Service Brake System message

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
I went back outside one more time to check something. I unplugged the negative from the good battery and plugged the negative into the "bad" one. Key on and I have my condition. "Service Brake System", @Chevy1925 I even checked the codes for you and nothing. I have three, one for headlamp circuit (not sure why) and 2 for my seat heaters.

Started the truck on this battery with no issues except for the voltage was all over the place, dropped down to 2V then to 7V to 9, back down 6 then all the way up to 11.8 or something along those lines.

What is this truck telling me? Bad ground on the passenger side battery causing electrical funkiness? The fact that I got my condition from the passenger side battery being plugged in and not the driver side can't be coincidence.
 

2004LB7

Well-known member
Dec 15, 2010
6,202
1,634
113
Norcal
I went back outside one more time to check something. I unplugged the negative from the good battery and plugged the negative into the "bad" one. Key on and I have my condition. "Service Brake System", @Chevy1925 I even checked the codes for you and nothing. I have three, one for headlamp circuit (not sure why) and 2 for my seat heaters.

Started the truck on this battery with no issues except for the voltage was all over the place, dropped down to 2V then to 7V to 9, back down 6 then all the way up to 11.8 or something along those lines.

What is this truck telling me? Bad ground on the passenger side battery causing electrical funkiness? The fact that I got my condition from the passenger side battery being plugged in and not the driver side can't be coincidence.
Bad ground or positive can do it. Have you tried swapping the two batteries. Put the suspected bad one in the driver side and see if it behaves the same? That should tell you if it's wiring or battery
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
No but I can certainly try that. I will do that and report back.
I do have 2 other 750/800 CCA batteries I can always toss in and try as well. One is brand new off the shelf but the other is older.


@TheBac You would be the first to publicly declare alternator I think.
 

TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
15,215
1,494
113
Mid Michigan
a few years ago, when my truck was killing the batteries quickly for no apparent reason, I had the alt tested and found it had an internal short. Would still charge, but would drain the batteries down to nothing when the truck was shut down. I went over everything and anything electrical before I had that alt tested, too.

Basically, dont trust that everything electrical is working as it should.
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
Swapped the batteries and condition does not show its face. WTF. Did a key on with each side disconnected one at a time and never saw the SBS message. Lights dimmed pretty hard I thought it might happen but no. Wonder if maybe that means it is grounding issue and the "good" battery had enough juice for that not to occur.

@TheBac I don't trust anything electrical period. I have no problem pulling the alt and taking it to get tested at this point.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,008
4,582
113
Phoenix Az
What are you using to monitor voltage during cranking?

Also, you really should be load testing these outside the truck. Takes all the truck variables away
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
All I’m using is the voltmeter and my eyeballs. I guess technically not my eyeballs they were my dad’s. :)

I can pickup that carbon pile tester tomorrow after work. I refuse to go the NAPA near me.
 

Ron Nielson

Active member
Oct 11, 2009
660
109
43
Berryton, KS
Follow the negative cable down to the side of the block near the front of the engine, remove the bolt, and use a wire brush on the block and cable end until shiny. Replace the cable and bolt and tighten. Very easy to do. I can't say it will help, but you will know for sure that the ground is as good as you can make it.
 
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2004LB7

Well-known member
Dec 15, 2010
6,202
1,634
113
Norcal
Most voltage meters dont have the response time needed to see accurately what's happening during cranking. Too much noise on the cables and voltage fluctuations for a typical DOM.

That's why those resistor style load testers work so well
 
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1FastBrick

Well-known member
Dec 1, 2016
2,119
761
113
Junkyard
Yes the climate will affect it a very small amount. Not huge swings though.

Do you have the digital climate control or manual levers?
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
@Ron Nielson You are talking about the negative cable on the passenger side, correct?

Order is placed for the load tester. I will pick it up today, drive the diesel to work tomorrow so that when I come home the batteries should be all charged up and ready for me. I'll pull the batteries and then test them on Wednesday.
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
Just to note it froze over night at some point. "Good" battery on passenger side, "bad" battery on driver. No SBS message or flickering lights this morning (I have some LEDs overhead and they flicker all the time, so some flickering is normal. I need to fix that.)

Just a note, that is all. Tonight I will pull the batteries and then test them with the tester tomorrow.
 

shakenfake

Moron
Sep 15, 2022
175
53
28
Shlumpt, TX
It is not all the time. I would say more times than not though and not while running. I don't have any 194 halogens I could test right now either. When I got the truck, I had thought both of them were burnt out but later discovered that when someone redid the headliner, they plugged in the onstar to the map lights.
The exterior lights do not flicker. Only the LEDs I put in the license plate housings. Which actually were burnt out.

@2004LB7 It is funny, if you look up "Bad diode in alternator causing..." the first auto fill is "battery drain" :ROFLMAO: