MECHANIC: LIN bus failure on a 2010 Chrysler Town and Country · 12:22pm Oct 14th, 2023
Alrighty, kids, today we're gonna talk about a 2010 Chrysler Town and Country (not my van) with a set of seemingly simple symptoms but which turned into an adventure.
But first, y'all know what to do!
Customer's complaint was that the windshield wipers stayed on all the time, and that the turn signals didn't work. On this van—as with many modern vehicles—there's a stalk on the steering column that does many functions, and it's called a multifunction switch. In the case of this van, it controls the front and rear windshield wipers and both windshield washer pumps*, it controls the turn signals, and it controls the high beams and the optical horn (flash-to-pass).
And, none of those functions work. The wipers don't, either, but the customer said that he pulled the fuse for the front wipers to stop them.
*on this, as with many modern vehicles that have front and rear window washers, instead of using two pumps, it uses one pump and some valves, so if the controller spins the motor one way, it goes out the front; if it spins it the other, it goes out the back. The advantages are simpler wiring and either window can take advantage of all the washer fluid that's available [most cars with two pumps have the rear one mounted higher, so you've got some reserve for the windshield]; the downside is that you can't just switch the hoses when something fails on your $200 minivan that's hit four deer and isn't worth fixing.
You won't be surprised to discover that this wasn't the van's only problem.
I pulled the codes to see where that would take me, and this is what I got:
U0010: CAN interior bus
U1149: Lost communication with multi-function switch
U1109: Lost communication with LIN steering wheel controls
U0208: Lost communication with heated seat control module
U0161: Lost communication with compass module
U0201: Lost communication with left rear door module
For those who are new to these blogs, codes that start with U are communications/network codes (the other choices [currently] are P for powertrain, B for Body, and C for Chassis).
Now we gotta back up a bit and I'll explain some terminology. Some's gonna be Chrysler-specific, and some's gonna be general.
Earlier on, I said that the multifunction switch controls the wipers and the window washers and so on. That's not technically true; it makes a request to a different module which is who actually controls those functions.
Back in Ye Olde Times (the 90s), automakers saved on wires by multiplexing some circuits. That means instead of a traditional switch where you've got a wire in and a wire out, you have a series of resistors that pull down the voltage (or pull up the ground) a known amount and a computer to monitor that. You can then put multiple switches/buttons in, all with different resistances, and you only need two wires--a signal wire and a return wire. The computer then figures out which button you pushed, and tells the appropriate thing to take the appropriate action.
Fer example, the multifunction switch in this controls high/low/intermediate wipers, high beams on/off, right turn, left turn, front washer, rear washer, rear wiper—even if you only had one wire in, you'd need no fewer than nine wires out to run all those functions. Multiplexing is cool, but now microchips are cheap, so this little guy has four wires: a constant hot wire ('cause you can use the headlights with the key off), a key-on hot, a ground . . . and a LIN wire.
LIN stands for Local Interconnect Network. It's slow (by computer speeds) but it's simple and reliable, and it's just the thing for when you don't need super fast action, and where you don't have a lot of expected traffic on that network. If it takes a few tens of milliseconds for the turn signals to go on, that's okay. All you need is one wire. The controller of the network sends out a voltage, and much like the multiplexed switches of yore, it gets pulled down. This time it's digitally, so instead of a resistance, it sends a binary code saying what action should be taken.
You won't be surprised to find out that all the things that don't work are on the same LIN network.
Our computer was being slow, so it was quicker for me to pull the cover off the steering column and plug in the new multifunction switch, which—to my complete lack of surprise—didn't fix the problem.
As I tore into the vehicle, I started to discover the limitations of the service information I had. This LIN network attaches stuff from the steering wheel to the CCN, which then translates the message into the language the CAN bus knows, and most of that information then goes to the TIPM/FCM (Totally Integrated Power Module/Forward Control Module). For you not Chrysler people, that's the fuse box. Since all the fuses and relays are in a box, why not have the box make them go?
It's a barely-sealed computer that lives in the engine compartment, but there's no way that could ever go wrong.
Luckily, the TIPM is networked, and that means I can control stuff with a scan tool. It doesn't care who tells it what to do, it just does what it's told . . . and there'll be more to this as we go on; some of you might be having flashbacks to another Town and Country I blogged about some years past. Anyway, when it's told to turn on the turn signals, it does. It can control the headlights, it can control the horn, so this kind of localizes the problem.
