330: And All Through The Shop, Not A Creature Was Stirring... Expect For This Hungry Mouse

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Hey, what's going on, Automotive World?

Welcome to another episode of the Automotive Diagnostic Podcast.

My name is Sean Tipping and I'll be your host once again for this week's episode.

Thank you so much for joining me.

Just me on the show this week and I am going to be talking about mice this week

on the show.

Yeah.

Rodents, it's usually mice.

You see this a lot on vehicles where there is rodent damage to the electrical system.

It's usually wiring.

I'm sure everyone out there, if you've been in this industry for any period of time,

you've seen the same thing.

But I had a really interesting one this week.

Because of the damage that was done, how it was done, it created a very interesting

problem and it got me thinking about some of the other rodent damage vehicles

that I've seen over the years where, I mean, number one, it's usually an open circuit,

but sometimes can be a shorted circuit or in the case of the one I dealt with this week,

it was open and shorted, right?

So you didn't have power where you expected to have power and you did have power and

another wire you didn't expect to have power on.

So obviously those can happen and it's, you know, not a huge mystery once you

find where the damage is, you can see it pretty plainly.

The thing about rodent damage to wiring is that for the most part, it is going to be a

unique one-off scenario that you may never see that exact fault on that type of vehicle ever again.

Now, that's not 100% true.

And I'll give you an example because, of course, there are specific areas in the vehicle

within components that might attract a rodent, right?

They are going to go for the small spaces that are maybe contained, a place where that they feel

that they could build a nest, right?

And they do they bring in stuff and you can see the like padding from or insulation or

nuts and seeds and, you know, things like that, you'll see little nests.

But then wherever they pick to make their home, they end up chewing on wiring and somehow

or another, it always ends up being the can wires, it seems, that they go for.

There was an issue with, I think it was either Toyota or Ford where they had like a

soy based insulation on their wiring and it was almost like attractive to rodents and so

they were chewing up the insulation like crazy on these.

But I mean, again, we've been seeing this for years.

This is nothing new.

Of course, up here in Minnesota, it seems to happen in the winter time even more

so because of course, they're looking for a nice warm place to spend the winter and

hey, under the hood or in the cab of the vehicle is a great place to make a little mouse home.

So of course, chewing wiring, we're going to have issues and that's what I'm going to be

talking about today.

But also just kind of the uniqueness.

Now, let me start off actually with one that I thought this was pretty crazy that

the mouse ended up chewing the same wire on a similar truck years apart.

So I'll give you the scenario and actually I don't even have the exact year.

I think it was around a 2010 ish Ford F-150 and it wouldn't start and you couldn't

communicate with a number of control modules.

It was the ABS, the PCM and I think the airbag control module, maybe one other one.

So there was four or five different modules you couldn't communicate with.

And you know, you could look at the live network thing and OK, all these modules are

offline and I ended up finding, OK, what do they share?

They all share a power feed from a run start relay that's in the fuse box under

the hood. And this is the old style where that fuse box is like right front

and center under the hood when you open it up kind of over the top of the fan

shroud. So relay in there, body control module operates, it turns it on, it sends

power to these other modules. And interestingly enough, this is hindsight.

I was actually putting this together for a network class that I presented.

But you could actually see on the CAN bus networks that these modules lived on

where, you know, they should be communicating, but they're not.

You could actually see the bias voltage of the network be lower than where

you expected. Now, this is kind of a networking thing, but I just thought I

pointed out because you can see it plain as day when these modules are not

receiving the power feed that they need, but they're still on the bus like

physically connected. They'll actually drag that bias voltage down below

two and a half. It's just something to pay attention to, right?

If you see your bias voltage on your CAN bus network is not at two and a

half, you know, it's significantly elevated or it's below, you can say,

hey, I might have a power feed issue to a module or modules in this case.

