay installed but left up just enough I could get the pins of meter on the relay pins and got the same as above with the exception of the bottom left in the start position....I would get the 12V on the bottom left in the start position as long as the signal wire was unplugged from the starter. As soon as I would plug the wire back in to starter I would get 0 volts on this pin.

That baffles me....why would just plugging that wire in to the starter cause it to show 0V but when unplugged it shows 12V?


Thanks for your help with this matter Coby7!

Last edited by kitbuf; 09-25-2017 at 01:34 PM.
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post #5 of 9 (permalink) Old 09-25-2017, 05:55 PM
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The reason you get 12Volts is because there's a pull-up sense resistor on the BCM module. Normal I believe.

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post #6 of 9 (permalink) Old 09-25-2017, 06:41 PM Thread Starter
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Originally Posted by Coby7 View Post
The reason you get 12Volts is because there's a pull-up sense resistor on the BCM module. Normal I believe.
Ok, can you tell me how to check for why I wouldn't be getting a crank signal from the BCM like you were referring to in your earlier post. Thanks.
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post #7 of 9 (permalink) Old 09-26-2017, 03:16 PM Thread Starter
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Question

Coby7
Can you explain how I need to troubleshoot why the BCM would not be sending a crank signal to the crank relay?
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post #8 of 9 (permalink) Old 09-26-2017, 05:09 PM
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I really don't know what to tell you, maybe trace why your fuel pump isn't coming on, maybe they are related.

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post #9 of 9 (permalink) Old 09-26-2017, 05:48 PM Thread Starter
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Do you think it could be a issue between the ignition switch or BCM.

---------- Post added at 04:48 PM ---------- Previous post was at 04:39 PM ----------

Tbird,
Any advice you can offer.
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