In short, either the CCN isn't getting the messages, or it is getting the message but it can't translate it into something that the TIPM can understand. Since the CCN has set codes for the LIN bus, it probably works, but we'll keep it in the back of our mind. Usually when a networked module fails, it does not recognize that it has failed, so it wouldn't set communication codes. Sometimes this helps in diagnosis, but in this case only the CCN talks to this LIN network.
When it comes to wiring diagrams, they're often sorted by system. This is really useful when you're diagnosing one particular system, but it's far less useful when you're diagnosing multiple systems. The turn signals and headlights are on different wiring diagrams; the windshield wipers/washers have their own diagram, the cruise control has its own diagram, the horn has its own, the airbag has its own, the steering angle sensor has its own, and so on. In Mitchell, many of them just give little arrows with a label (i.e., Connector 1 terminal 3 white/green ➡ LIN bus; in Identifix they're often very circuit-specific so it shows most of the LIN wires but not any of the other wires.
And while I told you above that the CCN controlled the LIN bus, that wasn't evident at first; the SCM also has CAN bus wires, and so it could have translated messages.
In actual fact, the CAN wires were for the steering angle sensor; while a plodding (by computer standards) network might be okay for the remote radio buttons, for the ABS/Traction Control and the airbags to be the most effective, they need to know what angle the steering wheel is at and how fast it's turning. In the case of an accident, the airbag module has 15-50 milliseconds to decide which airbags to deploy and how hard to deploy them, it can't have some of the data it needs trundling in on a 10 or 20 millisecond delay.
The other confounding factor was that the SCM had eight connectors . . . probably. If a module has multiple connectors, they're labeled on the wiring diagrams, and the ones I had showed C1*, C2, C3, C4, and C8. Presumably there were also C5-C7, even if they weren't used.
Additional wiring diagrams revealed that the buttons, horn, and cruise control used one of the unaccounted-for connectors, and the airbag used the other two.
*C1 is actually the multifunction switch; while it is an individually-replaceable component, it's considered part of the SCM since it's attached to it.
Simple circuit tests showed that the LIN bus had continuity from any of its connectors to the CCN. I also tested the powers and grounds to the multifunction switch, and they'd light a headlight bulb, so they were good.
That's progress; we're down to two possibilities. Either the CCN can't translate, or one of the modules/controls/buttons on the LIN is stuck, shorted, grounded, etc. and that's blinding the network to any other messages.
You with me so far?
Before we go on, I will mention that the TIPM is smart enough to take its own actions if it doesn't get messages. As I would later discover, if it doesn't get any messages from the headlight switch, it will turn on the headlights. After all, it's safer to have the headlights on when they're not needed than to not have them on.
Can you guess why the windshield wipers were always on? The TIPM knows it can't talk to them, and it doesn't know if it's raining.
Alright, back to the diagnosis. Since the CCN is supposed to be outputting 7-12v (I didn't tell you that before, but now you know), and since the LIN will get pulled to ground as messages are sent (I also didn't tell you that), if I hook an oscilloscope to it, I ought to see the signals, if there are signals to be seen. Or maybe I'll see it's got too many volts or not enough volts, or maybe it doesn't actually get pulled to ground . . .
And what's even better, since there are several components which plug into the LIN and right now the only one I care about is the multifunction switch, I can just use a test terminal in the connector to monitor what the LIN is doing. I'm assuming (correctly in hindsight) if I diagnose why they multifunction switch doesn't work, that'll fix all the problems the van has.
I hook up, and I get a twelve volt square wave signal that drops to six or seven volts, which is right about in spec. And when I use the multifunction switch, nothing happens. Nothing changes, the voltage doesn't get pulled to ground.
It's unlikely, but maybe both the OE Chrysler switch and the new NAPA switch are both failed in the same way. A test lead connected to ground could tap on the LIN bus, I'd see it drop to ground, and maybe if I tapped it really quickly a couple of times it'd be a signal that was close enough to what the CCN was expecting to make it do something.
Which sounds kinda insane, but at this point I'm out of ideas. So I do that, I see the square wave get pulled to ground . . . and the left turn signal starts blinking.
Where there are the big dropouts, that's when I'm tapping it with a grounded wire.
And in fact, further experimentation shows that if I set the multifunction switch to do something (a turn signal, the rear wiper) when I tap at the LIN bus with my grounded wire, the vehicle does that thing for ten or twenty seconds, and then stops. I can tap it again, and it'll carry it out for a while. I presume this is programming; the CCN sees that the turn signal made a request so it tells the TIPM to turn on the turn signal. It never gets a request to stop, but it does stop seeing the signal, so after a programmed amount of time, it tells the TIPM to stop doing that thing (or else the TIPM reacts to not seeing a signal from the CCN as a sign to stop doing that thing; either way the result is the same.