And then the opposite, if it's higher than expected, I might have a ground

issue to a module or modules. And it's not going to solve the problem

for you just by observing that. And I'm sure there's circumstances where

maybe it doesn't necessarily apply to the fix, but a lot of the times it

can at least get you thinking like, oh, okay, I see a bunch of modules I

can't talk to my bias voltage is lower than I'd expect. Do they share a power

feed? That would be the next thing is not like to make that like

determination right on the spot. I definitely have this, but let me

take stock of these modules and see, do they share a power feed? And

then maybe I'll go after that. Now, full transparency. This was back

in like, I think 2019 that I diagnosed this vehicle. So it was

a long time ago, but I had some screenshots of it and stuff. I

wasn't aware of looking at bias voltage. I did not make that that

clarification at that point. I went through the hard way and then I

just ended up checking like, hey, I have all these modules. The

CAN bus pattern actually looked halfway decent. Again, paying

specific attention, you could see the bias is a little low, but

the traffic was still there. I could still communicate with

other things. I didn't seem like I had an open, I think, you

know, 60 ohms on the on the bus that they were on. And I

eventually got to the point that, okay, all these modules share a

power feed found that it was that run start relay, which is

controlled by the BCM. It was not being controlled by the BCM.

There's a single wire the BCM uses to control that relay in

that under hood fuse box, you know, wasn't getting the

signal and found that there was a wire underneath that fuse

box that was chewed through by a mouse. Okay, easy enough to

fix, right? Just patch up the wire and you're good to go. And

it makes sense that the mouse wanted to get into this little

contained space underneath the this fuse box because it's

housed by like a plastic shell. And of course, you got all the

wires underneath the fuse box to all the fuses and all the

relays. And the mouse just decided to chew that one, I

think it was a purple wire. And that was the only one it

chewed, right? And why who knows? That's the one it picked,

though. Now, fast forward about four years. This was 2023. 20.

Yeah, I think it was I think it was 23 that I looked at another

Ford F 150. And the funny thing was this was about a mile from

the first shop that I made that diagnosis on. It was in the

same town, different shop, different truck, but very

similar, like the same setup. And it had the exact same modules

that were offline. And I remember, like looking at it, because I

had made a case study out of the first one. And I remember

looking at I'm like, Oh, hey, I remember all these modules.

And this time around, I had been through some classes, got

some information. And I did notice that can bus voltage was

like, Oh, it is a little low. And the last time I had this,

it was, you know, that run start really not providing

power to the modules in question. So I go and I find and, okay,

I'm not getting a signal to that relay. And I pull up the bottom

of the fuse box, and a mouse had gotten into the bottom of

fuse box and chewed up that one single purple wire again. Now,

again, different truck, I'm assuming different mouse, different

shop, but exact same wire chewed underneath that fuse box.

So I guess I'm putting this out there to say, my my

episode idea was wrong. Sometimes they do pick the same

spot. How often that's going to happen. I don't know. But I

thought it was pretty funny that the exact same problem

happened to the it wasn't a host of wires. It was just one

wire that the mouse decided to choose. Does it have something

to do with the color? I have no idea. Anyways, that was

interesting. But obviously, we've seen mice get into, you

know, things like underneath fuse boxes and stuff and chew

up wires. Now, that's just an open circuit, right? And there's

nothing really that special about finding an open circuit,

right? It's identifying the circuit that you have a problem

with, identifying that, hey, it's open, and then it's

finding the open that, you know, generally makes for a

fairly boring podcast to just tell you about finding open

wires. Okay. But sometimes you can have other things

happen as they chew through multiple wires, you can have

a short between two wires, right? And like I mentioned,

they seem to pick the can bus wires for whatever reason. Maybe

it's that mice chew other wires, and they're less critical

circuits, and customers don't bring their vehicles in if

some minor thing like a, you know, a switch for a dome light

doesn't work or something like that. They're just like

whatever, but a can bus line that's chewed is going to

disable the vehicle. So we see those more that might be why

that seems to be the case more often, but somehow or

another, they always seem to find those can bus wires.

