2001 yukon electrical issue

[billystrong]

Hello everyone, I bought a 2001 yukon slt. It has a issue in the mornings. I have to jump it every morning, it runs all day. Start stop off on all day. The battery is good and the alternator is charging, but in the morning it just won't fire up with assistance. Anyone have this problem. I believe it's a ground problem, but which one? Thanks

 

[Fless]

Do a parasitic draw test to see if something is staying awake.

 

[lyncht1967]

as a test connect one end of a black jumper cable to batt negative and other end of black jumper cable to block somewhere and try cranking...if it starts you have a bad negative battery cable..common on these models. can do the same thing from batt pos to starter pos and try cranking..if it starts you have a bad positive battery cable. common issues on these models...i had the same issue a month ago and it was bad negative batt cable.

 

[Matthew Jeschke]

You can also do a current draw test. Don't start anything, with car off (and doors closed for a while (BCM may wake up if you fiddle with doors). Hook a DMM / volt meter in series w/ either battery cable... That is disconnect one of the battery and complete the circuit with the dmm. Read your amp draw. You should have a very minimal reading. I don't know the exact spec...

If it's drawing current which honestly, it is from what you're saying. Might be a moot point to even do that test...

Get a test light. I have a power probe (brand name) and LOVE it. Test all your circuits in the junction / fuse boxes) to see which one / ones are drawing power w/ the car off.

You can also test your grounds... sometimes it's as simple as a poor connection to battery as @lyncht1967 is talking about.

 

[Fless]

You can also do a current draw test. Don't start anything, with car off (and doors closed for a while (BCM may wake up if you fiddle with doors). Hook a DMM / volt meter in series w/ either battery cable... That is disconnect one of the battery and complete the circuit with the dmm. Read your amp draw. You should have a very minimal reading. I don't know the exact spec...

If it's drawing current which honestly, it is from what you're saying. Might be a moot point to even do that test...

With everything asleep on this body style, anything under 50mA (0.050 A) is acceptable. Even better that many of them easily go below 25mA; mine rests at 16mA.

Note that if you have the AUTO HVAC control unit, those can take up to 4 hours or so to fully sleep. They draw probably 60-100mA before going night-night.

 

[Marky Dissod]

For the current draw test, the second step (takes awhile) is to remove each fuse.
With luck, when you pull one of the fuses, the current draw will drop significantly.
The fuse that you just pulled is a problem, if not THE problem.

 

[Fless]

For the current draw test, the second step (takes awhile) is to remove each fuse.
With luck, when you pull one of the fuses, the current draw will drop significantly.
The fuse that you just pulled is a problem, if not THE problem.

Pulling fuses can be counterproductive or confusing, since one circuit can affect several modules. Easier method is to measure the test points for voltage across each fuse to see if current is flowing. Power Probe has conversion charts online to calculate how much current is flowing based on the mA measured.

EDIT: Some good tips here, along with a link to the Power Probe chart.

Advanced battery drain diagnostics

Let’s review some time-honored methods as well as explore new methods for unmasking phantom battery drains.

www.vehicleservicepros.com

 

[slypher25aussie]

Aaaaaand crickets lol.

But in the off-chance the OP comes back to read and reply... you said your battery is good. How do you know? Was it tested professionally to be good? You said you start and stop the truck all day. That would wreak havoc on a battery. Is it cold in the morning where you live? All these things can affect a battery's performance.