Instrument cluster lights turn off when map light is turned on

[dkad260]

So today I removed and cleaned the grounds in the rear of the vehicle, this was the before pic but now they are all cleaned up just in case.

The LR parking sensor is the one that is bad and was hit about a year ago and I only noticed occasional errors when it rained starting a few months ago, and could be key to all this. The sensor is damaged and I checked the resistance to ground along the low signal circuit which is ground and I have 15 ohms to ground which doesn't seem good.

I also checked the grounbd at the LF dash which is either G201 or G201 but from this post...

to the overhead console harness, I have .8 megaohms.

I removed the ground and cleaned it up just in case.

I wiggled all the wires and didn't see any fluctuation in the meter. Once the modules starting to I assume fall asleep, I had -1.99 ohms on that same circuit.

Will dig into it more tomorrow, but really starting to look like the BCM as I don't see where I would have a broken wire but so many things on this circuit and I really need to pull the bumper cover and check for any pinched wires.

 

[dkad260]

I want to clarify the above post .

I had almost one mega ohm with the ground wires at the dash pillar bolted to the stud. iit was when I removed the wires from the stud and measured directly from the ring terminal to the overhead console.I had -1.99 ohms. Would that suggest there's a small voltage being applied to that circuit at that point?

 

[dkad260]

Going back and recapping the history, a relative hit the LR of the Yukon about a year ago, not much visible damage but about 6 months after, I started getting DIC warnings about the park assist and thought it was the torrential rain blocking the sensor ...went away after a few min and thought nothing of it, especially since the park assist was still working. A few months later I installed the LED headlight and fog lights.

Those are the only 2 things that come to mind, and I don't think it's the LED's.

I think the water got into the opening of the LR sensor and shorted something in one of the modules, either the park assist module or the BCM, both are linked to the dimmer circuit.

 

[Doubeleive]

So this saga keeps gaining twists...lol. Adding to the edit above I DO have continuity from the NEG bulb terminals to the end of the pigtail of the visors, but my ohms was reading "OL" with the harness connected to the headliner harness...I was basing it off the reading and not using continuity mode. When I unplug the visor, I get .3 ohms from the NEG bulb terminal to the end of the pigtail, but "OL" when reconnected.

I pulled down the overhead console and also checked the ground resistance from the RH body harness for the RH visor and I have 1 megaohms to ground.

With the headlights off, I have 11.1 V to ground at the RH visor harness, but with the headlights on it drops to 8.9V. At the same time if I check the map bulb in the overhead console I have 11.1 V with the headlights off and 10.8V with the headlights on, much larger drop at the visor.

I disconnected the harness at the overhead console and no change of resistance to ground at the visor harness.

Would that amount of resistance be from a relay?

my question is if you unplug those visors. does the problem still occur.
any grounds should be reading virtually 0, if you probe the visor harness (on visor, not the end going to body) it should read OL lid closed, and ) 0.0 ohms lid open or tilted or any other position with the lid open, if it reads ol with the lid open stick a bulb in it or short the bulb clips together.
if you probe the visor harness going to body it should be 12v or whatever the battery voltage is at the time. (that should be constant power, no matter the key position, unless of course you turn it to start then it will drop like everything does to send power to the starter). the visor harness ground should be 0.0 or pretty darn close to it, you noted 0.3 that's about as much you want to see on any ground.
to clarify the visor circuit should be normally open and closed circuit with lid open/bulb installed.

 

[mikez71]

You mention checking the parking sensor to ground, but the parking sensor only connects to the park assist module, there is no ground to sensor.
(Well one end grounds in the module, BUT through some type of resistor, not straight ground.)

You mention checking grounds to overhead console, but the dome light ground goes to the right side of dash. (G200 not G201) What happens when you test one side of dome bulb receptacle to ground? (sorry if you did already, but one side of the bulb receptacle should go straight to ground)

In some cases you maybe testing ground wires through various modules? That could explain your negative resistance.

The dimming circuit going to park assist module is only to ground the park assist indicator light.

Dome lights all get power from BCM, and ground directly. One bulb terminal should ground? If not, check the right side a-pillar ground.
It seems like when you tested the LF dash ground, it should still be less than .8 megaohms through the body sheetmetal to the RF dash ground to the overhead console.. I would check the RF ground forsure..