Maybe it's a twisted pair. I don't know. Anyways, I had a

Ford Escape recently, where that was the case. Not only did

they chew through the can lines, but they shorted them

together, right, because they're pulling those little

copper strands apart. And then they kind of just leave

it in a mess. And then those wires are touching

together. And when you have a shorted can bus,

obviously, if you own check between the high and the

low side, you're gonna get zero ohms, not OL, not

120, not 60. You have zero. It beeps if you have it on

the continuity setting. And that is a short together.

If you scope a shorted can bus, and many of you have

seen this, it's pretty much going to be a flat line.

Now, not perfectly. You'll if you look closely at the

line on your scope, you'll see just a little bit of

movement off of that bias voltage, right, you're

going to have two and a half. And if you zoom in on

it, you're like, Oh, that actually looks like what

could be a can packet. Now, it definitely doesn't

look right. There's not much movement off of that

bias, but you'll actually see a little bit of something

even they're shorted together because the modules

are still trying to communicate. But with the

high and the low shorted together, they cancel

each other out. So it's not usable. You can't

talk to anything. That was the case on this

escape. And, you know, nothing real special

about this. I just basically broke the network

down into sections and followed where that short

was it ended up being underneath the battery

tray. There's a harness that runs near the ABS

module and the can lines are right on the top of

that harness kind of exposed actually. And of

course, the mouse does a great spot for the

little mouse underneath the battery tray on this

harness got hungry chew the wires. That sort

of stuff happens as well. So that went now

I'm going to get to the interesting car

here. And again, you know, spoiler, it's

thrown damage. But I thought the way that the

symptoms presented themselves were pretty

interesting on this one, you know, learned a

little bit about the car. Will I ever see this

exact same problem on this car? Again,

probably not. Because it was a real specific

way that the mouse chewed through the wires

that allowed this to happen. So this was a

2019 Toyota Corolla. And the issue that

they were having was once you start up this

vehicle, and sometimes you had to drive it, but

it would happen pretty frequently, you'd shut

off the vehicle and the HVAC controls in the

center of the dash would stay on and you can

control the HVAC system indefinitely or until

the battery died. And you could take the key

out of the ignition. This was a blade style

key on this one. And obviously the car

shuts off, but that HVAC system keeps

running, drains the battery, but you could

operate it like the key was still on. And the

shop had been through this and they replaced a

few things, trying to get this resolved. But

they're really busy and they just didn't have

the time to, you know, dig into this fully. So

we take a look at it. And at first it wasn't

acting up. But they said, Well, sometimes

when you drive it, it happens and it's pretty

consistent. And they actually just hopped in

it, took it around the parking lot, and then

shut it off. And then it was acting up. So it

didn't take much to get this to happen. And so

then it's in the bay, key is off and verify

HVAC controls are on the little screen. It's

an automatic system. And there's just, you

know, a few things on the screen. You can

control everything. You can run the fan.

Actually, he had the fan unplugged so that

it wouldn't completely drain the battery.

Hey, have you ever been faced with the

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enough. But anyways, we get into it

and they had already replaced the AC

amplifier because he did note that

when the AC amplifier, which is the

control module that's really in charge

of the HVAC system, you have the

display screen, but that is just for

controls. And it links on a Lin bus to

the AC amplifier, which is really in

charge of, you know, making decisions,

making things happen within the HVAC

system, including controlling the

compressor. And they had replaced the

AC amplifier with a used one because

when he unplugged the AC amplifier,

he said, then you can no longer

control the HVAC, the screen went off

and the drain from the battery went

away. Now that is somewhat normal,

right? If you had the car on and you

unplug the AC amplifier, the screen

would go off and it would stop

working. But it seemed to be that

there was something to do with that

module, but replacing it didn't do

anything. It had the exact same

situation even after a placement.

But it was a good direction for me

to start with is like, maybe I

should be looking at this, you

know, what changes does unplugging

the module really get rid of the

problem? Or is it just disabling

enough stuff because that module,

you know, operates a number of

things within the HVAC that seems

like the problem is gone. That's

what I have to determine on this

one. Scan it. No useful codes in

it. When the key is on, everything

seems to work the way it should.