Which means that I now know that the CCN is good. But I still don't know why the LIN bus is bad.
I'll add in a little aside here, at this moment in time I did have all the information to know why the LIN bus was bad, I'd just overlooked one clue.
I report my findings to my manger, and he suggests that I pull the LIN wire out of the CCN connector and out of the multifunction switch connector and just run a wire straight from one to the other. He also asks if I have everything disconnected on the network, and I tell him everything that I've found on the wiring diagrams (I've got a whole stack of them by now).
I think this is a stupid suggestion, but I do it anyway. While we don't have any of the correct terminals to make a proper jumper wire we do have some solid-core wire and if I jam it in the sockets just right, I can make contact between the CCN and the multifunction switch. It's kind of jank, but then the LIN bus is pretty robust and okay with jank.
The orange wire running across the steering wheel is my jank jumper wire.
As soon as I do that, all the functions of the multifunction switch work as intended. And, when I strip some insulation off that jumper wire so I can clip the oscilloscope to it, I see that the square wave's peak voltage is now lower, and I can see it pull to ground when I use the switch.
I can't show you a picture of all those things, but I can show you the difference between the two waves:
I cut off the scale when I took the pic, but you can see that the bad waves on the left side don't go as far down as the good waves on the right side.
A couple new tests with the multimeter reveal that the LIN bus is shorted to battery voltage, but that it's a very high-resistance short (185,000 ohms). Enough to drive the circuit voltage higher than it should be, enough that it can't pull the circuit to ground and thus can't communicate anything on that network.
Which means that my two options are wire a new LIN bus, or else I can pull the entire dash and find out where the rubbed-through insulation is.
Or else there's another component on the LIN bus I haven't found yet, and that's the one that's bad.
As I'm doing some more Identifixing, one thing catches my eye. Normally when you type in a code or a symptom, there'll be a list of results in a box, some diagnostic advice, and the number of times shops have reported that a particular thing fixed a particular problem.
Sometimes there's an extra little box at the bottom with a fix that doesn't fit the normal categories. And as I was scrolling down to see if I could get any better diagrams of the LIN, I found a box where a technician reported that a customer had brought a van in complaining that the wipers were on all the time, the turn signals didn't work, and the heated seats didn't work.
Do you remember above how I mentioned the heated seats being on the LIN bus? And how they had a communications code? 'Cause I didn't. They didn't show up on any of the diagrams I had, but when I looked for a heated seats diagram, they spliced in to the LIN bus at the same place everything else did.
If you don't know how heated seats work, it's basically like putting a toaster in a seat cushion. You've got wires that carry a fair bit of current and are constantly flexed. While all the stuff I've been working on so far has smol wires, the heated seats are powered by big, fat wires. If there's any component which is likely to leak some electricity where it shouldn't, it'd be the heated seats.
Now, for all the bad stuff I might say about engineers, Chrysler knows this, and would design the system in such a way that the electricity shouldn't leak into the LIN bus if the control module fails, but since the wires run under the carpet, the insulation on them might have gotten compromised and maybe just a little bit of it's leaking through.
The reason why the heated seats are on the LIN bus is so that the computer can choose not to operate them if the battery voltage is low. I presume this was a cheaper solution than having the heated seats module directly monitor the battery voltage [it's also possible that the strategy for the heated seats includes cranking up the alternator output, in which case the PCM needs to know if the seats are turned on]
Unplugging the heated seats module doesn't fix it. Unplugging the control panel for the heated seats doesn't fix it. Unplugging connector 200 under the dash does fix it, but I can't leave that one unplugged since lots of stuff goes through it. Like the signal for the starter.
"Well, we fixed your turn signals and wipers, but now the van won't start."
If, however, I just pull the LIN bus wire out of that connector and plug the connector back together minus one little wire, hey presto! Problem solved.
Well, mostly solved; obviously the heated seats won't work with that wire disconnected.
This is the point where the ball's tossed back in the customer's court. He's already in for a lot of labor:
Does he want us to go further?
It turns out the answer is no. He doesn't use his heated seats, or they've been broken for a while, or he'd rather have a cold rump instead of spending hundreds more dollars for me to pull up the carpet and inspect wires. Which, I'll admit, is the same thing I'd have done on my own van; remember, just above I admitted to switching washer hoses rather than spend the money to buy a new pump (or else it was the switch that was bad, I don't remember).
