“Downstream effects” refers to how one fault can trigger other symptoms elsewhere in the vehicle. In diagnostics, a single sensor or control-module issue can cascade into multiple drivability, warning-light, or limp-mode behaviors.
This is a big luxury SUV from Cadillac. The host is using the 2016 Escalade to show how a specific computer fault can cause other problems too, not just one simple issue.
That means the Escalade has a big engine with eight cylinders. “6.2 liters” is the engine’s size, and it usually helps the car pull strongly at lower speeds.
An intermittent problem is the kind that doesn’t happen all the time. It can be frustrating because the car may act normal when you check it, so the shop has to wait or test in a more specific way.
ISTA is the BMW dealer/tech tool software that talks to the car’s computer systems. It’s used to diagnose problems and to update or program the car’s modules.
A modem in a car is the part that handles its internet/phone-style connection. If the car needs to download or verify software, that connection can influence the update time.
A programming event is when the car’s computer software is updated or rewritten. It can take a while because the car has to do multiple checks before it’s done.
Limp mode is when the car intentionally reduces power. It usually happens when the computer finds a problem and wants to keep you from driving too hard until it’s fixed.
This phrase means the car’s throttle isn’t behaving the way the computer expects. The throttle plate may not be moving correctly to match the commands the computer is sending.
When the car detects a problem, it may intentionally limit how much power the engine can make. This helps prevent further issues and lets you keep driving.
Aftermarket parts are replacements from other brands. Sometimes they don’t match the original behavior closely enough, so the same warning/problem can come back.
An electric throttle body is the part that controls how open the engine’s air intake is. Instead of a cable, the computer moves it and checks its position.
An H bridge circuit is electronics that let the computer spin a motor forward or backward. For the throttle, it’s how the system can move the throttle both open and closed.
Pulse width modulation is a way computers control power by turning it on and off very quickly. By changing how long it stays “on,” the computer can control the throttle more precisely.
SENT is a type of data link used by some sensors to send readings back to the car’s computer. Here, the throttle uses it to report its position to the ECM.
Enable criteria are the specific conditions the ECM must see before it will evaluate a sensor/actuator behavior and set a diagnostic trouble code. This can include engine running vs. key-on/engine-off states and other prerequisite signals.
Key off refers to the ignition being turned off while the vehicle’s electrical system may still be in a defined state for diagnostics. Some ECM fault logic can still run during key-off conditions if the required signals and criteria are satisfied.
A “two-wire circuit” is a simple electrical connection with only two wires going to a part. When a code points to that circuit, it usually means the problem could be in the wiring or the way power is being sent to that part.
An H-bridge is an electronic circuit that can make a DC motor spin one way or the other. That’s important for throttle actuators because the car needs to move the throttle accurately in both directions.
This is a setting the computer uses to account for how the throttle body affects airflow. If the number is low, it can be a sign the throttle area is dirty and air isn’t flowing the way the computer expects.
The throttle bore is the inside channel in the throttle body where air passes. If it gets dirty with carbon, airflow can change and the car’s computer has to compensate.
Throttle body cleaning means removing gunk from the throttle plate area. If the throttle is dirty, it can stick and cause sensor or control problems.
Term
tack motor parameters
This is about the settings the car uses to control the throttle motor. If those settings aren’t enabled or correct, the computer may not be able to command the throttle properly.
The accelerator pedal tells the car what you want—more or less power. In an electronic throttle system, the computer uses that input to command the throttle.
Circuit testing means checking the electrical signals and wiring. It helps find problems like broken wires, bad connections, or incorrect signals to the throttle motor.
This is pulse-width modulation (PWM), which is how the computer controls the throttle motor without using a steady voltage. It turns power on and off very fast to get the right movement and holding force.
Term
sense protocol data line
A “sense protocol data line” is a dedicated communication path used by the throttle control system to send information to the ECM. The host notes it’s a one-way communication link, which affects what you can and can’t conclude when diagnosing a throttle fault.
A scan tool is the diagnostic device used to read trouble codes and live data from the ECM. Here, the host watches the scan tool while trying to reproduce the fault to see whether the commanded throttle behavior matches what the ECM expects.