But of course you have a bunch of

stuff working that you wouldn't

expect it to all the key is off.

So I go to the AC amplifier,

which is in the center console

area near the accelerator

pedal. And I start looking at

the circuits that are connected to

it. And it's pretty straightforward

as far as how this thing actually

gets powered up and operates.

It's got a constant battery feed,

obviously a ground, and then it

has a switch technician feed.

And that's it. And so that switch

technician feed needs to have

power in order for this module to

turn on. If that switch

technician feed is off, that module

should not be on. And OK, so

it's a blue wire. I checked the

blue wire. It has power when the

key is off. That's why this is

on. OK, well, that should be pretty

straightforward. Now, where does that

come from? And why does that

power on there? That's the next thing

that I have to figure out. So go to

the diagrams right there, shows

it as the heater ignition fuse

in the fuse box that's right

there underneath the dash. It's a

10 amp. And of course, that has

power as well, along with this

blue wire. So the

question now is, is power

being fed to this fuse

and then to the module and the

other things that this fuse

actually powers. There is four

different legs off of this

heater ignition fuse. It goes

to the control assembly on the

dash. It goes to the AC

amplifier. It goes to the

compressor relay and a couple

other relays under the hood as

well. So this powers up a few

different things. It's not just

the AC amplifier. And so that's

what I'm trying to figure out.

It's like, OK, I have power on

this fuse when the key is off.

Now this fuse gets fed from

an ignition relay, which is

located within the

fuse box that's under the dash,

right? So it's like a junction

block. And it does have like

a BCM that's

plugged into it. But the box

itself isn't a module, but it

has internal relays.

And one of those internal

relays is an ignition relay

that is controlled by the

ignition switch and then sends

power to this fuse when the

ignition is turned on.

So that's my question. OK, is

power getting fed to this fuse

and then going to these

components or is

something on that circuit,

one of those four legs

shorted to power and power is

backfeeding to everything else

keeping it on. It's one of

those two options. So that

is fairly easy to figure out

in a situation where you have

a fuse and it has power on

it when you would expect

there to not be power on it.

Pull that fuse in the state

where you would expect power to

not be on it key off and

then check both sides of the

fuse. Right. So what I mean

by that is you have two

terminals once you remove that

fuse and you can use your

test light and figure out.

OK, do I power on one or

both sides? You probably are

only going to have it on one

side. And then you could

turn the key on because you

might say, well, I don't

know which side this goes

to. But you could figure it

out with the test light.

Right. I could go over to my

AC amplifier and that

leg that comes out of the

fuse is going to go to pin

one. It's a blue wire.

If I remove the fuse, do I

still have power on that blue

wire? OK, if I do, I

know for sure it's not

coming from the ignition

switch. And then I can go

up to the fuse. I can test

both sides. One should have

power. One won't.

That's probably the ignition

feed side. I could turn the

key on and then I should have

power on both sides of the

fuse, right? So you can use a

little bit of logic there to

figure out, OK, that side of

the fuse goes to the

components. That side of the

fuse comes from my

ignition relay, which again

is internal to this fuse

box. So I figure that out

and it is on the component

side. OK, so key off, got

power on the fuse, remove

it and everything stays

on at that point. Even if I

pull that fuse that does

not disable DHVAC system.

So I mean, right there, you

know, even without using a

test light that like, OK,

power is being

shorted to this circuit

somewhere somehow. But I got

power on the component side

of that fuse. I have power at

my AC amplifier. And I'm using

that kind as a test just

because it's easy to access.

And I'm just back probed

into that wire right at the

AC amplifier. Now, like

he said, if you unplug the

AC amplifier, it seems like

everything turns off. And I

verified that I unplug the

AC amplifier and I no longer

have power on that blue wire.

