How To: Strange electrical issues with 14-18 Sierra/Yukon? Do this test first!

[tlaw91]

Strange electrical issues? Random codes appearing? Truck going through batteries?

 

May be your battery cables.

 

Here’s how to check them.

 

You’re going to need:

 

-A digital volt meter set to mV

 

-An assistant

 

[tlaw91]

Step one

Have your assistant put your truck in ‘clear flood mode’

To do this your assistant will need to depress the brake and accelerator pedal all the way to the floor.

What this does is turns off the injectors, so your truck will crank and crank and crank and not start which is how to perform this test.

[tlaw91]

Step two

Let’s check the positive mini cable first

Put your meter between the bolt on the positive mini jumper cable and the end of it where it bolts onto the battery fuse block.

Have your assistant crank the truck (or press the start button) while having the truck in clear flood mode as previously discussed.

If the mV reading is around 100 or more, needs replacement.

[tlaw91]

Step three

Ok now we’re onto the negative cable.

Put your meter between the start of the negative cable at the battery and a good ground. I personally use the 15mm alternator mounting bolt. I’ve taken off the air intake for this photo but that isn’t required.

Have your assistant crank your truck again in clear flood mode.

This test, anything close to or over 200mV fails the negative cable and it would need to be replaced.

[tlaw91]

That’s it.

Try this test hot and cold. Or if you’re lucky try the test when your truck has just been acting up. Most likely you’ll find one or both cables fails the test, and you’ll have an explanation for why the truck has been acting strange.

Examples:
Service power steering
Random U code DTCs
Low battery message with good battery
You keep replacing batteries and alternators
Slow crank randomly
Door locks cycling randomly
Radio screen randomly blank
Truck not maintaining KAM or ‘keep alive memory’- so when it sits and you start up it’s like you just disconnected the battery and resets the window learn and HVAC setting and things

I hope this helps!

-GM technician

[rav3]

Thanks for this post. Good info.

 

Question:

How do you keep the truck "IN" clear flood mode? (Is this keeping your feet on the brake & gas pedal?)

 

Is there anything special to get out of clear flood mode? (Just foot off of gas pedal?)

 

What is you have another bad ground some where else? Like the (2) grounds in the dash L & R.

 

Or bad body ground that's close to the starter?

 

I'm just curious IF they play into this test? Several videos on Youtube showing these fixes.

 

 

[tlaw91]

Keep both feet depressed on the pedals when cranking.

 

Let off to get out of clear flood.

 

This post is about bad battery cables and how to test them.

 

I’ve never seen bad dash grounds. Never fixed them. And I work on 5-10 vehicles a day.

 

There is no body ground near the starter.

[cooverjosh]

I love people like you thank you for sharing the info [emoji173]

Sent from my SM-N986U using Tapatalk

[2018GMC]

Thanks! 

I have been getting a service stabilitrack on the DIC randomly on startup. Disappears quickly before i can Dismiss. Happens randomly once or twice every few months, only during startup.

[BlaineBug]

I had a very strange electrical issue with my 2019 Yukon that was extremely intermittent.  Upon rare startup not all of the HVAC and dash gauge electronics would work, the transmission would not engage any gear, and the power steering was non-existent.  Also service stabilitrak error, service power steering, etc. errors.  Turning off/restarting maybe a half dozen times would "cure" the problem and then it wouldn't appear again for maybe 6 weeks.  Happened twice to me in January and February of 2020.

Dealership was advised by GM to replace the ECM last March, but simultaneously they also found a major ground on the frame behind the passenger front wheel well "full of undercoating."

Might want to check that ground yourselves as well.  I can see how that would fool you into believing your negative battery cables had high internal resistance.  I'm not ultimately sure which of the 2 issues was mainly at fault, but either way in 9 months I haven't had this issue return (knock on wood!)

 

PS - After receiving my Yukon back in March earlier this year after it was at the dealer for about 5-6 weeks, I investigated this ground connection further and cleaned it up better than the tech did.  Once re-installed I painted over it with black paint on the frame since some of the wax undercoating was disturbed in that area.

I posted a thread about these issues here starting in January 2020, feel free to have a look:

 

https://www.gm-trucks.com/forums/topic/233496-2019-gmc-yukon-no-trans-gears-no-tachometer-no-oil-pressure-no-power-steering-second-time/#comments

Edited December 12, 2020 by BlaineBug

[tlaw91]

That’s your negative battery cable. That’s what you’re talking about.

Frame undercoating for that ground isn’t that big of deal typically because every single truck made has that undercoating.

The better way to repair your truck would’ve been to go ahead and replace that cable. Goes from the battery negative down the firewall then splits into two, one bolts to the block in front of the starter and one goes to the frame where you’re talking about.


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[txab]

22 minutes ago, BlaineBug said:

 

I posted a thread about these issues here before but for whatever reason I can't find it in my subscribed topics anymore.  Maybe it's been quiet for too long?

Look through your posting history, you should find it

[BlaineBug]

12 minutes ago, tlaw91 said:

That’s your negative battery cable. That’s what you’re talking about.

Frame undercoating for that ground isn’t that big of deal typically because every single truck made has that undercoating.

The better way to repair your truck would’ve been to go ahead and replace that cable. Goes from the battery negative down the firewall then splits into two, one bolts to the block in front of the starter and one goes to the frame where you’re talking about.


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I believe the dealership "may" have checked resistance on the cables.  Possibly.  Apparently the only U codes present kept leading back to loss of communication between some other modules on the ECM.  The local techs were in communication with the "escalated" GM TAC helpline and they came to that conclusion.

 

However it doesn't seen normal for there to be undercoating between the ground lug on the cable and the frame.  Shouldn't that be cleaned away before installing the cable?  That's the practice I've always followed when installing a ground.  Make sure paint is ground away between mating surface, etc.

 

Also since it was still under warranty being a 2019 I let them do all of the diagnostic work.  Everyone one the forums was telling me the battery was getting bad - the only thing I did personally was take it to 3 different places to be tested and the battery passed every time.

Edited December 12, 2020 by BlaineBug

[tmo]

What should the cables be testing at if they are good? Below 200 for the neg. and below 100 for the positive? Lower the better?

[BlaineBug]

28 minutes ago, txab said:

Look through your posting history, you should find it

Found it, if you care to have a read.  Not to distract from this thread but perhaps the symptoms and root causes are related.  The electronics in the 2014-2019 Silverado and Sierra are identical to the 2015-2020 Tahoe, Yukon, Suburban, and Escalade.

Edited December 12, 2020 by BlaineBug