Lost 3rd and 4th outta no were?

Tiny
JUNIORANDTAYLOR
  • MEMBER
  • 2007 CHEVROLET SUBURBAN
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 330,000 MILES
I am getting a code on my scanner saying ign 1 circuit low/open on bcm pin 1 and 5. Reason for checking it was I lost 3rd and 4th gear outta know were. I know the trans is still good because when I pull the fuse for the trans I got 3rd and 2nd
Tuesday, December 2nd, 2025 AT 4:09 PM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,610 POSTS
Hello,

I can help you with the problem, please tell me which number code you are getting. It sounds like you have a shift solenoid that is out which can cause this issue. The transmission takes 3 fuses to run here is a guide to help you test the fuses and to make sure they are getting power.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the images (below). Let us know how it goes
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Wednesday, December 3rd, 2025 AT 10:18 AM
Tiny
JUNIORANDTAYLOR
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  • 3 POSTS
Im getting codes 1370-06 and a u0100 or something like that. Which says ignition short to ground. What I really need is a wiring diagram and pin out. Its a 07 suburban. 5.3 and 2wd
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Thursday, December 4th, 2025 AT 8:02 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,610 POSTS
The short to ground can be the shift solenoid shorted out which is common. I would use a volts meter and check the shift solenoids to see which one is shorted. This guide can help.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

B1370-06 (most likely what you’re seeing) “Device Ignition 1 circuit - short to ground or open”. It’s usually set by the SDM (airbag module) or BCM, not the engine ECM.

U0100 - Lost communication with ECM/PCM (CAN bus). That’s often a symptom of the IGN 1 power dropping out to the ECM rather than a network failure.

Also, here is the wiring diagrams for the ignition switch so you can check the feed wires, also, check all of the fuses with the key on as well. Check out the images (below). Let us know what you find.

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Friday, December 5th, 2025 AT 10:57 AM
Tiny
JUNIORANDTAYLOR
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  • 3 POSTS
I will check it out and let ya know I greatly appreciate the advice on how to trouble shooting it I bein pulling my hair out with it lol.
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Friday, December 5th, 2025 AT 5:33 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,610 POSTS
Yep, a step at at time will get us to the fix we need to get you back on the road.
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Saturday, December 6th, 2025 AT 8:56 AM

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