{"version":"1.0.0","episode":{"title":"344: GM MOST Diagnostic","url":"http://getcarcurious.com/episodes/344-gm-most-diagnostic","audioUrl":"https://www.buzzsprout.com/809423/episodes/18889744-344-gm-most-diagnostic.mp3","description":"This week on the show I share a case study on a 2017 Cadillac CT6 with no audio or display screen. This vehicle uses a copper wire MOST system that has unique diagnostic method. See the link below for more detail. https://diag.net/msg/m4fyw8nk9sugsj0ylwk7krbwkwWebsite- https://autodiagpodcast.com/Facebook Group- https://www.facebook.com/groups/223994012068320/YouTube- https://www.youtube.com/@automotivediagnosticpodcas8832Email- STmobilediag@gmail.comPlease make sure to check out our sponsors!SJ Auto Solutions- https://sjautosolutions.com/Automotive Seminars- https://automotiveseminars.com/L1 Automotive Training- https://www.l1training.com/Autorescue tools- https://autorescuetools.com/  "},"annotations":[{"startTime":26.8,"endTime":45.0,"type":"term","title":"used control module","url":"/glossary/used-control-module","quote":"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...","canonicalId":"term:used-control-module","priority":0.9,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"A used control module is a previously owned electronic unit (ECU/BCM/infotainment controller, etc.) installed as a replacement when new parts are expensive or unavailable. Because modules often store vehicle-specific data, they typically require programming, configuration, or cloning to work correctly."}},{"startTime":51.6,"endTime":97.2,"type":"company","title":"SJ Auto Solutions","url":"/glossary/sj-auto-solutions","quote":"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.","canonicalId":"company:sj-auto-solutions","priority":0.5,"confidence":0.95,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"SJ Auto Solutions is referenced as a specialist resource for used control module work. The host points listeners to their services and tech support for used module programming and related diagnostics.","simplifiedExplanation":"They’re a company that helps with fixing and setting up used electronic modules in cars. The episode mentions them as a go-to resource when programming is required."}},{"startTime":51.6,"endTime":97.2,"type":"company","title":"Tommy Oliva","url":"/glossary/tommy-oliva","quote":"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.","canonicalId":"company:tommy-oliva","priority":0.5,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"Tommy Oliva is mentioned as providing a cloning service for used control modules. The idea is to replicate the configuration/data so the module can be installed and function correctly in the target vehicle.","simplifiedExplanation":"Tommy is described as offering a service that copies the right settings from one module to another. That helps the replacement module work properly after installation."}},{"startTime":116.8,"endTime":134.2,"type":"car","title":"2017 Cadillac CT6","url":"/cars/cadillac/ct6","image":"https://upload.wikimedia.org/wikipedia/commons/4/46/CADILLAC_CT6_China%283%29.jpg","quote":"This week on the show, I'm going to share a case study on a 2017 Cadillac CT6. And the issue with this vehicle was no audio from the or response at all from the infotainment system.","canonicalId":"car:cadillac:ct6","priority":0.9,"confidence":0.95,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The case study is centered on a 2017 Cadillac CT6, focusing on an infotainment audio/display failure. This matters because GM infotainment systems rely on multiple modules and network communication, so the diagnostic path often includes module communication and configuration checks.","simplifiedExplanation":"This episode’s example car is a 2017 Cadillac CT6. The problem is that the infotainment system isn’t working—no sound and no screen activity—so the diagnosis has to go beyond just replacing parts.","imageAttribution":"Dinkun Chen (CC BY-SA 4.0)"}},{"startTime":123.8,"endTime":141.8,"type":"term","title":"infotainment system","url":"/glossary/infotainment-system","quote":"And the issue with this vehicle was no audio from the or response at all from the infotainment system. And you know, the obvious symptoms that were customer facing was that there was no audio, but then also there was nothing on the display screen...","canonicalId":"term:infotainment-system","priority":0.9,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"An infotainment system is the vehicle’s integrated electronics for audio, navigation, and the center display interface. When it has “no audio” and “no response,” it often points to power/ground issues, communication faults, or a failed/incorrectly configured controller.","simplifiedExplanation":"The infotainment system is the car’s screen and audio system. If it goes dead—no sound and no screen response—the cause is usually electrical or communication-related, not just the speakers."}},{"startTime":176.2,"endTime":182.3,"type":"term","title":"environmental identifier","quote":"and the radio is one of the modules that has the environmental identifier, which is a pin code","canonicalId":"term:environmental-identifier","priority":0.2,"confidence":0.6,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"An environmental identifier is a configuration value used by modules to ensure they match the vehicle’s operating environment and calibration/configuration set. The speaker says the radio has this identifier and it must match other modules, which is why mismatched modules can cause failures or incomplete boot.","simplifiedExplanation":"This is a setup/config value that helps the car’s computers confirm they’re all meant for the same vehicle setup. If it doesn’t match, modules may not work together correctly."