Sometimes a car’s computer module fails and the new one is too expensive or hard to find. People buy a used one, but the car usually needs it to be set up so it works correctly.
Programming is how you “set up” a used car computer so it matches your specific vehicle. Without it, the module may not communicate or may not work properly.
SJ Auto Solutions is mentioned as a company that helps with used car computer modules. If you’re stuck finding or setting up a replacement, they’re presented as a place to get help.
Tommy Oliva is mentioned as the person offering cloning and support for used car computer modules. The idea is to help you get the replacement working correctly.
Bench testing means checking the car’s computer on a workbench instead of in the car. It helps you confirm it’s actually working before you waste time or money installing it.
When a mechanic says a module is “bad,” they mean it’s the part that’s actually broken. The goal is to prove it’s the module, not a wiring problem or a sensor problem, before replacing it.
They reconnect the car’s wiring a little at a time to see which connection makes the problem come back. When the problem returns, you’ve found the likely culprit circuit.
They remove connectors one by one to see which connection is causing the battery drain or wake-up. The goal is to find the specific part of the wiring that triggers the issue.
Cornering lights are the lights that help illuminate the road when you turn. If an aftermarket replacement doesn’t match the original electrical behavior, the car may detect a “bulb out” condition and cause other issues.
This means guessing and replacing parts without testing first. It can waste money and time, especially if the expensive part isn’t actually the problem.
Modern cars have lots of computers that work together. On a bench you may not have all the other signals the module expects, so you have to recreate them to test properly.
They’re a company the host recommends for a bench testing harness. The important part is that the harness makes it easier to connect power, ground, and data wires to a module on your workbench.
On the CAN data network, resistors help the signal stay clean and stable. If you’re testing on a bench, you may need termination so the data communication works properly.
Go Diag is another device people use to break out the OBD2 connections for bench testing. The host says its built-in lights (LEDs) might interfere with programming, so it may not be ideal if you’re trying to reflash modules.
A pinout is the map of which connector pins correspond to functions like power, ground, and communication lines. For bench testing, the pinout is critical because misidentifying pins can prevent communication or damage the module.
“Body network” refers to the vehicle’s communication segment that connects body-related modules (comfort, lighting, etc.). The host notes that wake-up requirements for bench communication are often tied to this network behavior.
Drivability diagnostics means figuring out why the car doesn’t run smoothly—like stalling, hesitation, or rough running. It uses scan tool data and electrical tests to find the problem.
Electrical diagnostics means checking the car’s wiring and electrical signals to find faults. It helps confirm the module is getting power and communicating correctly.
A test light is a basic tool that checks whether electricity is present on a wire. In this episode, they’re using it in a clever way to try to wake the module up.
A “12 volt feed” is a dedicated switched or constant 12V power supply used to power or wake certain modules. The speaker suggests modules with a dedicated ignition/wake 12V input are more likely to communicate on the bench.
Chrysler is mentioned as an example of how some cars route messages through a gateway. Even then, you can often still communicate on the main high-speed network.
Medium-speed CAN is a slower car communication network than the high-speed one. Some modules on it may not be as directly reachable from your scan tool.
Body CAN refers to the CAN network used for body-related functions (comfort, lighting, convenience modules, etc.). In diagnostics, it can be harder to access directly from the scan tool depending on gateways and routing.
This is a power supply you use on your workbench. It lets you set the voltage and watch how much current the module uses, so you can tell if it’s alive before you troubleshoot further.
When a module is powered but not doing anything, it usually still uses a small amount of current. If it uses almost none (or none at all), it may be dead or not wired correctly.
CAN bus is the car’s internal communication system between computers. On a bench, you have to set up the network correctly so the module can “hear” and “talk” like it would in the car.
A bench harness is a wiring setup that lets you test a car module outside the car. It provides the right connections—like power and network wires—so your tools can communicate with it.
A breakout box is a connector interface that makes it easier to reach the module’s pins. It helps you plug in tools and add things like a resistor without messy wiring.
A “completely dead module” is a module that shows no meaningful power-up behavior—often reflected by near-zero current draw and lack of communication. Distinguishing this from a module that powers up but fails specific functions is a key diagnostic step.
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Welcome to the Automotive Diagnostic Podcast.
We're going to explore ways to sharpen our diagnostic skills, find learning resources,
and hear from experts in the automotive field.
Hey have you ever been faced with the challenge of sourcing, installing, and programming a
used control module in a vehicle? I know a lot of us have. It seems to be happening more and
more often today with the volume of control modules on vehicles, the cost of some new ones,
or even the availability of new control modules. In some cases used may be the only option. So
what do you do here? I strongly recommend checking out SJ Auto Solutions and Tommy Oliva.
