Service Brake System message

[shakenfake]

Need some help from people more smarter than I,

Last year around this time I replaced my batteries after getting a "Service Brake System" message on my DIC. There were a couple of other things that I noticed as well but after the battery replacement the message never came back, and all was well through the rest of the winter. This issue was also happening when it was 80* out last time but I haven't hit 80* this late in the year so I couldn't be sure if this is something cold weather related or not. Today was 29* and it popped, the other day was ~55* and it popped as well.
However, I am once again receiving this message. I'll get that same "Service Brake System" message on the DIC, along with what seems to be a real low reading of voltage on my battery coming from the gauge, I also will get kind of a longer start but that could just be winter diesel stuff (I think I am imagining it).

The message only pops on when I turn the key to key on engine off and then goes away after maybe two seconds. Never see it again until I try to start the truck again, but it is not every time I start the truck. No lights are on the dash although I have not scanned for codes when that message does pop. The last time I scanned for codes was sometime in the summer and I did not have any. I plan on taking my batteries to get tested at O'Reilly over the weekend to see if maybe it has something to do with the batteries being dead or low. If they are dead or low, I do not believe that it is inherently related to my last battery purchase. These batteries replaced mismatched different aged batteries, 2 years and 3 years old which in the past 10 years I would say is about on par for me.
With electrical load and the engine on the gauge does jump up to 14 volts. It does not stay there though and does a lot of moving around, as far as I am aware this is normal with the later year GMT-800s. It starts out with key on engine off at 10ish.

Relating to brakes...
I did check my brake fluid and it looks clear and topped up. Doesn't look low to me. I also cleaned the EBCM ground as best as I could. I know that I do have something going on with my brakes though as I seem to have a warped rotor or at least I used to? If I brake from a higher speed the truck will shake pretty good and as I am rolling forward on the brakes I will get a 3/4 turn of normal movement and then 1/4 of slowing down as if the pads are running over a hump. I have had this issue all year round though, so I believe it is unrelated.

Mods...
The only electrical mods were all installed after last year's battery replacement and are as follows:

• HID low beam retrofit.
• DSP5 switch
• LEDs in the cab
• USB-C charger to replace the 12-volt outlet.

The USB-C charger is suspect, but I can't believe it would nuke a battery and then the only time the message shows up is a year later. I hit much colder days last year after replacing the batteries and I never had an issue until now.

If anyone has any suggestions, please let me know. I will make it a point this weekend to check for codes as well as to drop my batteries off.

 

[2004LB7]

You might need to clean the mounting surface of the ABS sensors to free them of rust and debris that can cause the sensor to not read the tone wheel correctly

As for the EBCM ground, you cleaned the one under the driver door on the frame cab mount, correct?

 

[johnmyster]

I get that message if the ECM relay under the hood happens to be pulled when I turn the ignition on. That relay is triggered by the ECM during run or start and feeds additional power to some things that need to turn on. Truck won't run without it. Same message, but may or may not be related to your problem.

Could be the ECM is looking to communicate with your ABS computer and can't, so you get the message. Perhaps you've got an electrical supply or ground issue.

Or maybe your LEDs and HIDs are causing electrical interference on the serial communication lines.

Or maybe your ABS system has a stored fault for a test it failed, and it alerts you at startup but not thereafter. The older ABS units were bad for cold solder joints on the controller board. (I don't know if they fixed it by 2006.) I had it in my 2000 and fixed it. You might have a temperature dependent bad connection. That one threw a code but I had to get a scanner that could communicate with the ABS module to pull it.

You need an actual voltmeter and not the dash gauge. Healthy batteries, key on engine off, should be right at or above 12. This time of year, glow plugs and fuel heater could be dragging it down before the alternator is supporting (engine on).

 

[shakenfake]

@2004LB7 Correct cab mount driver door. I’ll have to look into doing the ABS mounting locations. That sounds like something I should do when I do my brake job correct?


@johnmyster That’s some pretty wicked interference if true. Considering I had this message last year I’m sort of doubtful of that as well. I’m thinking along the lines of supply or ground issue.
Correct, dash gauge is not very accurate. I will have to get the voltmeter out.

When I test these batteries should I be testing them one at a time? Meaning undo the terminals at each battery. I don’t want to get false readings and I’m not too sure on it.

Also to test the battery does it matter if I test it right after driving or should I be letting it sit for a few hours?
Noob questions I know but just want to get it right.





I should include I do plan on replacing all pads and rotors as well as doing a brake fluid flush here soon. Whenever I can get the truck into the shop, gotta finish a car first lol

 

[johnmyster]

I can almost guarantee that the message is not related to needing pads, rotors, fluid, etc.

ABS module is under the cab, under the drivers seat. Ground location is likely on the frame near drivers front cab mount.

Places like AutoZone and Pep-Oreilly should have a scanner that can check for codes in the various modules, including stored brake codes.