This means you turn the ignition on, but don’t start the engine. The car still powers up its computers and runs checks, so it’s a good time to diagnose problems safely in the shop.
An amp clamp measures how much electrical current is flowing in a wire. By measuring the throttle’s wire current while you command the throttle, you can tell if the throttle is drawing the expected amount of power.
The engine control module is the car’s main computer for the engine. It controls things like throttle behavior and also talks to other systems over the car’s network.
Throttle codes are error codes the car stores when there’s a problem with the electronic throttle. They help point you toward what part of the throttle system isn’t behaving correctly.
CAN bus is the car’s communication network. It’s how the different computers in the car talk to each other, and in this case the signals get messed up when the throttle is commanded.
Ground feeds are the wires that connect a car computer to the car’s electrical ground. If that ground is bad, the computer can behave erratically and even mess up communication with other modules.
Case grounded means the ECM’s ground connection is made through the metal housing. That lets you test grounding by attaching to the ECM case instead of only at the connector pins.
The throttle motor is the part that actually moves the throttle valve. The car’s computer tells it what to do, and the diagnosis checks whether the wiring to it is shorted or not.
The throttle circuit is the wiring and control path that powers and commands the throttle motor. If it’s shorted, the car can pull too much current and the throttle may behave incorrectly.
Ohm checking means measuring resistance with a meter to see if the wiring is healthy. It helps confirm whether there’s a short or an open connection in the throttle circuit.
A short to ground means the wire is accidentally touching the car’s ground. That can cause too much current to flow when the computer tries to control the throttle.
The driver circuit is the part of the ECM that powers the throttle motor. If there’s a short in the throttle wiring, the driver circuit can draw too much current and cause wider electrical problems.
CAN low is the other wire in the car’s communication network. Looking at CAN low with CAN high helps confirm whether the network signals are being disrupted.
CAN high is one wire in the car’s communication network. Checking it (along with CAN low) helps you see whether the network signals look normal or messed up.
The fuel rail is the metal part that holds and distributes pressurized fuel to the injectors. If a wire gets damaged and touches it, it can short and cause major electrical problems.
The upper intake manifold is part of the engine’s air path. If the wiring harness isn’t secured there, it can rub from movement and eventually expose a wire.
“Shorted to ground” means the wire accidentally touches the car’s ground. That can make the circuit draw too much current and cause other systems to act up.
This is the wiring that controls the fuel injectors—how the car delivers fuel. They’re using it as a comparison to see whether a similar wiring short would affect the car’s communication network the same way.
This circuit controls how the car regulates fuel pressure. They’re asking whether a wiring short there would cause the same kind of communication/network problems as the throttle circuit did.
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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.
This show is brought to you by Automotive Seminars. If you're looking to stay up on the cutting-edge
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and a ton more. Once you purchase one of these training seminars, you can access this at any
time that you want through your account at automotiveseminars.com. You can re-watch the
training a year, two years later, which makes this training even more valuable. I highly
recommend you check this out. The link is in the show notes. Hey, what's going on? Automotive
World, welcome to another episode of the Automotive Diagnostic Podcast. My name is Sean Tipping.
I'll be your host once again for this week's episode. Thank you so much for joining me.
This week on the show, I've got another case study for you. This is from out in the real world
doing mobile diagnostics at repair shops. Well, and I guess our repair shop as well,
but that's where most of my case studies are coming from is getting called out to repair shops
that either don't have the time to or don't want to deal with the challenges that we run into on
some of these vehicles, this definitely being one of them. And it was pretty interesting,
not so much the problem or the actual thing that was wrong with the car, but the downstream symptoms
that it caused. And you'll understand what I mean when I get there, but that's the case a lot of
the time when we get into or you get to the root cause of what's wrong with the car. Like you
finally find the thing that is broken that you need to fix and you're like, well, this isn't
really exciting. This isn't anything new. This is something I've seen before or anybody could fix,
but the symptoms that it causes in the way that it presents itself ends up being very interesting
or the way the downstream effects of the problem end up being very interesting. So that's this one.
Anyways, I'll give you the setup here. This is a 2016 Cadillac Escalade with a 6.2 liter V8.
