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Code U0140, started and ran for a few seconds, now will not start, replaced battery?

Tiny
DJREES
  • MEMBER
  • 2007 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
Troubleshooting the truck listed above 5.7L, 4 door Extended cab, that will not crank. Have a U0140 Code, no communication with BCM.
Have no door locks from door switch or key fobs, no dome lights, power windows inoperable. Replaced the LTR 20-amp fuse (55) in the under-hood fuse box. Removed an aftermarket alarm that was connected to some of the BCM wiring. Still no crank even with that removed.
I would like to have a pinout of the BCM wiring and the expected voltages so I can check it further.
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Saturday, August 20th, 2022 AT 5:32 PM

10 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

I attached the wiring schematic which includes the pinouts below. The schematics were three pages long, but I had to cut each one in half to make them readable. I did overlap them so you can follow from to the next.

In most cases, the output voltage is indicated at the BCM. If there is something specific you are looking for, let me know and I should be able to find it for you.

Take care and let me know how things work out for you.

Joe

See pics below.
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Saturday, August 20th, 2022 AT 10:04 PM
Tiny
DJREES
  • MEMBER
  • 6 POSTS
Joe. Thank you for the schematics. I just want to check all I can voltage wise to verify where the problem might be. Just helping out a friend. I don't want to replace the BCM unless I have ruled out the other possible causes. I used to be a Chevrolet technician years ago.
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Sunday, August 21st, 2022 AT 6:34 AM
Tiny
DJREES
  • MEMBER
  • 6 POSTS
Joe, can you provide the recommended troubleshooting steps for the U0140 DTC? Right now, I have access to a GM TECH2 scanner. I would love to have a troubleshooting guide to follow to make sure I am not overlooking anything.
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Sunday, August 21st, 2022 AT 7:29 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

I would be happy to, but it doesn't appear to be relevant for this vehicle. I attached the U codes from my manual. Could you have possibly missed something?

Let me know.

Joe
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Sunday, August 21st, 2022 AT 5:17 PM
Tiny
DJREES
  • MEMBER
  • 6 POSTS
Joe, see attached image from Tech 2.
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Sunday, August 21st, 2022 AT 8:21 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
I found it in a different manual. I have no idea why it isn't listed in the one I normally use.

If you look below, I attached the description and diagnostics. I also attached the data communications schematics.

Take a look through them and let me know if they help.

Take care,

Joe

See pics below.
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Monday, August 22nd, 2022 AT 8:21 PM
Tiny
DJREES
  • MEMBER
  • 6 POSTS
Joe, thank you very much for the information. I need to do the test on the Serial data communication enable circuit and the accessory wakeup serial data circuit. I believe the Serial Data communication enable is the TAN/BLK that is labeled HI SPD GMLAN SERIAL DATA BUS (+). Would you agree? Do not want to put a test light to the wrong circuit and cause more damage.
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Tuesday, August 23rd, 2022 AT 7:08 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

You are very welcome. Also, looking at the schematics, you appear to be correct. Also, if you are using a test light, it shouldn't hurt anything.

Take care and let me know how things turn out for you.

Joe
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Tuesday, August 23rd, 2022 AT 7:15 PM
Tiny
DJREES
  • MEMBER
  • 6 POSTS
Joe,

After testing everything, we decided it needed a BCM. Ordered refurbished BCM. Vehicle now starts, but has several new problems, including battery discharged overnight. Exchanged for another BCM and all is okay now. Thanks again for all your help.
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Thursday, October 27th, 2022 AT 4:17 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,758 POSTS
Hi,

Thanks for the update. I'm glad to know it has been repaired and is running properly again.

Please feel free to come back at any time in the future. You are always welcome here.

Take care,

Joe
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Thursday, October 27th, 2022 AT 6:02 PM

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