At the end of the day, not only did I fix the customer's complaint by simply removing one wire, I also fixed things he didn't complain about (the compass works now, as does the cruise control). And I learned an important lesson that y'all should take to heart: when you're diagnosing a LIN bus, or any other network, make sure you know all the modules and controls on the network. Even if it means slogging through about thirty pages of wiring diagrams . . . gotta catch them all!
LATE BREAKING UPDATE:
So it's been a couple weeks since I actually worked on this van; one morning when we went into the shop the van was back. The good news is that the LIN bus is still working; the bad news is the transmission isn't.
Yeah well that's probably not your fault so it's all good.
I have no clue why I am reading these blog posts. With zero interest in cars or trucks nomenclature of their parts is as clear to me as Croatian language. Still interesting to see troubles of modern complexity. Makes me wonder if all that progress was worth it. Things are not as easily maintained as before. My father was trained to repair washing machines and these days best you can do is order new parts, as they are no longer worth repairing.
Gotta love when you fix one challenging problem and shortly after something major goes ‘kablooey’... the money saved on the heated seats probably won’t make a big dent on the transmission failure bill unless it is a somewhat simple external part/wiring issue.
Yeah, I know very little about cars but I'm reasonably sure that a working transmission is Mission Critical.
Really hope that removed wire aint causing voltage, signal flow back from the heated seat modules thats taking the transmission IO port out of spec or something side current flow wise that way.
Reminds me of getting the computer to boot up when the mouse broke by shorting mouse port pins to ground with the screwdriver.
20 milliseconds response speed? Thats a full frame. Weird how modern computers still have problems switching between pixels at faster than microsecond speeds. No Duckhunt, even though Sonic requires Pixel perfect jumps?
Hmm.. that means I really got to work over the generic standardised pulg Ive been trying to think so it can handle intermittant partially shorted interupted ground lines also.
That everything on fire pic is a mood. Basically me at work a lot lol.
Lmao, awesome work! Love your posts
Nicely done.
Only mechanic-ing I've done of late is change a small tractor tire, then another one. Oh, and weld a door latch bracket back on. Lots more to fix yet on the loader... when I'm not under the weather, helping with the harvest, or both.
Y'know, windshield washers on tractors are awesome. Living in the future is so convenient, when stuff isn't broken.
5750456
We're here for the pony pics. That one pony with the desktop computer looks so confused.
5750455
Yup, nothing to do with us.
Also I didn't mention it in the blog, but the power sliding door communications failure also wasn't related; most likely the wiring in the door umbilical is damaged (common failure on them).
5750456
It's the cute pony pictures, that's how I lure you in.
I dunno, that's a tough question. There are advantages and disadvantages to the modern solutions, and there are features that cars now have that weren't possible using old tech, many of them safety features (i.e., you couldn't build a stability control system on an analog car). Computers also allow the engine management system to deal with faults--a computer can shut down electrical loads to make up for a failing alternator, and a lot of modern cars have engine management strategies to deal with overheating that will let you still limp the car along without severely damaging the engine.
And in some ways, it's easier to diagnose a lot of problems on modern cars, if you've got the right tools and knowledge. You wouldn't know that from reading these blogs, since I tend to focus on the weird failures rather than the straightforward ones: for example, I diagnosed a fuel mixture problem in under five minutes using the trouble codes the engine computer gave me, and a performance test I could do on the scan tool to force a couple solenoid valves to do what I wanted them to.
Maybe I should write a blog post about easy to diagnose failures. . . .
5750458
Yeah, and I always feel bad when something like that happens, even though it's not my fault.
It wasn't--besides the van not shifting in forward or reverse, it was very difficult to push it, like something had mechanically jammed in the transmission after it broke (my guess was something in the differential). We sent it out to a rebuilder, so I don't know what actually failed.
5750461
Yeah, if you want to do more than just rev up the engine, you need the transmission to work.
5750468
Nope, they're totally unrelated systems, and it was a mechanical failure.
I should look up what the network speeds on various networks on cars are. Like the fast ones are High-speed CAN and Medium-speed CAN (there might also be a Low-speed CAN, I don't know); there are various low-speed networks, and some vehicles also have fiber-optic networks, usually just for infotainment.