Okay. And this was that one of our repair shops, which quite frankly,
doing in-depth diagnostics for this particular shop is difficult because they have a very small
shop and a very high volume of cars that they work on. Some of these cars are questionable as
far as should they be on the road or not. And this time of year, it kind of gets tough too,
because it is really hot here. Hit 100 degrees Fahrenheit here last week and it's gross to
be working outside. So if it's not something straightforward and simple, we either tell them,
hey, you got to get this inside or we have the nice option now of saying, hey, bring it to our
shop. And our shop's small. We fit about four cars in there, few in the parking lot, but we
will often bring things that we recognize either A as a problem and we know it's going to be a
problem in depth. Maybe we have to research, experiment. It's not going to be a
straightforward matter. Hey, just get it to our shop. We'll deal with it. If it's intermittent,
again, we try to avoid those if we can, but sometimes we get involved. Sometimes we want to
solve it. Bring it to our shop. We'll keep it for a period of time. We'll figure it out there.
Like BMW programming where we're using ISTA and we're connected directly to the modem,
even still the programming will take two to four hours depending on the car and what's needed,
which I don't get, by the way, maybe somebody can explain it to me why we're going to the
trouble of hardwiring to our internet modem. And yet the programming events takes like eight times
as long as any other manufacturer, I guess I shouldn't say that. There's examples where we
did a Ford the other day that took, oh, it was two or three hours on a telematics module. So
that stuff is popping up more and more. Anyways, that's the sidetrack. We bring cars to the shop
for certain things and it's nice to have that option. And it's a nice easy out to if like,
hey, this car is going to be a problem for whatever reason. We'll just say, hey,
this is not the optimal situation for us to do this in either, you know, set it up for us the
way that we would like, or, you know, you can bring it over to our shop and then we'll handle it
there. And it's a little bit more of a controlled environment. So we ended up doing it that on
this particular car. Now, we did have a couple of visits to this, the shop that we go to,
they are high volume, like I mentioned, we'll usually go out there and look at two or three cars
at a time, if not more, which is nice as a mobile company, if you're going to start a
mobile business, drive time is your biggest like efficiency killer going from shop to shop.
As a tech, it's nice to break up the day. But as a business, it is an absolute killer because
you're making $0 for all employees during that drive time. How can you reduce drive time? Now,
obviously, you can do scheduling and look at your, you know, geographical setup on,
you know, appointment to appointment and all that stuff. But the best way to do it is to have
multiple cars at one stop, because you eliminate a 20, 30 minute drive in between those two vehicles.
So we like doing work for the shop. And we go there often. Now, we had been there a few times
for other vehicles. And we had looked at this one a couple times, one of my technicians did.
And again, just to recap, 2016 Calac Escalade with 6.2 liter, and it's going into limp mode.
You need reduced power, check engine light on, you can't accelerate, the engine will still run.
And this is happening, happening fairly enough that it's a problem for the customer. It's not
every single time that you start up and drive it. But enough that they have decided they
are not going to continue to drive this, they need to get it fixed. Okay, it's in at
the shop. And the code that is setting is a P2101, which essentially just says throttle actuator
position performance. That's pretty much it for this particular code. And if you look at the
details, it says the ECM detects the actual throttle position does not match the predicted
throttle position for greater than one second, or the ECM detects the throttle is driving or the
throttle control is driving the throttle in the incorrect direction or exceed the reduced power
limit. Okay, and that's there's more to the code as far as like, enable criteria and stuff like that
for testing. But those are the two conditions that will set this 2101 in the engine control module,
that the throttle position doesn't match its predicted position position that the ECM wants it
at, or that it's driving it in the wrong direction, or exceeded, or exceed the reduced power limit.
So meaning that, hey, we've limited the power output for this engine, but the throttle is
past that. So that's how you would get this particular code to set or those are the conditions
that would set this particular code. So this code is happening fairly often on this thing it would
set. And we got it to happen every once in a while. And they had already replaced a couple throttle
motors on this one. And when my guy was there, he's having some challenges getting this to actually
act up consistently. And he was looking at the data stream, he was looking at stuff and didn't
really get a conclusive answer on it because it was kind of intermittent. And he basically told
him, hey, love to spend some more time on this. But where did you get the throttle body from?
