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201: 2020 Ford Fusion Intelligent Access Failure
201: 2020 Ford Fusion Intelligent Access Failure
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About this episode
A detailed diagnostic walkthrough of a 2020 Ford Fusion that wouldn't start or respond to its smart key system unless the key was placed in the backup transceiver. The host explains the smart key system's operation, focusing on the body control module (BCM) and radio transceiver module communication via a LIN bus. Using specialized diagnostic tools, the issue was traced to an open LIN bus wire between these modules. The episode highlights the complexity of modern keyless systems and offers insight into troubleshooting communication faults without immediately replacing parts.
Topics:
ford fusion 2020
smart key system
body control module
radio transceiver module
lin bus communication
diagnostic tools
proximity key troubleshooting
vehicle no start
wire harness issues
automotive diagnostics
Cars:
Ford Fusion
In this episode I share the diagnosis of a 2020 Ford Fusion that doesn't seem to recognize the smart key to turn on the ignition or any key-less entry functions. I'll describe system operation and my thought process through the diagnosis.
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"...want to share a diagnosis with you on a 2020 Ford Fusion that wouldn't start and would not key up. I thoug..."
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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 today's episode.
Thank you for joining me Today on the show.
I want to share a diagnosis with you on a 2020 Ford Fusion that wouldn't start and would not key up.
I thought this one was pretty interesting and learned some stuff about this system as I went through trying to figure out what was wrong.
Now this is a smart key system, so you got the proximity key in your pocket or purse.
You can touch the button on the door handle.
It will unlock the doors.
You hop into the vehicle, you press the start button Should key up the dash, start the vehicle.
You can also use the RF functions on the fob, like traditional lock, unlock, trunc, all that stuff.
That's the way the system should work anyways.
The reason I was called in for this one is none of those functions worked.
You hopped in the vehicle and this is their main concern.
You hop in the vehicle with the key and you press the start button and nothing happens.
I believe it said no key detected on the dash or something to that effect, unless you put the key in the backup transceiver.
If you do that, which is in the center console, then you press the start button, the vehicle will power up and it will start, and so that's what I'm called in for.
So, first thing, I do, of course, verify all that is the case, and it is.
The vehicle will only start up if you put the key into the backup slot.
That does tell me that the key belongs to the vehicle, because that could be one of the things in question.
Of course, how did the car show up with the wrong key.
But weirder stuff has happened and I do see some auction cars, so you never know.
But the key obviously belongs to the vehicle, has been programmed to the vehicle because it works in the emergency slot transceiver.
So the next quick check I want to make and I did this honestly, before I even scanned the vehicle for codes or anything like that I just want to see the.
I want to see two main things, and I'm going to use a tool that I've talked about a lot with doing the proximity testing.
It's the diagnostic box tool.
You can use like a key tool max for some of this.
But the diagnostic box, it'll measure the low frequency signal from the antennas, which I'll explain in just a moment here.
But really, what my goal is now that I know the key belongs to the vehicle is is the car reaching out to the key and is the key responding in turn, sending a signal back to the car?
And I'll explain the system in just a moment here.
But that's the check I kind of want to make.
Give myself some direction before I even plug into the car or the scan tool and you can make the argument okay, do the pre scan first and you'll have some information, but this is literally like 60 seconds of testing before I hook up my scan tool and get going with the real diagnostic.
Just give me an idea.
So I do this.
I got my diagnostic box tester, I'm in the vehicle, I've got the key, I press the start button and what I'm looking for is low frequency antennas around 125 kilohertz In the car.
There's one, two, there's four of them total I think it's a center one, a rear one and then they count to two door handles.
But we're looking at the antennas on the interior of the vehicle.
I want to see with my tester is the car reaching out to the key when I hit the start button right?
Is the pressing of the start button triggering the vehicle?
And I don't even know the modules involved yet.
I can assume BCMs and they're somehow.
I don't know the connection.
I just want to know is the car reaching out to the key?
And I can see that on my tester.
It makes a funny beeping noise when the car reaches out to the key when I press the button.
So I do that and it shows up and it is.
It's sending out that low frequency signal from the antennas inside the vehicle to reach out to the key.
Okay, so now I need to see is the key responding?
And you can do this all on one screen if you pick the right test in this tool, so you don't have to bounce around.
It's all done at once.
The key, when it receives this low frequency signal from the car, it's the trigger for the key then to send a signal back to the car, but not those same antennas and not on that same frequency.
It's going to send out.
I think it's a 315 megahertz signal, so much higher frequency signal, and that's going to send it back to the car to say, yep, I got your trigger, I'm here, here's my ID, and then the car takes it from there whether it's going to power it up or not.
So I don't even know the modules involved just yet, but I know that it has to work that way in a smart key system is the car should reach out to the key and the key should then send a message back to the car after it's triggered.
So that's what I'm looking for.
I'm just seeing and that'll give me some direction right, or at least I can keep it in mind as I'm looking at the modules might tell me what module I need to look at.
Of course I'll have to read up a little bit on this particular system to get the details.
But what I see on this thing is, yes, the car is reaching out to the key with the low frequency antennas and, yes, the key is responding in turn by sending a signal back to the car or at least out of the key.
All right, I also found if I press the lock and unlock, I get a signal out of the key as well, but nothing happens in the vehicle.
We don't respond from the button pressing on the fob and we don't respond from the button pressing on the dash, only responded to putting the key into the emergency slot in the center console.
Okay, cool.
So now let's scan this thing and see what's going on as far as codes.
But let's also at the same time, right, I hook up my scanner, I get the full vehicle health report going.
I also want to read up on this system a little bit, just so I understand who's involved and when and what modules I should be looking at, depending on what I have going on.
So quick overview on this one.
It's really not too different, but you do want to understand the modules involved and how they're connected and how you can talk to them, if you can talk to them all that stuff.
Body control module is going to be at the center of this.
When you hop in the vehicle and you press the start button.
This is directly tied to the body control module, which is also the fuse panel that's going to be just ahead of the left kicked panel interior of the vehicle.
It's going to get a signal from the ignition switch that says okay, time to go, somebody's in here.
They're pressing the ignition switch.
The BCM is then going to directly operate the low frequency antennas within the vehicle.
It is hardwired.
There's two wire antennas that the BCM is going to excite and these antennas are going to send a signal out.
Now, these antennas are a one-way deal, right?
The BCM just triggers them, they send their signal out to the key and then that triggers the key to send its information back.
But just so we're aware the key's response does not go back to the same antenna that it was triggered, or at least it's not received by that antenna.
But we go switch BCM low frequency antenna to key and I already know all of this is happening based on the test that I did, all of that is actually working.
So I can say after now I'm reading up on the system description operation okay, well, my start button must work, and I kind of knew that too from putting the key into the emergency slot.
Obviously that works.
My BCM is doing what it's supposed to as far as triggering the key.
Right, because we have a signal picked up on our device and it's recognized by the key outputting a signal.
And I mean that's something too.
If you didn't have the tester for the low frequency antennas, there's a Pico adapter too, but if you didn't have one, you could just measure the output of the key on a megahertz frequency, whatever it is 433, 315, 900 something, whatever it is.
You could measure the response of that key that way and say, okay, every time I hit the button on the dash, the key sends out a signal.
It is probably working, right, not conclusive test, but it's pretty close.
Anyways, now I want to understand where is that information from that key going?
Because all that's happening in this particular 2020 Fusion the signal that comes out of the key is going to go to the radio transceiver module, and this is above the headliner, directly above the rear driver's seat, right.
So the person sitting in the back behind the driver.
If you looked straight up you'd be right under the radio transceiver module.
So you have to pull the headliner down to get to this and the module is glued to the headliner.
So kind of a pain.
If you got to change this thing You're also just getting to it as kind of a pain because you don't want to crease the headliner.
But that's where it is.
It's above the headliner back there and when the key sends its signal out whether you're just pressing a fob button or you're pressing the ignition start button that high frequency signal is going to go to the radio transceiver module.
That radio transceiver module is going to receive that key information, the key ID, and that radio transceiver module is connected to two networks on this and it's important to notice on the medium speed CAN bus so you can actually talk to this thing with the scan tool and get codes out of it and data stream and all that good stuff.
But it's also directly tied to the body control module on a single wire LIN bus that just goes between the body control module and the radio transceiver.
That's it.
That's all that's on that particular circuit.
And if you read the description operation and forward service information.
It's actually pretty descript in how this works.
As far as what I want to know is how or on what circuit or network does the radio transceiver module send the key information to the BCM?
Because that's kind of where I'm headed with.
This is like I'm getting a signal out of the key.
Of course I want to see does the radio transceiver, is it able to receive that message?
But then how does it get that information to the BCM?
Because, with doing some reading and testing on this car, the radio transceiver module will take a key signal and it will send.
It is supposed to send it to the BCM, but the radio transceiver module does not care about the key ID, meaning that as long as the key is the correct type of key for the vehicle right, pretty much any proximity key for 2020 fusion is going to be the right.
You know frequency and FCC ID it's going to take that, it's going to transmit that information.
So you could take a key from a different car, go to it, hit, start hitting buttons and everything, and it'll receive that signal and it will send it out.
Again, I had to read up and do some and do some testing to confirm this, but that information then goes to the BCM, and then the BCM decides whether or not this key is correct for this vehicle.
Now again, going back to it, I'm pretty sure that the key is correct for the vehicle, but I also want to know how all of this works together.
But the radio transceiver module is just there to take key signal from one that does belong to the vehicle, and then it sends it along.
I want to know how, though and if you do some reading the Lin bus, the single wire that is between the radio transceiver module and the body control module that's where the information of the key ID is sent right.
So the radio transceiver module is on the medium speed can.
The key information is not output onto the medium speed can from the radio transceiver module.
It's only going to be fed through this Lin bus to the body control module, all right, and then the body control module decides from there okay, is this the right key, and it moves forward with the process.
Cool.
So before I even scan this thing, I have an idea of, maybe, where I'm going right.
I got to look at this radio transceiver module.
I got to see if it's you know seeing a key is present in the vehicle and if it is now I've got to look at the connection between the body control module and the radio transceiver module.
All right, so full scan.
There are two relevant codes to what I'm looking at and I did have to actually get the vehicle started to do a full vehicle scan.
Right with the key off, you only have limited modules that you can communicate.
I wanted the whole picture, so I started the vehicle with a key in the backup slot and in the body control module there's a U code for missing message from the radio transceiver module.
And in the radio transceiver module which I can talk to which is a plus here there is a code for missing communication with the body control module.
Okay, if you look at the details of each of these codes again, they kind of lead you in the direction of looking at the LIN bus rather than the other networks.
Right, because if we have a U code, well you know what module, what network are we referring to here.
In this case it's that dedicated communication LIN bus between the two modules.
That's where I'm looking.
The other thing I saw once I was in there with the scan tool I can go into the radio transceiver module.
I can start hitting buttons on the key, you know lock on lock and I can see that the module is receiving that information.
You can see that there's a response from that module, so it is actually able to pick up that the key is there.
But for some reason or another that information does not seem to be getting to the body control module.
Okay, now, this is where things got a little bit tricky, kind of hung me up here, but that's kind of why I wanted to share it is, explain the details of what I found and help you to be more prepared.
If you run into one of these systems, at least you'll know, have an idea how this is set up.
So I have to decide where I want to start my testing.
Really, I'm zeroed in on this LIN bus between the two modules.
I decided the BCM was the easier place to start here because, although it's kind of buried up under the driver's side of the dash, I can get to this easier than pulling the headliner down.
So that's where I'm going to start.
So I go to the body control module and I find the connector and I tie into the LIN bus right at the body control module and I'm using my Uscope here and what I find on this wire is there's a 12 volt bias here, and when I first plugged into it I didn't really see any activity.
It was just a flat 12 volts.
Maybe it's shorted 12 volts, I don't know.
Let's play around with the car here and see.
Can we get some communication on this wire?
What I ended up finding out was when you press the start button on the dash, you would actually see some communication happen on this LIN bus coming right out of the BCM.
So it would appear to me that something is happening, and I can't be 100% sure, but it seems as though the body control module is reaching out on the LIN bus at this point, but maybe not.
Maybe it's the radio transceiver module sending some info.
I don't know what it says, but I see information on this LIN bus here when I press the start button.
Okay, so it appears to be intact, but is it making it all the way up to the radio transceiver module?
I don't know.
I did find this, though, when I pressed a button on the key like a lock unlock.
I didn't see any activity on this circuit, which would lead me to believe that either the radio transceiver module is not sending a message out, or it is, and it's just not getting to that side of the circuit at the BCM.
So at this point I pretty much have to go to the radio transceiver module above the headliner.
So I talked to the shop about this because, honestly, I don't want to risk creasing this thing.
Not that I couldn't pull the headliner down enough to get to this thing, but I told them hey, I got to get up there, I'll let you guys handle that.
I don't want to buy a headliner or install a headliner.
That doesn't sound like any fun.
So they get this down enough for me to get to it.
And it is not an easy thing to get to because they couldn't fully or they well, I said they couldn't they didn't fully pull the headliner down, which I don't blame them, it's a lot of work.
They got it down enough so you could get your hand up there and, of course, the connectors on the inner portion of the module.
But I was able to get it, get to the connector and what I did was I unplugged it, brought it over to where I was, got a back probe where I needed or wanted it to be, and then I'd plug it back in so that I could do some testing on this thing and it's not easy to get to, but you can get your hand around there and you can get to the connector.
So again, I'm really interested in the limb bus on this and I want to see what's going on.
So I tie into the limb bus right at the radio transceiver module and at first I did the same thing as before I hit the start button on the dash.
Now when I do this I actually do see some activity on the circuit.
Now I'm using my Uscope and there was no way for me to tell in the moment whether the activity on the network was the same activity that I was seeing down at the BCM.
But I did see some talking going on when I was measuring the Linn bus at the BCM and I see some data packets.
I'm talking going on at the Radio Transceiver module as well.
So to me in the moment it looks like okay circuits intact on both ends.
But the other thing I did was hitting buttons on the key itself and I mentioned down at the BCM and I had to go back to confirm this because it was a little bit of learning as I went to see how the network was reacting to different things happening on the car, but when I would hit the button on the key to unlock or lock, I did see activity at the Radio Transceiver module.
I did not see that same activity.
I didn't see any activity at the BCM, but I did for the start button.
So I'm trying to put the all this together here.
Of course, the thing in my mind is well, maybe there's an open, but I was just trying to see.
You know, are things happening on both ends?
And it seems like, at least for the key function for lock on lock.
I don't see that at the BCM, but I do have my 12 volt bias and data activity on both sides.
And my question is is there one module outputting the bias or do both modules output the bias?
I don't know that and that that's not in a service information that I could find either.
So the easiest thing to do here and this is what I did is just jump the wire from one end to another, right, if there's any possibility that there is an open here, which I think there might be, based on what I'm seeing and what I'm experiencing and the codes that are present.
Just jump the wire from one end to another, and so I do that.
I jump the LIN bus at the BCM all the way up to the radio transceiver and as soon as I do that the vehicle powers up.
Normally when you hit the key, the RF functions work when you hit the lock and unlock and the activity on that network is there on both sides, meaning when I hit the start button I get activity and actually get a little bit more activity than I had before, because what's happening is the BCM is sending a signal out to the radio transceiver and it's actually getting data back about the key, but there's also activity on the LIN bus from the radio
transceiver when I hit the lock and the unlock buttons on the key and that's all there on both sides.
I'll jump them.
Of course it is, but everything works.
So I know for sure I get an open on this wire.
So I looked at the diagram and you wanna look at the factor diagram on this one to see what you need as far as circuitry or connections.
And my issue here was that the LIN bus runs from the radio transceiver control module to a connector that is behind the BCM, and this actually took me a little while because I wanna try to find this open for him.
And if you could picture in your head, the BCM is left front, just ahead of where the left front kick panel is up under the dash.
It's the fuse panel up under the driver's side of the dash, and the radio transceiver module is above the headliner, above where the driver's rear passenger would be, and so the modules are maybe four feet from each other and one would think that the harness would just run along the driver's side of the headliner, come down the driver's side A pillar and then the BCM's right there and there's a harness that goes that way.
But it wasn't quite that easy because I did that visual inspection.
I kind of followed the harness underneath the headliner, down the A-pillar and then it goes into the dash.
There I didn't see anything, but I looked.
There's two different connectors between those two modules.
As far as the LIN bus is concerned, there's one connector that's up behind the dash on the driver's side.
It's actually behind the BCM, not plugged into the BCM but behind it.
And then it goes through another connector which I had to search for the location which is underneath the center console of the vehicle, and then it loops back all the way around back to the BCM where I was measuring it.
So unfortunately this circuit is not going to be as easy as just a quick visual inspection, and the fact that it loops all the way through the center console to a connector and then back around up under the dash back to the BCM, means we got a lot of wire to cover as far as finding an open.
So when I reach a point like this with a shop because I'm not going to start tearing the vehicle apart for a number of reasons, right, I don't want to risk damaging anything.
You know it's just not.
Part of what I do is the repair side of things, so I try to do this little of that as possible.
Also, it is time consuming and I don't really have that built into my day here.
I would obviously charge more if they wanted me to do that, but I usually just kind of put it in the ball back in the shop's court at this point and most of the time everybody's okay with that.
They just want some direction.
What am I looking for?
What's broken?
Why is this?
You know acting the way it is and I can say, hey, you're open wire somewhere within here.
You guys just have to tear it apart and see what you can find and also giving them the option of, if they want to overlay it, they can do that right, meaning they just run a new wire and not worry about finding the broken wire.
Now, of course, you know, when I was a tech, I wanted to find the broken wire because my thought process is there's probably going to be more than one broken wire.
Right, if the harness is rubbing on something or it's pinched or something like that, you know there could be more damage yet to come for other circuits that hasn't presented itself yet, and if you just overlay the wire, well, you could have more issues later.
Again, I like putting that in the shop's court and let them make that decision for them and their customer.
Right, my job is to tell them what's wrong and I'll get them as close as they can and then let them decide.
And what they decided to do is overlay a wire.
Fine, I don't care, it'll work.
It's just whether there'll be more issues in the future from wherever that wire is actually broken.
So I didn't get to find out exactly where this Linn bus wire was broken, but jumping it from one side to another fixed all the issues that they were having and it brought the key information to the body control module from the radio transceiver, which is what we needed.
So that's all I've got for this one today.
Hopefully that was interesting.
Hopefully it helps you out if you're dealing with any of these proximity key system issues.
They're not too terribly complicated If you take the time to understand them.
You have some testing equipment and then you understand the basic systems.
But also, I mean, this is a 2020.
It's pretty new car.
It's working the same as stuff that we saw 10 years prior to.
So we can make this stuff happen.
We can figure out what's wrong.
It's not too big of an issue.
But with that all the way, I just want to thank everybody for listening.
Let's get out there.
Starfix in the world, one car at a time.
It is called Star MX's car, overattered to treadmill.
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