Healthy batteries should be able to support 12V with a little bit of load on them, like key on, engine off, headlights off. Glow plugs would probably tend to pull healthy batteries down some, maybe as low as 11 if the batteries were really cold.

 

[shakenfake]

@johnmyster Sorry for the confusion, I do not believe the message is related to needing brake parts. Just something I need to do on an old truck anyway.

Yes, I think that is the ground I cleaned off last night.

I have multiple scanners, Autel MK808 is what I am using currently. I did get a J2534 the other day, but I haven't cracked into opening it and using it. Last time I checked I saw no codes in the entire truck except for my heated seats (one of the elements is done).

Okay cool, that is kind of what I thought.

 

[2004LB7]

@2004LB7 Correct cab mount driver door. I’ll have to look into doing the ABS mounting locations. That sounds like something I should do when I do my brake job correct?

It would be easiest to do it then as you'll have most everything off that you need to gain access to the sensor hole

 

[shakenfake]

Partied way too hard last night so no battery test nor truck work today. Tomorrow hopefully.

 

[shakenfake]

Finally tested the battery voltage. Key off doors open it tested 12.3 I believe, other battery did not get a read on it. Think that I didn't have the probes on the right spot.
Key on engine off the battery dropped down to 11.8. Secondary battery was 12.6. I am thinking I need a new battery up front.

Should the batteries both be same voltage all the time even if one is bad?

 

[johnmyster]

Should the batteries both be same voltage all the time even if one is bad?

Yes. The cables running between the battery parallel them.

Unhook one battery and try to start on the other. Then swap. Your truck should start on either battery unless it's cold or the batteries are weak.

Bad ground to the passenger side is my bet. If you're only running on one battery, the other will be low because it's not getting charged, used, etc.

 

[shakenfake]

My main battery is the one that is low, near the fuse box. My other battery is not low.

So, I will unhook pass. battery try to start. Then I will unhook the driver side battery and try to start on the passenger side. NOT physically move batteries or yes physically move battery.

I will have to try and make a ground for that passenger side battery. ACDelco cable is wildly expensive.

 

[2004LB7]

Shouldn't be any difference between the batteries while they are connected. Unless you have a bad connection or badly corroded cables/ground. I'd double check the cables to make sure

 

[shakenfake]

@2004LB7 Should I cut away the insulation on these cables or how should I really check them? The bolts/terminal connectors looked okay but I can double check them for sure.

Sorry if these are all noob tier questions. Though I have some knowledge on electrical this is slightly out of my wheelhouse.

 

[2004LB7]

I wouldn't unless you see something that looks bad. Like corrosion. If they look good the maybe clean up the bolted connections on the other end of the cables

But also do your battery check that you mentioned. Or take them in to get tested

 

[shakenfake]

I do have another Group 78 battery, two actually, that are known goods as well.

But I will check them out

 

[shakenfake]

Took driver side battery to O'Reilly and it tests good. However, I took it after going for a drive where it got charged up so could it have skewed the results? I don't think so. I do plan on taking the passenger side in as well.

Here is a question, so batteries are obviously testing different voltages when sitting however after a drive the batteries are the same voltage. Why is that?
This seems to be an issue when it is cold and not when it is warm. This also only seems to be an issue when the battery is IN the truck. I let the battery sit out last night and it is still fully charged come morning.

So now I am thinking either grounds or parasitic draw. However, I don't think it could be parasitic draw because it would be doing this every time that I start the truck not just depending on temperature.


I also will need to replace my driver side battery bolt on the positive cable. It is shot, can't get a wrench on it anymore. I have ordered some new bolts from Schumacher and will go ahead and swap it out.

 

[2004LB7]

Supposed to test the batteries when fully charged

Batteries in the vehicle connected up should read the same voltage as they are connected in parallel. But if you have one that has a dead cell and is running really low then the good battery will discharge into it. Depending on the health of the cables, grounds and connectors there could be some measurable voltage drop from one battery to the other as they try and balance the current.

Best to pull both out, or at least disconnect them after fully charging and let them sit overnight and then check the voltage. If one sits at less then 12 volts then it probably has a shorted cell. A good battery should be mid to high 12's. This test doesn't measure the internal resistance or capacity though. Either a dedicated tester or doing a load test with a calibrated amp draw will do that. That's why I bring mine to the auto store as they have those testers.

Cold batteries have lower voltage and capacity. The internal resistance goes up and they have a harder time delivering the needed current. But a healthy battery shouldn't have any issues down to freezing temperatures and normally even single digits

 

[jlawles2]

My LLY did that a few times along with service 4WD when new and under warranty. Dealer added a ground strap from the cab to the driver side cab mount and I have not seen the message since.

 

[shakenfake]

I will keep you posted on what I find. I will get my other battery charged and then let them both sit out overnight.
My battery bolt should arrive today, so I'll also get a chance to see if that fixes anything at all. I doubt it but that bolt is very rounded off.

 

[Chevy1925]

So. Have you pulled the actual codes? If you get that message, you have codes in the ebcm. I’d start there before throwing money at it