Tommy offers a cloning service for used control modules to make these things plug and play for
the vehicle that you're working on. In a lot of cases he is also able to source the control
modules if you're unable to locate one for the vehicle that you're working on. But once you get
connected with Tommy, he's going to offer fantastic support from start to finish to make sure that
that control module is going to work in your application. He's also got tech support that he
offers through his website, along with some free resources there as well on information about used
control module programming. So make sure to check out SJ Auto Solutions. I can't recommend that enough.
Hey, what's going on automotive world? Welcome to another episode of the automotive
diagnostic podcast. My name is Sean Tipping. I'll be host once again for this week's episode. Thank you
so much for joining me. Just me on the show this week. And what I'm going to be talking about this
week is bench testing control modules that is connecting to the module on the bench away from
the car, how to do it, why it's useful, and where it has saved me from making a bad call or at least
pointing me in the right direction so I can make the correct call. So I do this frequently throughout
the mobile diagnostics module programming module cloning. And honestly, the module cloning and
programming part of this is where I sort of develop the skill to be able to connect to a
module on the bench, communicate with it and maybe even run certain functions. But really the
powering a module up and getting it to turn on getting it to communicate and then again maybe do
something that actually becomes helpful to know how to do if you're going to get to the point of
actually condemning a control module or deciding the problems on the car, right? It splits the
direction that you're going to go. It eliminates half of the problem so that you can go after
the right thing. And sometimes we need that. Sometimes that actually is really helpful.
And where this comes from is I was doing a class this last week for a group in Australia,
a webinar, and it's called how to condemn a control module. And I've presented that class
a few times, but it goes through exactly that. Like what are all the steps in order to successfully
say the problems in the module needs to be replaced or the problem is on the car, right?
Circuits, input, output, communication networks, power, ground, wake up, whatever, right? What is
the problem on the car or know the modules fail that needs to be replaced. So that's where this
comes from. And it is part of my test procedure in some cases. Now, you don't always need to do this.
Sometimes it's very clear and very simple that, hey, I have everything for this module to operate.
It is not operating. It needs to be replaced. Okay, sometimes there's visible damage to the module,
which you're still taking it out maybe and taking it out of the case. But you don't need to bench
test it in that case. But modules are complex. They're nuanced. There's lots of variation to the
modules, to the circuits, to the problems that they can have. And sometimes it is more difficult to say
that, hey, this module is not doing the thing it's supposed to do. And it's definitely the module.
Or it could be an individual circuit on the car that is causing it or something else on the car
that is causing this to happen. And one example that pops up in my head is there was a Cadillac
that I did a case study on the show on a few years back. It was a parasitic draw. BCM was waking up
and talking on the low speed bus. And it was very difficult to say that it was either the BCM or it
was a circuit. And what I ended up doing was kind of separating the BCM from the car in a way. And
then adding circuits in one at a time until, oh, okay, this caused the BCM to wake up when I add in
this circuit. And that one I kind of did by connector. So I would unplug one connector at a time. So
there's variations of this that you could take. But had I fully removed that control module,
powered it up on the bench, which is kind of what I did, it would not have woke up,
it would not have talked on the low speed bus. But there was a circuit that went to one of the
cornering light assemblies that had been replaced with an aftermarket unit. And the bulb outage
circuit was pulling a bias voltage down to ground periodically. And that was waking up the bus on
this one. And that was tough to find. That was, you know, going circuit by circuit. But in a case
like that, being able to at least eliminate the control module as the source of the problem is
actually kind of big, right? Now, yeah, you could chuck a part at it. But we all know sometimes
these modules are hard to get. Maybe they're expensive. You don't want to be spending the
customer's money on something that doesn't need because just to try a module, you know,
you've got a program and set it up to the car. So we want to make the right call before we're
chucking parts at the thing. And if nothing else, this gives you some confidence as well
to say like, Hey, I've got it out of the car. And I see the same problem that I expected, right,
that this module is failed. It's also failed on the bench. Okay, so it's not something to do with
the car. Or, you know, this module wakes up and talks when it's not supposed to build us that on
the bench, right? And there's a lot of different problems that you can identify. Some are going
to be tough to do on the bench, right? Obviously, modules exist on a network in most cases,
they rely on a lot of other circuits to actually run the functions that they need to,
some of these functions are going to be difficult to mimic on a bench, not impossible,
you can get creative and you can be the input, you can be the output in a lot of cases. But
this is a useful test method. And here's the thing, if you actually take the time to do this,
and maybe you do module programming cloning bench work already, and you might be familiar
with hooking up to a module on the bench. But if you're not doing this, actually going through it
and connecting to a module on a bench will help your diagnostic skills when you are in the car,
right? So when you're actually doing the diagnostic in the car, you're like, what does
this module need to function? You're going to be better at that if you've taken the time to actually
set up a module on the bench and talk to it that way. So I found it has actually increased
my diagnostic skills, even if I'm not using the method on every single car. Okay, so we've got
the module out on the bench. And this is kind of the bulk of the episode here, I just want to give
you some tips and some advice as far as getting set up, what tools you're going to need, and what
obstacles you might run up against. Okay, so number one, you're going to need something
to connect to the module. And then in most cases, you're going to be connecting your scan tool to
the module and talking to it directly on the bench. Now, there are some obstacles, there are
some hurdles, but what you're going to want to get is some sort of bench test harness. Now,
I'll put a link in the show notes, auto rescue tools has a really simple but effective bench
harness. It is literally just a OBD2 plug. And then it has a bunch of wires going off of it with
pins at the end, female pins of various sizes that link to the pins on the OBD2 port, right? So
power ground communication, you know, pin one, you know, there's single line communication,
there's can communication, you have all 16 pins, okay, and they're going to be connected to these
wires with various pin sizes. There's also some switches to turn on and off power. And then there
is a female plug that you can plug in a power source and some banana jacks. So you can plug in
power sources that way or add on leads to it if you need to. So it's very versatile, you can connect
to most modules using just this bench harness comes with a couple terminating resistors,
we'll touch on that. But it's the most effective and very reasonable cost. And we have one of these
in the shop, we have one in every van. You can use it for module programming as well, like you want
to do the actual module programming on the bench with whatever programming software you have. Now,
those often will have their own harness to connect to it, but you could use this as well.
But there's nothing in between the OBD2 port and the actual connections on the module. There is some
other breakout boxes like the Go Diag that you can use, but I've been told by people that the LEDs
that are in the actual like breakout box portion of the Go Diag can affect programming. So if you
just want to talk to something on the bench, I think it's an effective tool. But I'd be more
careful about programming something on the bench using the Go Diag. Anyways, a couple different
tools there, I'll put the link in the show notes to the auto rescue one. Now, you're going to need
a diagram and a pinout in order to find the connections to the module you need. Now, of course,
there's going to be power, there's going to be ground, most likely communication of some sort.
And then there's also going to be a wake up in some cases, like an ignition wake up of some sort.
Now, this does get a little tricky sometimes, you know, sometimes it's a separate circuit
that is just, you know, ignition wake up, it's a switched feed, and you'll have to find that on
your diagram. Sometimes that happens through the communication lines themselves. And
if this is the case where the module needs a message from another module in order to wake up
and start talking, this is probably the biggest hurdle to actually communicating with a module
on a bench. I'll give you some ways you might be able to get around this. But this is a situation
where there's a possibility you may not just you may not be able to communicate with it on a bench,
if it needs a specific wake up message. And typically what I have found this is over like
body network of some sort. But you'll see these, we're looking at the diagram for the module,
it's got a constant power, a constant ground, and then like two can lines, and that's it,
as far as like being woken up, there's no individual ignition feed. Now there are some modules where
if you boot them up, and then you try to talk to it immediately with the scan tool,
it will communicate. And sometimes you have to be a little creative with that and catch it.
Because a lot of these modules, even if they are meant to receive a specific wake up on the can,
if you first boot them up, right, you just give it power and ground, it'll wake up and be like,
hey, who's there, I just woke up, and then it'll quickly go back to sleep and not talk until it
gets the correct message. So that can definitely happen. But what I like to do is in a situation
like that is I will take my scope, and I will actually put it onto the network pins, whatever
that form takes for that module, and then I will remove and connect power ground to boot the thing
up. And I'll watch and see does this thing shoot out a few messages onto the can network or not.
And if it does, this episode is brought to you by L one automotive training and Keith Perkins.
If you're looking for education on module programming, J 25 34, E Prom work, key in a
mobilizer, electrical diagnostics or drivability diagnostics, Keith has a website L one training
dot com that's got over 60 hours of training videos on all those subjects and more. When I
first started out doing mobile, I utilized Keith videos on module programming and J 25 34,
in order to get my head wrapped around what I would need for the tooling, the computers,
the software setups, you know, what kind of obstacles I would be up against when I'm out
there programming modules on cars. And it was a huge benefit to me. And I continue to use the
training videos that he has on his website. So I strongly recommend checking out L one training
calm. The link is in the show notes. What I'll do is I'll try to catch it and you have to time it
right. But you're doing the connect to module and your scan tool, like right as you're booting
that thing up. And sometimes you can catch it and then a lot of times once you maintain or like
begin that communication, it will maintain will stay awake and continue talking. So again, that's
hurdle. But you can look at to see if is there anything, you know, coming out of the
network lines once I boot this up. The other things you can do here, actually, on that note,
the other thing I found works on some not all is if you take a powered up test light and you
touch it to the network pins on the module, it may actually wake up and start talking from that
to because it sees at least something on that boss and it's like, Hey, somebody's talking
what's going on. And you can catch it that way. Again, doesn't work for everything. There are
modules I found that just won't talk on the bench. You have to have them in the car. You have to have
that wake up signal, you know, from that module, whoever's the power mode master in the vehicle
needs to be on that network as well. So there is a limitation there that I want to point out.
But lots and lots and lots of modules you can talk, especially the ones that use a dedicated
ignition, wake up like 12 volt feed. If you've got that, you're probably going to be able to
talk to this on the bench. Okay, now, you also want to pay attention to what network does that
module talk to or talk on normally? And how does that link up to the OBD two port in the car,
right? Because your scan tool is going to be connected to the OBD two port in the car. And
as far as it's where on the bench, it's still connected to the OBD two port on the car. So
the module you are trying to talk to, does it exist on the network that goes to the OBD two port?
Is there a gateway? Is there some sort of, you know, restriction between the scan tool and
the module that you're trying to talk to? Does that module normally talk to the scan tool? Of
course, that would be an obvious question to ask. But there are modules that are on proprietary
can networks that don't directly talk to your scan tool, you get the information through
another module. Or maybe it's just, you know, it is a network, but it does not normally connect
to the scan tool, it gets translated through another module that's on that network. What I
have found is if it's connected directly to the OBD two port, you're going to use your diagram and
figure out, okay, well, what pin do I need to connect to the network wire, and then connect it
up that way. But if it's a high speed can, it will usually work. Even if you have a gateway
module. So Chrysler, for instance, if you have an actual secure gateway module, your scan tool is
talking to that and then it's translating messages from the modules. But you can go straight onto
the high speed can and talk to it. It's the same protocol. Now there are medium speed cans and
body cans, and you may run into limitations there as well. So the actual communication with
the scan tool, there could be an obstacle. But that's what you want to take a look at is the
diagram. How does this module normally communicate with the scan tool? What is the pathway? And
how am I going to connect to it? Now, beyond that, like I said, you can scope and just see
is there traffic coming out of whatever network line is on that module. And that's a really good
sign that hey, that module is waking up and talking. Another really simple thing that you can do that
you probably should be doing if you're doing this method is looking at the amperage the module is
taking. Now you can do this either through the power source that you're using, if it has a
measurement for amperage, which a lot of them do. And I'd recommend just get a stable, you know,
bench top power source, if you're going to be doing any bench work with modules, because it's
nice to be able to dial the voltage and again, read the amperage that the module is taking.
But you can just use a little inductive amp clamp. If you're using the go diag,
it has an ammeter built in so you can see. But this tells you a couple things. You know,
is the module turning on at all, right? Now, if you have the wrong connections, right,
you put those wires in the incorrect spot on the module. Well, number one, you could potentially
cause some damage to do pay attention to the pinout as you're connecting these to the module.
But this can kind of prove if you've got them in the right spot that this module really is dead,
it is not waking up at all, right? There's no current draw from this thing. That's a bad sign
for a module when you first hook up power and ground. Usually what I see modules are going to
be somewhere in the like two to 400 milliamp range when they're just on, not running any functions
or anything like that. But just on, they're awake. They're ready to do something. They're
going to communicate, you know, that 300 milliamps is like the probably the most common that I see
for most modules. There'll be ones that are outside of that range. I'm sure. But if you hook
it up and there's zero, there's nothing. It's not drawing any current or, you know, it's just
a few milliamps. That's a bad sign for that module. That again, connections, correct.
That is pointing to there is something wrong with this module. And that's where I'll double
check my pinout. I'll double check my wiring diagram. Am I missing a wake up? Am I missing a
power feed or a ground or something that this module needs to actually wake up and communicate?
