08 Yukon Denali XL having electrical issues. Vehicle will not start.

[Doubeleive]

even new battery's can go bad, better to rule it out than chase a squirrel.
i put a new battery in the wifes surburban about a month later she went to the store was in there a couple minutes, came out truck wouldn't start, I went over gave her a jump and when we got back home I started testing stuff, battery read 12v's BUT it would not even roll a window up, soon as any kind of load was put on the battery it dropped to 5v, bad battery.

 

[Sevs]

I wouldn't use any water, if anything I would grab a can of crc battery cleaner at the autoparts store

When I reconnect the cables does it matter if negative or positive connects first and should I wait a minute in between when I reconnect?

 

[Doubeleive]

When I reconnect the cables does it matter if negative or positive connects first and should I wait a minute in between when I reconnect?

I usually put the ground on last, if you are just doing a quick disconnect to see if it clears a problem up then take both cables off and touch them together for a few seonds and then put them back on. I prefer to just take the ground off and then go turn the key a couple times, flip the headlight switch a couple times and press the brake pedal a couple times then go put the ground back on, but that's just me.

 

[Sevs]

I usually put the ground on last, if you are just doing a quick disconnect to see if it clears a problem up then take both cables off and touch them together for a few seonds and then put them back on. I prefer to just take the ground off and then go turn the key a couple times, flip the headlight switch a couple times and press the brake pedal a couple times then go put the ground back on, but that's just me.

I cleaned the connections reconnected the cables but same thing happened. An electric mechanic told me that this is a problem with the TCM or neutral safety switch. He’s been doing this for 30 plus years. Not sure what to thing just trying not to spend hundreds maybe thousands on the vehicle. I appreciate your feedback.

 

[Doubeleive]

I cleaned the connections reconnected the cables but same thing happened. An electric mechanic told me that this is a problem with the TCM or neutral safety switch. He’s been doing this for 30 plus years. Not sure what to thing just trying not to spend hundreds maybe thousands on the vehicle. I appreciate your feedback.

do you have a volt meter? dvom or whatever you want to call it
if so start checking voltages on the battery and battery cables, ohm check the ground cable from battery to where it mounts on the engine block
see what voltage you have at the fuse box, there is a cable that goes from the battery positive along the firewall to the fuse box, yours is 08 so you probably have the "mega fuse" on the firewall near the battery area, take that fuse off and clean that up also they get corroded just like battery cables.

 

[Doubeleive]

check this one, the 08 should have it, take it off clean all the contacts up real good and put it back on snug

 

[intheburbs]

Classic undervolt behavior. You have a bad battery, bad/loose cables, or bad/loose ground(s). I highly doubt it's a computer problem.

How new is the battery? Was it replaced about the same time these issues started?

 

[Sevs]

Issues started with the og battery which apparently was low. I have now replaced it with a interstate one.

 

[Doubeleive]

Issues started with the og battery which apparently was low. I have now replaced it with a interstate one.

you need a meter to test with, harbor frieght has them cheap, doesn't take anything special just a typical volt meter preferably one that can read ohm's also, your ground cables should read 0 ohm's for the most part you might get 0.2-0.4 depending on how firm the connection is.
if you have a lot of rust or moisture where you live you might want to pull the fuse box and check for corrosion underneath

 

[Mickey_7106]

When I reconnect the cables does it matter if negative or positive connects first and should I wait a minute in between when I reconnect?

Imo it's best to connect the positive wire last. When unplugging it's best to disconnect the positive side first.

Im my experience leaving the positive connected when disconnecting the negative wire it can still short out when in contact with metal surfaces. Does that make sense? Having trouble wording this am lol