Because he said he already replaced the throttle body on this thing. And it's still happening.
But the problem that we run into quite often, I mean, with a number of parts, but electric
throttle bodies being one of them, is an aftermarket throttle body could present the same
different problems than the one that you had in there. And we don't even know,
was this the original code? It's the original problem. Was it the original code? We don't know.
We've seen aftermarket throttle bodies. And we said, hey, we don't have time to get to the bottom
of this. But one thing you should consider if you need to get this fixed fast is look at the
component that you put in and maybe get a high quality part. They said, okay, we'll take a look
at it. And when you guys can get more into it, we will. They ended up putting like an OE throttle
body on this thing, didn't fix it. We didn't have time to get back to it. They are really
chomping at the bit or the owner of the vehicles chomping at the bit to get this thing fixed back
on the road. And so they ended up getting a used engine control module for it. And then they said,
hey, I realize you guys don't have time to get to the bottom of this problem right now. But can
you come clone an ECM for us? Sure, we can do that. That's pretty straightforward. I can,
you know, block off a half hour of time in order to do that. It's predictable. I like
programming for that reason. It's much more predictable as the amount of time that you're
going to spend. So we do that, we program the engine control module, which is used, but it was
the correct part and cloned it over to the vehicle and got a program. And they ended up
having the same problem and the same code. So at this time, they're like, hey, we've done the
throttle body a couple different times. Actually, I think it ended up being three times total.
And we've replaced the engine control module, but we're still having the same issue. And then
that's why I said, just you need to get this one up to our shop here, because we just we don't
have time to sit out in the scorching heat to try to nail down this intermittent problem,
like bring it to our shop, it's air conditioned, we'll take care of it there. So they do, they
get it up there last week for us. And my guys at the shop were kind of messing around with it.
And we got a little bit more of like what the problem actually was, granted, yes, still intermittent,
but we can consistently set this P 2101 code. And that's what we were for sure after. And
at this point, this is when I got actually like personally involved with the vehicle. So then I
started researching the code a little bit to see, okay, what's the criteria for this code to set.
And I know I'm going to be going in and looking at the electric throttle body operation.
It's a pretty straightforward system, right? It's two wires, H bridge, H bridge circuit in the ECM,
it can move the throttle either direction, you know, pulse width modulated in either direction.
And it has a sensor unit to tell the position. And the sensor unit on this one actually uses
a sent communication line. So it's like, it's a little module almost sending data on a data line
or communication line between the throttle body and the ECM on this and General Motors been using
that for quite a bit of time. But really, it's just there are precision sensors built in to
the throttle body itself, because of course, we want to know what position is actually at.
And then we've got the two control wires. So my goal is if I have a code that's related to anything,
but in this case, the electric throttle, I want to understand what portion of this is it actually
looking at to determine failure or not. Okay, and again, I mentioned the code definition where it
says the ECM detects the actual trial position does not match predicted throttle position for
greater than one second. So I could assume that okay, the throttle is not where it wants it to be.
The second part again, detects the throttle controls driving the throttle in the incorrect
direction or exceeded the reduced power limit. I don't have 100% clarity on exactly what that
means. But again, throttle moving in the wrong direction, when it doesn't want it to be going
there. Now there was a piece of this that actually helped me out that that was I opening to me.
This is why it's important to actually go in and read the code. Like, I don't mean just like,
hey, what's the code definition? But like, what's the enable criteria? Like, when does it actually
look for this code? What pieces of information does the ECM have to see or not see in order to
actually even look for this code to be a problem? Okay, and especially when I'm dealing with a
challenging issue, I'm going to read through that stuff. And I'm sure you've heard case studies on
this podcast before where I will go into detail about the code information. And I'm really happy
when the manufacturer actually gives that to me, they don't always. But when they do, I'm going
to read that and take that into consideration. And it often opens up either a line of thinking or a
path for me to go in my diagnostics to figure out what's going on. So I'm not going to read it out
word for word, you can check it out in service information, if you want. But basically, you
have your enable criteria, which essentially says this code can set if the engine is running,
or if the engine is off, but the key is on and specific criteria are met. And that's a piece
of information that I actually used on this one that it can set key off. And it makes sense,
like, it's always going to be looking at the throttle position to see if it is in the position
it wants, which is again, kind of what this code is saying is like, hey, the throttle's not where
we expected it to be, or it's moving in the wrong direction of what we expect it to be.