 

[dkad260]

Before I retested, I verified my meter leads and probe resistance.


Internal using leads:

Leads and probes:

Battery NEG to engine block, I was surprised to see this:

NEG to firewall on LH side

I also have approx 1.4 ohms from G201 to the NEG terminal...however I have .04 ohms from G201 to the RH side metal behind the panel in the door opening.

my question is if you unplug those visors. does the problem still occur.

Yes

if you probe the visor harness going to body it should be 12v or whatever the battery voltage is at the time

Yes, I have 12V at one terminal, and I lose that voltage with the visor tilted, the flap on the mirror doesn't change the reading...I don't have the little button for the mirror flap

the visor harness ground should be 0.0 or pretty darn close to it, you noted 0.3 that's about as much you want to see on any ground.
to clarify the visor circuit should be normally open and closed circuit with lid open/bulb installed.

Mirror ground to G201

Overhead console to G201

Mirror to ring terminal removed from G201:

You mention checking the parking sensor to ground, but the parking sensor only connects to the park assist module, there is no ground to sensor.

Ok, copy that.

What happens when you test one side of dome bulb receptacle to ground?

Pic above but .74 M ohm

One bulb terminal should ground? If not, check the right side a-pillar ground.

Checked and while resistance is not .03 the bulbs do work when the doors are open...but turn off with the button pressed. Also, I gain about 300-400K ohms when I press the map light button.


One more thing for both you and @Doubeleive After a min or so when I guess a module goes to sleep, I get 60 ish ohms to G201...this might be a key clue.

As soon as I open the door, I get the .8 M ohms.

 

[dkad260]

One thing I haven't checked, is the resistance from the NEG battery terminal to the ground terminal at the body under the RH side of the radiator. I cleaned that area this weekend, it looked good, but I cleaned it anyway.

Also, when I checked the resistance from the NEG terminal to G201, block and firewall, I did so with the ground cable connected to the battery...if that matters or not.

 

[mikez71]

Mirror to ring terminal removed from G201:


View attachment 483971

That's G200! (or ground zone #10 in the factory diagram)
And somehow you get more resistance when that ring terminal is bolted down?

And it is weird that your visor flap doesn't activate the switch, I could swear it was the flap that turns the light on... ?
Otherwise just flipping the visor down, the light is on?

Again, it seems like you have enough ground for the dome lights, and hitting the switch only changes the positive side of the circuit...

I'm so confused...

 

[Doubeleive]

Before I retested, I verified my meter leads and probe resistance.


Internal using leads:

View attachment 483965



Leads and probes:


View attachment 483966



Battery NEG to engine block, I was surprised to see this:


View attachment 483967


NEG to firewall on LH side

View attachment 483968

I also have approx 1.4 ohms from G201 to the NEG terminal...however I have .04 ohms from G201 to the RH side metal behind the panel in the door opening.








Yes




Yes, I have 12V at one terminal, and I lose that voltage with the visor tilted, the flap on the mirror doesn't change the reading...I don't have the little button for the mirror flap




Mirror ground to G201


View attachment 483969



Overhead console to G201


View attachment 483970


Mirror to ring terminal removed from G201:


View attachment 483971






Ok, copy that.




Pic above but .74 M ohm




Checked and while resistance is not .03 the bulbs do work when the doors are open...but turn off with the button pressed. Also, I gain about 300-400K ohms when I press the map light button.


One more thing for both you and @Doubeleive After a min or so when I guess a module goes to sleep, I get 60 ish ohms to G201...this might be a key clue.


View attachment 483972


As soon as I open the door, I get the .8 M ohms.

most of those readings are probably dependent upon how good of a connection you have with the probes mine reads anywhere from 1.7 to 0.7 from battery negative to block/head
that 60 ohm reading doesn't seem right though, that's excessive. not sure where the visor circuit leads but I would check from the harness to the bcm and see what it shows.
like unplug that x connector that goes to the visor and check the ohms to the visor that might reveal something, maybe...... could just be a rabbit hole....

 

[Doubeleive]

That's G200! (or ground zone #10 in the factory diagram)
And somehow you get more resistance when that ring terminal is bolted down?

What do you get if you probe the other end of the visor and map light sockets?

And it is weird that your visor flap doesn't activate the switch, I could swear it was the flap that turns the light on... ?
Otherwise just flipping the visor down, the light is on?

Again, it seems like you have enough ground for the dome lights, and hitting the switch only changes the positive side of the circuit...

I'm so confused...

the visor light switch is in the lid, top dead center. same since atleast 2000 with variation, some are slightly different in size & shape.
my wife broke her's on her 2016, I went out to the junkyard and grabbed one off of a gmt900 and made it work, but it didn't work well because the plastic nub part is shaped different and I had to transfer the metal tab over. Did that trying to avoid spending $80 on a new visor (nobody sells just the lid), then I bought a $60 aftermarket one and it worked for about 2 months and started drooping, ended up spending the $80 .
the good news is you can upgrade the gmt900 visor to k2 visor with built in led's plug-n-play, but the light output is not the same and you cannot change the led's in them either.
I guess theoretically you could change the k2's visor's to gmt900 visors if you can find the right color match. the harness is the same and bolt pattern is the same.

 

[mikez71]

Ya I sprung for new visors.. except they were already $100 a piece when I bought them..
Good to know the K2's visors will swap in..

I don't see how hitting the MAP light button can change the ground signal.. But there's a lot of electrical I don't understand..

 

[Doubeleive]

I know when you find it will be ahaa! lol

 

[dkad260]

That's G200

OK, my bad, but the readings were the same on both G200 & G201

What do you get if you probe the other end of the visor and map light sockets?

I get .67-.7 ohms from L to R visor ground, and same from visor ground to console bulb ground

I would check from the harness to the bcm and see what it shows

Will do. I was going to start unplugging each harness as well to see if anything changes but will start with the courtesy lights.

Otherwise just flipping the visor down, the light is on

Been a bit since I confirmed that but when I rotate my visor, I get the circuit to connect through the DMM, same on hoth sides.

the visor light switch is in the lid, top dead center

I had that on my Envoy, but not on these. My visor has 3 cushions, no buttons.

 

[Doubeleive]

the switch is right here not that it really matters unless it's stuck on, as you tilt the lid look closer right there

 

[Doubeleive]

it's pretty well hidden on the gmt900's I think it just has a spring like tab on the k2's pictured below that I modified it needs a metal tab to make the contacts have continuity, my fix failed because the metal tab came off and the clip cracked. I had to grind the plastic a little bit to make it fit

 

[Fless]

Has a comprehensive voltage drop test been done? Great way to verify the main grounds and power feeds.

 

[dkad260]

the switch is right here not that it really matters unless it's stuck on, as you tilt the lid look closer right there
View attachment 483977

OK, on mine it's not visible from that angle, the lid wraps around and blocks it from view.

I did see the contacts on the back side...

When I open the lid, the ground circuit closes, same on both visors....less than
.6 ohms.

Has a comprehensive voltage drop test been done? Great way to verify the main grounds and power feeds.

Not in the sense you are likely describing. I do want to check the continuity from the NEG terminal to the ground near the lower radiator support.

 

[dkad260]

And it is weird that your visor flap doesn't activate the switch, I could swear it was the flap that turns the light on... ?
Otherwise just flipping the visor down, the light is on?

I was messing with the visor the other day and I swore as I rotated the arm, the POS+ circuit would go in and out..but today I did the same and no...just the mirror lid breaks the ground. Sorry if I added even more confusion. I know it would be dumb to have the lights turn on with the visor down and not opening the lid, but it's been awhile since I checked and I thought for sure I was able to repeat that part with the + terminal...my bad.

 

[dkad260]

That's G200

Looking back on post #62, I had -1.99 ohms with the ring terminal removed....I will remove it again tomorrow and double.check that

 

[dkad260]

Today I removed the ring terminals from the LH dash ground and probed directly to the ring terminal and the ground in the overhead console.

I logged the event with my DMM and I could hear a module shut down at approx 25 seconds, reducing the ohms to about 360 ohms then another shut down about 15 seconds reducing to 210 ohms, then then about 5 min later it settled around .4 ohms. This seems to follow the modules falling asleep but which ones and how could they add resistance across all the modules...or is it the BCM at the root.

Here's the graphs and data, not the best sample forms but not too hard to depict. If I swap the leads I don't have the negative polarity but the values are the same.