OK, so fuse could be out, fuse

could be in doesn't matter at

this point. I put everything

back in. But I have power

on that blue wire as long as

the modules plugged in. I

unplug the module, everything

shuts off and I do not

have power on that blue

wire anymore. So I don't

really need to look at the

other components and I

didn't. I'm focused in on

that AC amplifier. Now

that again, they already

replaced it with a used one.

First one did the same

thing. Is it possible? This

is a common issue with these.

I'm not sure. Is there

something else that could

be shorted that's feeding

power through the module onto

this circuit? That's a

question that you have to

ask yourself. I mean, it's

a lot of cases when you

unplug the control module and

it fixes your issue.

Sometimes it's a control

module, right? Maybe

something taken down a

can bus or in this case

where we're, you know, we

have power shorted to a

circuit, you unplug the

module, it's no longer

short of the circuit.

Maybe it's the fault of a

module, but maybe

there's a short somewhere

that's feeding through the

module onto this circuit.

And it's something you have

to consider. How do we, how

do we figure out if that's

the case? Now what I

did here was I looked

at the circuitry on

the diagram. And of

course, I should only have

two power feeds into this

module, one constant, one

switched. But that's it.

I should not have any

other 12 volts go into

this module at any

point. But when I have the

thing unplugged, if I go

across all of the pins and

just touch them with a

grounded test light, only

one of them should light up

unless I have the key on

then two of them should

light up. And like I

mentioned, when the

module's unplugged, I no

longer have power on that

blue wire. So the

power, the B plus

is actually coming from

the module onto that

circuit, but from where.

Okay, now I do have it on

my white wire, which is

my constant. I would expect

that. Okay, that's normal.

That's not a problem. But

do I have it on another

circuit? And I do. And

actually, it's real close.

It is one pin over from

the blue wire. So the blue

ignition feed, where I

have power, I don't want

it. That's pin one. And

pin two is a light green

wire. Where's that go?

That goes right to the

solenoid on the

compressor. Okay. So this

is the power feed. And

it's a solenoid plus.

But this is the power

feed to the compressor

solenoid that the AC

amplifier is going to use to

operate this thing. Now,

there should not be power on

this wire unless the AC

amplifier is sending it

there. But for some reason

there is. And this is module

unplugged, right? So pin two

light green goes straight

to the AC compressor. I've

got power there. Then you

plug it in. I still have

power there. And then I

also have it on the blue

wire. So my guess is here

that this power that is on

this wire should not be

there based on the

diagram. A solenoid on

compressor shouldn't provide

that. But it is and it's

backfeeding through the

module onto the ignition

circuit, which is keeping

the HVAC system awake.

Okay, so now I figure out,

okay, why do I power on

there? And I go immediately

to the compressor once I

see this. And turns out

it's already unplugged. And

I asked him, he's like,

do you unplug the

compressor? He said, yeah,

it was one of the things I

was looking at to see if

it had anything to do with

it. And I just left it

unplugged. Okay, so

compressors unplugged and I

got power there. So it's

definitely not the

compressor itself. And I go

to the light green wire on

the compressor with my test

light and I don't have

power there. So I double

check the diagram I

actually pulled up the OE

diagram. I had a Toyota

sub. So I used Toyota

service information to

make sure that like the

diagram wasn't wrong. And

it's the same color

wire. But I look, okay,

this is this is the wire pin

to does go to the

compressor on this circuit.

But I have power at the

module, but I don't have

power at the compressor.

Well, there's two other

connectors in this circuit

between the AC amplifier

and the compressor. So I

got to find these

connectors, and then I

can break up the circuit

and figure out, well,

number one, why do I

power one spot, not the

other? And then is

there an open and a

short? That's what it

would seem to be unless I'm

still misunderstanding the

diagram. But let's go to

these connectors, break it

down, see what we can

find. So there's a six,

which is located under the

dash on the passenger

side, just before the

harness leaves the cabin

to go under the hood. And

there is BA two, which is

actually located in the

underhood fuse block. And

these are both pretty

easy to access the one

under the dash, you just

have to reach underneath

there. Finding them was a

little bit of work, but

once I found them, they're

easy enough to access. So

a six under the dash, I

unplug it, and I have

power on the side that

goes under the hood, right?

