Interesting Diag

[clinebarger]

This was a referral buy a long time client, 1994 C1500 with a "K" code TBI 5.7L/4L60E with 93,000 miles. Nice truck other than the sun beaten dash.
Complaint....Battery is completely flat after 5-6 days.

Knowing old retired folk like I do, I asked him about his driving habits. He goes to the Pharmacy then to the Grocery store once a week which is a one mile round trip with 3 engine starts. I advised that even if I do find a draw....The battery is going to get depleted anyway unless he take longer drives.

This truck has been to a couple local shops, One being a guy I've known for years & is pretty good with electrical.

Hooked up my Multimeter in series set on the 2 amp DC scale & had a 38mA draw, That's not much more than I'd like to see on a modern vehicle, But far more than this old truck should draw.

Whipped out the Thermal Imager just for experiment sake, Nothing. Pulled fuses one at a time...Nothing other than a the 5mA that the PCM drew.

Decided to separate the Body from the Underhood electrical buy unhooking the Bus Bar form the Battery.....Draw went to Zero. Meaning the draw was inside the cab NOT under the hood.

Unhooked the eyelets one at a time at the Bus Bar 'til the draw went to 5mA.
Left the offending circuit unhooked, Started the engine & proceeded to check what wasn't working. The Radio & HVAC Control Head were dead.
The HVAC Control Head was the easiest to unplug & ended up being the parasitic draw.

Had a used HVAC head stashed back.....With everything hooked up....

PCM, 5mA
Radio, 2mA
HVAC, 2mA
For a total of 9mA of parasitic draw.



Closing....The HVAC control head was drawing 29 milliamps more than it should've, Don't shrug off customer complaints!!

 

[demarpaint]

Great diagnostic work. Around here they would have probably rewired the entire truck five times only to have it burn to the ground.

 

[ls1mike]

That is some good troubleshooting. I have been involved in similar types, but it is usually on Submarines. Knock on wood I have never had a car hate me so much that it has done that to me. However I have had a Submarine dislike me.

 

[flanso]

@clinebarger, please explain disconnecting the bus bar and why disconnecting it separates the body from the underhood electrical. Is a bus bar part of the fuse box? I always enjoy and learn from your postings. Thanks.

 

[wpod]

Awesome 1

That is some good troubleshooting. I have been involved in similar types, but it is usually on Submarines. Knock on wood I have never had a car hate me so much that it has done that to me. However I have had a Submarine dislike me.

Subs are supposed to dislike you. That is all I know about Subs.

 

[AZjeff]

That is some good troubleshooting. I have been involved in similar types, but it is usually on Submarines. Knock on wood I have never had a car hate me so much that it has done that to me. However I have had a Submarine dislike me.

How big is the bus bar on a submarine?

@clinebarger, do you do this sort of work all day or do you get easy stuff as well? Always interesting reading how a pro works.

 

[ls1mike]

Awesome 1

Subs are supposed to dislike you. That is all I know about Subs.

You are not wrong...hahahahahah I see what you did there.

How big is the bus bar on a submarine?

@clinebarger, do you do this sort of work all day or do you get easy stuff as well? Always interesting reading how a pro works.

I could tell you...but... hahahahhaah

 

[andyd]

First rule in trouble shooting is to divide the ckt to isolate the trouble.Great job Cline Barger

 

[zrxkawboy]

First rule in trouble shooting is to divide the ckt to isolate the trouble.Great job Cline Barger

+1. When I was in tech school (electronics) our senior instructor drilled into our heads, “Divide and conquer!”.

 

[montenope]

That is some good troubleshooting. I have been involved in similar types, but it is usually on Submarines. Knock on wood I have never had a car hate me so much that it has done that to me. However I have had a Submarine dislike me.

Is that a Trident sub in your avatar pic? Ohio class?

 

[ls1mike]

Is that a Trident sub in your avatar pic? Ohio class?

Yes it is.

 

[montenope]

Cool.
I was a paint technician on them many years ago.
Best job I ever had and gives me great pride to this day to
know that I was a part of it.
Love that picture.

 

[GMBoy]

That is a timely post because I have a 91 K1500 coming to my shop with the same complaints....I will follow your lead!

 

[ls1mike]

Cool.
I was a paint technician on them many years ago.
Best job I ever had and gives me great pride to this day to
know that I was a part of it.
Love that picture.

I did 12 patrols on 2 different ones. Michigan and Alaska.
That picture has made the rounds. It is all over the net now.

 

[montenope]

Yep I worked on both of those.
And to think I've stood exactly where you took that picture from. Lol
Small world.
Worked on 726-732 and fast attacks 701-702.
EB in Groton is where I worked back in the early 80s.

 

[andyd]

Yep I worked on both of those.
And to think I've stood exactly where you took that picture from. Lol
Small world.
Worked on 726-732 and fast attacks 701-702.
EB in Groton is where I worked back in the early 80s.

About that time, I spent a winter at GD Fore River setting 2" 5'x5' lead sheets in a frame for a sub's reactor shielding. Wasn't a bad job

 

[clinebarger]

@clinebarger, please explain disconnecting the bus bar and why disconnecting it separates the body from the underhood electrical. Is a bus bar part of the fuse box? I always enjoy and learn from your postings. Thanks.

This is some ancient stuff now days, But all the main power feeds come from the under hood Bus Bar via Fusible Links. Simply disconnecting the leads one at a time can narrow down the draw to a few components.

These old GM trucks have a tiny fuse box under the dash.

Bus Bar....