I don't see that U code in any of my stuff, but U is communication error codes. they aren't always linked to an specific module just that that module said it's not getting the data is looking for.

I'm personally horrible with can stuff. you might need to get a monthly subscription to like all data or something with diagnostic trees. maybe a gm service manual at this point for that one.


edit.. something I did see that sounds silly but if you bought it from someone not running. if the engine is locked up the notes say the motor in the tranny can't spin it. worth putting a wrench on it and make sure you can spin the engine over.

 

I did find it, just didn't come up in a search

 

Absolutely.

All blocks must be over 12V or some other value before the relay will engage.

Is that reported by the tool or as measured by a voltmeter?

Block 1 is typically the pair of modules where the main (-) cable attaches.

By that logic, block 11 will be modules 21 and 22 counted from the (-) end (just past the middle of the pack).

 

That is read from the tool, I'll have to verify on the battery.

 

If the tool read it, then that's what the BCM is reporting, and it's absolutely, positively A reason it won't start.

You may have a broken terminal, sense lead, sense wire or corroded pins in the BCM.

It's conceivable, but not probable severe corrosion could be at play.

If you have to loosen any terminal nuts, they really need to be properly torqued when reinstalled, 48 in-lb. If you don't have a suitable torque wrench, get one.

 

I took a look at the individual terminals on my battery pack and there is some corrosion starting on several contacts.


I found a "best hybrid battery" out of a Tahoe part out on marketplace for 400 bucks, it's been sitting a year since the gas engine went out, would you take a chance on it?
https://www.besthybridbatteries.com/...hevrolet/tahoe

 

If you're okay with a total loss on it, sure. I would NOT install it without confirming all module voltages are above 7.4V.

Even so, put it on the charger for about 2 hours.

 

I got him down to 200 and would accept that total loss

 

like

Worst case, you have a harness that likely works, and it improves your chances of being able to get a good battery out of two.

Again, do not just "try" it and see if it works. Sitting for a year is almost a guarantee you have multiple modules out of range, and that may kill them if they're not out of range.

Charge for at least two hours, four even better.

 

​​​​​​Ok