But that can tell you something that can point to if that module is failed or not. Now, if you do
get this thing awake and you want to talk to with your scan tool, when you're in the scan tool,
do be aware that again, your scan tool is normally going to talk to the whole vehicle.
And it's going to get its VIN number from a particular module that could be a BCM or a PCM
depends on the car. But it might not be the module you're trying to connect to. So you may have to
manually build that vehicle within your scan tool, meaning that you are setting up the vehicle
yourself and getting to that topology screen and then picking the module specifically that you
want to talk to this most likely will not be the same path that you take when you just do an auto
scan. Again, maybe it's the module that the car normally gets the VIN from. Okay, but a lot of
times what I do on the bench is manually building the vehicle and then manually selecting the module.
One other note on the can bus side of things, if you're connecting to a module and it's using can
bus, you are going to need to know if that module contains a terminating resistor or not. And in
my experience, modules that do contain a terminating resistor within them, you know, ECM is very
common to have a terminating resistor. If it has one, you generally don't have to add one on the
bench. But if that module talks on can, and it has no terminating resistor, you are most likely
going to have to add one. So how would you do that bench harness that I mentioned, you'll have two
extra pins, because there's a two can high to candle and the pin the female pins are different
sizes. So you can connect to different modules. So you take the two that you're not using, and you
put a 120 ohm resistor across there. And most of these kits will come with resistors in them. I
think the go diag does and I know the auto rescue one does. So you have them right there and you
just are going to connect those with the go diag, you could use the actual ports on the breakout
box itself and just connect up a resistor, you can even make your own with, you know,
nano jack ends and connect it up that way, however you want. But adding that terminating
resistor may be necessary for scan tool communication. And again, this is where I'll
have my scope out. Like if things just aren't working, I can't talk to it. I'll use my uScope,
and I will look to see what is happening on the circuits where I'm expecting
network activity. What does it look like? And you can tell if a network, a can network has no
terminating resistance, it's like this repeating ringing pattern where it kind of ramps up,
drops off, ramps up, drops off, happens really fast and just keeps repeating itself over and
over again. Doesn't look like a regular like square wave can wave form that you would expect to see.
But you add in that 120 and then it looks great. And you don't need the full 60 in my experience,
just one resistor is fine. And then the scan tool is able to communicate. So something to keep in
mind, if you're doing with a single wire network, bear in mind that certain modules are the master
of those networks, and needed to provide like a bias voltage, right? So like, you won't be doing
a lint bus, but something similar to a lint bus, there may need to be, you know, a master of that
network that is present. And there's a potential that your scan tool may provide what's needed
there, but there are situations where it won't. So again, when you get into the single wire network
stuff, you may run into some challenges there as well. But use the scope, see what you got going
on there. And then again, you can always fall back to, you know, scope in the network, but then
looking at the amount of amperage that module is drawing on the bench and saying, oh, and this would
be the case of a completely dead module in the car, right? But if it's turning on, it's doing
something, okay, I have to reconsider, do I need to look at the car? Now, as far as running specific
functions, right, inputs, outputs, things like that, you can look at your diagram, find the pin,
and then see, okay, can I run, you know, that specific function, you know, out of the car?
I don't find myself doing this quite as often with this test, but every once in a while, you know,
I want to make sure, hey, either you can or can't do this particular function. And then I'll set
something up to either simulate an input or simulate an output, and then see if I can run that
function on that module. And it's again, just about finding the pins on the module connecting to it
and simulating something that would be in the car. But that is where I'm going to wrap this one up
today, a little bit shorter. But I think this is a useful test method in certain situations. And
again, at the very least, it will increase your diagnostic capability, when you are trying to
determine in the car, what does this module need to function. So give it a try, if you haven't,
check out the link in the show note, if you need one of those bench harnesses.
And then feel free to shoot me any questions you got on this stuff. And I'll be happy to try and
help out. But with that all out of the way, let's get out there, start fixing the world, one car at a time.
About this episode
Used control modules are increasingly the only practical option, so the host focuses on bench testing as a way to avoid misdiagnosis and wasted parts. After a webinar on “how to condemn a control module,” he explains when bench testing helps—especially when module failure vs. a circuit issue is unclear—using a Cadillac case where a cornering-light aftermarket bulb circuit woke the BCM on the bus. He then walks through bench harness setup, pinouts, wake-up hurdles, scope/amperage checks, scan-tool communication paths, and when to add CAN terminating resistors.
This week on the show I share some tips and tricks on bench testing control modules as a diagnostic method. See the link below for the bench harness mentioned in the show.