So this is a connector

between the AC amplifier

and the compressor under

the dash, I unplug it. And

if you look at the

diagram, you can see the

male female side on the

diagram. So you know

which direction you're

going, right? If I touch

it with a test light, it

lights up on the female

side, I look at the

diagram, female side goes

towards the fuse box and

the compressor. And I power

there. Okay, so I need to

go under the hood. So I

look under the hood, there

was evidence of rodents

being under there. They

had chewed away some of

the padding on the

firewall. They had a

little nest underneath

the intake. So right

there, and I think the

tech had even mentioned, he

noticed that there was

some evidence of rodents

under the hood. But I

follow the harness, it

leaves the firewall, goes

across the firewall, goes

under the air box, and then

over to the fuse box. And I

look it over and I don't

see any evidence of the

rodents actually damaging

the harness there. Now, it

could be underneath

something, maybe I don't

see it, but it's not

visible in the part of

the harness that I can

see. So then I go over

to BA2 connector, which

is in the under hood

fuse box. I disconnect

that, I don't have

power on either side. Okay.

So somewhere between that

connector under the dash

and the fuse box, I not

only have an open, but then

I have a short to power on

the side that goes towards

the cab of the vehicle. And

this is where we were

talking about it. And I was

like, Hey, I think we

should pull this fuse

box up and look underneath

it because it's very

strange that I have a

short to power and an

open here. So he

yanked up the fuse box

which took a little bit

of work to pull some

things apart to get

underneath there. And as

soon as he did, he found

at the bottom that light

green wire had been chewed

along with another wire

which had constant power

on it. And it was touching

that one. So basically it

opened it up in the

direction of the compressor,

but it shorted it to power

in the direction of the

AC amplifier. And that

wire having constant

power, the power wire

for the compressor

solenoid backfed through

the AC amplifier onto

the ignition circuit, which

kept that module and the

screen and everything with

the HVAC activated, even

when the key was in the

off position. So again,

rodent damage. Will I ever

see that problem again?

Probably not. I mean, I

guess it's good to know

that that sort of thing

can happen. And that's

what I'm taking away

from it is when you

have something like

this, right, power

shorted on a wire, you

unplug a module, it gets

rid of it. It's not

always the module, right?

It can be another circuit

connected to that module

that is not normally

supposed to have power,

but it does. And that's

going to backfeed through

other circuits. So just

be aware of that. If you

get to a part of like, hey,

this module is bad. I think

it's the cause. Double

check, use some logic.

Look at the wiring

diagram, like, okay, which

wire should I have power

on? Do I have power on

those? Do I have power

on any other ones? If I

do, and I don't expect

power to be there, why

is there power there? And

could that be causing

my problem? Same thing

could be true of a

ground, right? Where you

could have five volt

reference shorted out

that's taking down a

control module, preventing

it from talking. And we've

talked about it before

where, you know, you have

a whole network taken

down because of a module

that has a bad ground,

right? We remove that

module from the network

and now I can talk to

everybody else. But you

plug that module in and

you can't talk to

anything. Or is it the

module? Okay, is it

potentially a, you know,

a bad ground to that

module that's causing

that to happen? It does

happen, right? So I guess

it's just a good reminder.

But those mice, those

rodents, they definitely

keep you on your toes

because you're going to

see these unique one-off

problems that you can't

really use pattern

failures to find. You just

have to use your, you

know, basic electrical

diagnostic skills in

order to get to the

solution. So I thought

that was pretty

interesting. Wanted to

share it. That's all

I got for this week.

Thank you so much for

listening. Always

appreciate it. But with

that out of the way,

let's get out there,

start fixing the world

one car at a time.

330: And All Through The Shop, Not A Creature Was Stirring... Expect For This Hungry Mouse

Ford F150

Ford Escape

Toyota Corolla

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