But if you go into the testing for this, and it's circuit testing, which I'm not always
going to follow step by step. But I've mentioned on the show before, sometimes reading that can
give you a better idea of exactly what the ECM is looking for or not looking for in a particular
application. And again, this one seems pretty straightforward, like the throttle's not in
the right spot. Why? But I like to know, okay, what are they going to have you check? Because
that can lead you to what is the computer looking at? You know, or what is the computer using in a
certain situation to control the component or to monitor the component? Again, it's a two wire
circuit with an H bridge DC motor, relatively straightforward. But I still like to read through
this stuff to understand. And this show is brought to you by auto rescue tools and Isaac
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If you go through this, you can see it actually has you check a few things before you even get to
the circuit codes. Number or the circuit testing. Number one, there are a ton of other codes that
want you to make sure are not present in the ECM before you dive into this. And that's something
that's often overlooked when we have a big list of codes in a car is, hey, we might not want to go
after this particular code until we figure out this other one and service info may lay that out for
you like it does here. And we didn't have any of these codes here, but they have to do with like
the actual throttle position sensors not operating correctly. And then there's some voltage codes as
well. And it wants to make sure those aren't present. If those are present, okay, then you can
continue on. It wants you to look at throttle body airflow compensation parameter being less
than 90%. And so this is compensating for dirty throttle bore essentially is what this percentage
is. And it says if it's above this, then go to throttle body cleaning, clean your throttle body
wasn't the case here. Plus, we had a brand new throttle body, but the value was nowhere near that
high. So that was not what we're dealing with. Okay, you can move on with that. Then it wants
you to make sure, okay, that the tack motor parameters is enabled. And then it's going to
have you slowly press the accelerator pedal wants you to make sure that the computer is actually
trying to move this. And if that's all good, it has you jump into some actual circuit testing.
Now it has you test the, I'm sorry, no, there is one more part of this before the circuit
testing it has you go to the throttle body and make sure that's not bound up and stuck or not
moving correctly. So you're physically testing the throttle blade to see is this moving correctly
or not or is it binding? This one was when it was working, it was moving correctly. Again,
brand new actual OE part on this one. And then they have you get into the circuit testing and
really the circuit testing here is just looking at the control wires to the actual motor, right?
So you have two wires, they'll flip flop power and ground depending on which way we're moving the
motor or holding the motor. If you've never scoped one of the throttle motors or an H bridge circuit,
it's not just straight up power and ground held in one direction. It's going to be pulse with
modulated so they can not only move the throttle, but hold the throttle in whatever position in its
range. So realistically, if you're going to look at these circuits to see what they're doing, you
need a scope, whether that be an amp clamp or a voltage lead, that's the way that you're going
to have to view these to see what's going on. Okay, so with all that said, we're going to be
looking at the control to throttle motor for this particular code. It's not really saying anything
about the position sensors. And again, this one uses a sense protocol data line, which is a one
way communication from the throttle control to the ECM on this one. But really, it's not
saying that there's anything wrong with that. We need to look at the actual control wires. Okay,
so we'll do that. And here's where I'm getting into this actual diagnostic is I'm watching on
the scan tool and I'm just seeing if I can get it to screw up. Now the piece of information that I
gathered from the enable criteria that I'm actually going to use here is that this can set
key on engine off. And that's optimal for testing as far as I'm concerned, especially in the shop.
If I can get this to set key on engine off, it's just easier in general for me to test
enough to deal with a running engine. And so I'm going to try I'm just going to see what happens
if I operate the throttle key on engine off, can I get this thing to set? And it turned out that I
could I could actually get this to happen when I would go to command the throttle, or sometimes
when I would just cycle the key, I would turn the car off, I'd turn it back on, there's a
self test of that throttle that happens every single time that you key it up. And it would set
that code almost immediately. So I knew I was like, okay, I can catch this. Now here's the
interesting thing that happened while I was doing this, because I'm sitting there with the scan tool.
I'm watching this, you know, fail as I'm keying it up or operating the throttle. And I was looking
at data pits just to see what was going on with the throttle and this would happen. And I would
lose communication to the engine control module, like my scan tool would just be like,
nope, I'm not talking anymore, lost communication. I was like, that's weird. And that would be right
as the fault would happen. And I tried another scan tool just to see I was using Autel and
try topped on same thing, lose communication. And I actually got some communication codes to set.
Now, I don't know if those communication codes were ever present before. My guys are saying they
did not see them. The shop didn't mention them. But they were there for me, like actual lost
communication with engine control module during this time. I was like, that's that's strange.
Something something's going on here. And it definitely 100% has to do with when I operate
the throttle. And I proved this with the scope, because now I'm thinking like, okay, something's
happening with the network. And it's tied in with the throttle, which obviously is commanded by the
DCM. So yeah, I'm going to look at the throttle. And what I did is I put an amp clamp around the
wire going to the throttle body, just to see what's the current of this thing. And does it correlate
with what might be happening to my scan tool, which I'm just going to hook up to the CAN bus.
I can put a breakout box on the DLC, six and 14. That's all my scan tools communicating with the
engine control module. I'm just going to watch it when this happens. I know how to duplicate this
now, I can do it just sitting there, turn it on work the throttle, it's going to drop out for me.
So that's the throttle codes, but then also drops calm with the scan tool. And I see it happen. And
here's the interesting part. Amperage to the throttle motor never peaked over one amp. Like,
it was very small amount of current that was actually going to the throttle. And there was some.
Right when you'd either key it up or clear the code and activate the throttle, you'd see it.
But it was less than an amp going to this throttle body. But if you watched the data stream,
the communication, the actual CAN bus voltages, they got completely jacked up, like way out and
unusable signals. You could zoom in on them. They don't look like data packets. They're all over
the place as far as voltage goes. But only during that time, when the ECM is attempting to operate
the throttle. And again, my first thought was like, Oh, this thing's pulling way too much
amperage for one reason or another. But I'm also looking at the amp clamp going to the throttle
and seeing that it's definitely not the case. Okay, so one of two things are happening here,
I think, either the amperage draw moving the throttle or the attempt at moving the throttle
is affecting a ground or a power circuit that goes to the engine control module
and is dropping out that way. And I've seen modules that don't have
appropriate ground feeds cause issues on the CAN bus, right? It's going to use that same ground
that uses for everything else in order to operate the components on the board to talk on the CAN
bus and it can corrupt an entire CAN bus from a module that has a poor ground. And so I'm thinking,
okay, well, if the throttle is pulling too much amperage that has to go through the ECM,
that's straining whatever ground goes to it. And that could be what's happening here. So I did
some quick checking of that because it's fairly easy to do. Number one, these ECMs are actually
case grounded. So you could clip something to the case and check it that way. But there's also
just two pins that go to this that have ground, they're large pins on the connectors, easy to find,
put a headlight bulb or two on them and make sure that they actually can handle current,
which they could, no problem there. And the other thing was when I was looking at the waveform
of the actual throttle itself, it never spiked up high at all. Again, it was staying very low.
But I want to make sure that again, this isn't a ground issue. Also check my powers, the ECM,
all that stuff looks okay. All right, I need to focus back onto the throttle motor and here we go
with the throttle circuit itself, which if you read the DTC, it actually tells you to do this,
is to look at the two wires that go to the throttle motor, and you're going to be
ohm checking them not only to themselves across the wires, but to ground and power as well,
to make sure there's not some sort of short, which is what I ended up doing here is looking,
okay, do I have a short to ground on one of these wires? And it turned out I did. On one of the two
wires going to the throttle motor, there was a short to ground. And what this was causing was,
when the ECM went to operate the throttle, depending on, you know, which side of the
circuit was power or ground, it was going to be pulling either a ton of amperage from the ECM,
or maybe just moving the throttle in a way that it was not expecting. Again, depending on which
side we're talking here, but they're flip flopping back and forth. But at times, that straight shot
to ground on that circuit, which isn't fused, at least not up to the ECM, it's going to pull so
much amperage that it actually affected the output of the CAN bus. Now, I'm sure there was other
effects on that ECM as well, but that was like the direct thing that I could see in the moment.