What the CAN networks use is twisted pairs of wires; one of them has the signal go high and the other has it pulled low, which gives them opposite waveforms. In theory, the CAN network can work if one of those wires has little to no signal.
(Some other mission-critical systems use a similar concept; for example, throttle pedal sensors and accelerator pedal position sensors use two potentiometers to show position, and they both output different signal voltages, so the computer can compare the two and make sure that it's really doing what you want to do.
They also often put on a ground-side bias so the computer knows that the ground is good, and sensors won't use the full range of voltages they potentially could; most sensors on a car are 0-5V, but the acceptable signal range is .5-4.5V; anything more or less is a fault.
Some sensitive systems also have deliberate 'noise' put in the signal in a regular pattern, and if the computer doesn't see that it knows something went wrong.
5750469
That's exactly how our work has been lately, too. And by 'lately,' I mean since about May, 2020.
5750535
Thank you!
5750549
Hopefully those things all went well
Right now would be the really busy time for you, wouldn't it?
Yeah, I bet. Yesterday I was wishing that the rear wiper on my van worked; I was driving down a bunch of wet dirt roads and completely lost rearward visibility for a while. When I stopped for gas and scrubbed the rear window off, I noticed that the soapy water was dirt road brown.
5750575
That's how I lure y'all in
He really does. That's how I was feeling as I was diagnosing this stupid van.
5751748
at least it's not my group any more now lol. we have our act together upper management on the other hand ...
5751750
Mostly. I had to fix a spring that had come undone in the latch, which was making the little tab not reset when the door was opened. Need to fix the hinges more properly so things line up like people expect. Unfortunately, not like a car door hinge, and the bad one is the most difficult to access.
Incredibly so. Had a breakdown on the chopper we were using to harvest corn last week-- finally got it fixed Friday. It turned out a grease line in a drive shaft from the zerk to the universal joint at one end broke, so it ate itself. It felt good to get everything back together and run everything at speed to test it. Got the combine harvester finished Saturday, just need to set the grain head up for soybeans so we can get those
whenif we get enough of a break in the rain.The loader is down again for a repair we knew was coming-- a massive (500+ pound) hydraulic cylinder that lifts the boom has a crack in the tube near one end. I really, really hope a local hydraulics shop can weld it up as a replacement is likely several thousand dollars. It's not a simple tube; there's lines and valves that are part of the thing. Annnnd the 'spare' loader is stuck in high range. I need to find a legit source for a service manual so I can trace wiring and fix what I can; it's over $300 for a service tech to show up.
5751784
Car door hinges are a pain, especially on older models where they need to be shimmed and can be moved in and out to get the trimlines to match up. I've done a few on S-10s, only 'cause I owned them and wasn't going to pay some body shop a hundred dollars to replace the pins and bushings.
If it opens and closes and doesn't leak in water when it rains, that's probably a good job, good enough until you start to go stir-crazy in the wintertime.
Yeah, there's nothing like equipment breaking when you need it. Or waiting for the weather . . . I can imagine how many farmers would pay for pegasi to make sure they get the right weather for harvesting their crops.
I've seen farmers working late at night more than once, getting the crops in when they can. Nothing weirder than to be cruising home from work well after dark and see off to the side a moving lightshow in the middle of a field.
Yikes, that sounds like a project. Even just moving the thing . . . we're lucky that most of the stuff we work on can be lifted by a mechanic or two, or a couple of fairly lightweight jacks or cranes (engines and transmissions, mostly, and fuel tanks if they're full). I can't imagine the fun of changing a tire on a tractor.
What kind of loader? It might be something you can find online, unless you've tried and come up dry.
5752371
Changing tire on a tractor is usually something we call a service truck in for-- they're equipped with a crane for lifting the big heavy thing. We do swap the rear wheels on one of our tractors out for narrow ones that fit between the planter rows each spring. That's a bit of a job, preferably three people, one in the skidloader that has pallet forks equipped.
The loader is a JCB 527-55. Which had a hydraulic line rub through and burst yesterday. That was a couple of fun hours removing the old and installing the new. I really hope I got the hoses routed correctly enough that they won't rub through as the boom telescopes in and out. A couple key spots were wrapped in chunks of an old tractor inner tube-- I keep one around for just this purpose.
Anyway, I need to check with the dealer first to see if they have a manual for sale, digital or paper, for a reasonable price ($200 or less). After that, it's a matter of figuring out what site I'd trust a credit card to.
It would be amusing to read about the experiences of an Earth Pony on, well, Earth, dealing with farming where the pegasi *don't* control the weather.