And I know there's a connection between the circuit that drives the throttle and GMs and
the CAN bus. And some of you have seen this in waveforms. They look like garbage in a normal
running general motors product from this era. And it could be manipulated by activating the
electric throttle or reduced by unplugging the electric throttle. And that was just something
with the driver circuit and the CAN bus transistor and the ECM. There was a connection in these GM
modules that, I don't know, it didn't seem to exist in other vehicles. But you could see this
waveform and it looked like garbage. But if you went across the CAN high and CAN low, you actually
get a pre-usable waveform. Well, this was beyond that. It showed that kind of wavy waveform until
you went to operate the throttle. And it was completely out to lunch. Didn't look like anything
usable on a network. But it was straight shot to ground on one of those two circuits there.
So now we just have to find it. And that was relatively straightforward. Once we knew what
we were looking for is I actually just connected my own meter to ground, turned it onto the audible,
the beep option. So it beeps because I have continuity. And then I just wiggled the harness.
And what it ended up being was near the fuel rail, the harness had not been clipped down
properly to the upper intake manifold. And so the harness had rubbed through on the fuel rail.
And a single wire had been exposed, which was making contact with the metal part of the fuel
rail on the driver's side of the engine. And that wire went to the throttle body. So all the
amperage that's going through there was also going through the fuel rail, which was interesting
enough. But it was affecting the CAN bus because of a shorted wire to the throttle body. And it
didn't originally present itself as a communications problem. So I don't want to put that out there.
Like it was clear to the shop that it was a throttle body. But I mean, depending on how you're
looking at, this is a network problem, you know, in one way. And then yeah, I have a throttle body
code as well. But it was all due to the same thing. It's shorted to ground throttle motor control wire
on the fuel rail, pulling too much amperage on that circuit, which affected the CAN bus, pretty
crazy stuff. But we were actually kind of blown away once we connected all the dots of what we
were seeing. And, you know, we realized that this is our original problem with the throttle,
and then what it was causing on the network. So I thought that would be interesting to share.
You know, you don't always expect a specific problem to present itself in one way. And we run
into this a lot with, you know, control module systems and complex inner module communications
and networks. And these electrical systems, you don't always know how a failure will affect
that module and other systems. A lot of times it is unpredictable. But the more you do this,
at least you can kind of make the connection. And on this one, my experience with GMs and the
engine control modules, and that the throttle motor will affect the CAN bus waveform on these
General Motors products, it kind of made that connection in my head, like, oh, okay, so I could
see how a problem on this circuit could really affect the CAN bus output. Would it happen on
another circuit? I don't know. I don't think so, right? If the fuel injector circuit or the fuel
regulator circuit had had this same short to ground, would it affect the output on the CAN bus
same way? I don't know. But that's how this one ended up on this particular 2016 Cadillac Escalade.
So with that out of the way, thank you everybody for listening. I always appreciate it. I hope
you had a great 4th of July. But with that out of the way, let's get out there, start fixing the
world one car at a time.
About this episode
A real-world diagnostic case study centers on a 2016 Cadillac Escalade (6.2L) stuck in limp mode with reduced power and a check-engine light. The recurring code is P2101 (throttle actuator position performance), triggered when actual throttle position doesn’t match predicted position for over a second or when throttle control exceeds reduced-power limits. After multiple throttle body replacements (including OE) and even an ECM swap/cloning, the issue persists. The episode focuses on why intermittent throttle problems are hard to catch, how aftermarket parts can mislead, and how deeper code criteria and data analysis finally point toward the real cause.
This week on the show I share a case study on a 2016 Cadillac Escalade with a 6.2L that sets a P2101 in the ECM along with intermittent network issues. Are these 2 problems related? Listen to find out!