}},{"startTime":182.3,"endTime":185.0,"type":"term","title":"TCM","url":"/glossary/tcm","quote":"essentially has to match all the other modules, ECM, TCM, BCM, SRS, cluster, airbag, I said SRS.","canonicalId":"term:tcm","priority":0.9,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"TCM stands for Transmission Control Module. It manages shifting and transmission behavior, and it typically needs to be compatible with the rest of the car’s module configuration.","simplifiedExplanation":"TCM is the transmission computer. It helps the car shift correctly and has to match the other vehicle computers."}},{"startTime":182.3,"endTime":185.0,"type":"term","title":"ECM","url":"/glossary/ecm","quote":"essentially has to match all the other modules, ECM, TCM, BCM, SRS, cluster, airbag, I said SRS.","canonicalId":"term:ecm","priority":0.9,"confidence":0.92,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"ECM stands for Engine Control Module. It’s the main computer that controls engine-related functions, and in many GM systems it must communicate correctly with other modules for the vehicle to behave normally.","simplifiedExplanation":"ECM means the engine computer. It talks to other computers in the car so everything can work together."}},{"startTime":215.0,"endTime":224.7,"type":"term","title":"infotainment display","url":"/glossary/infotainment-display","quote":"They still had no display on the panel, the infotainment display, and no audio.","canonicalId":"term:infotainment-display","priority":0.5,"confidence":0.85,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The infotainment display is the screen used for audio, navigation, and vehicle information. When it goes blank along with audio, it often points to a module communication or internal fault rather than just a simple radio hardware issue.","simplifiedExplanation":"That’s the main screen for the radio and other features. If it’s blank and there’s no sound, it usually means the car’s infotainment system isn’t booting correctly."}},{"startTime":232.4,"endTime":245.6,"type":"term","title":"internal fault code","url":"/glossary/internal-fault-code","quote":"there is a internal fault code in the HMI... where the actual fault is any of the modules that fail... can cause the whole thing to go down.","canonicalId":"term:internal-fault-code","priority":0.5,"confidence":0.86,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"An internal fault code means the module detected a problem within itself (not just an external sensor or wiring issue). The speaker connects this to the possibility that the HMI’s internal fault could cause the whole infotainment system to shut down.","simplifiedExplanation":"An internal fault code means the module itself is having trouble. That can cause the screen/radio to stop working even if the rest of the car seems okay."}},{"startTime":232.4,"endTime":240.3,"type":"term","title":"HMI","url":"/glossary/hmi","quote":"I did mention to them, hey, there is a internal fault code in the HMI, which is human machine interface module.","canonicalId":"term:hmi","priority":0.9,"confidence":0.93,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"HMI stands for Human Machine Interface module, which is the electronics that manage the infotainment user interface (screens/controls) in many modern vehicles. In this case, an internal fault code in the HMI is suspected to be causing the entire infotainment/radio system to fail.","simplifiedExplanation":"HMI is the module that runs the infotainment screen and user interface. If it has an internal fault, the radio and display can stop working."}},{"startTime":298.2,"endTime":304.0,"type":"term","title":"VIN","url":"/glossary/vin","quote":"changing the VIN number can be a little bit tricky. There are ways to do it.","canonicalId":"term:vin","priority":0.5,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"VIN is the Vehicle Identification Number, a unique identifier for the car. Many GM modules store the VIN and require it to be programmed correctly when replacing/using a used module, otherwise communication or feature activation can fail.","simplifiedExplanation":"VIN is the car’s unique ID number. When you install a used module, the car often needs that VIN entered correctly so the electronics will “recognize” the vehicle."}},{"startTime":392.0,"endTime":406.1,"type":"concept","title":"fiber OPTIQ cable","url":"/glossary/fiber-optiq-cable","quote":"...where it uses a fiber OPTIQ cable in order to transfer information for the infotainment systems. You see this on Mercedes vehicles, I think BMWs as well.","canonicalId":"concept:fiber-optiq-cable","priority":0.5,"confidence":0.85,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"In some European MOST implementations, media data is carried over a fiber-optic (OPTIQ) cable. Fiber optics can be checked visually (e.g., looking for light at the end), and that makes testing different from copper-based networks."}},{"startTime":399.1,"endTime":406.1,"type":"brand","title":"Mercedes","url":"/glossary/mercedes","quote":"You see this on Mercedes vehicles, I think BMWs as well. And they that that's not the same as this, although the system name is the same...","canonicalId":"brand:mercedes","priority":0.5,"confidence":0.8,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The speaker mentions Mercedes as an example of a brand that uses MOST with a fiber OPTIQ cable for infotainment media transport. This is relevant because it highlights that MOST testing differs between fiber and copper implementations."}},{"startTime":468.1,"endTime":474.4,"type":"concept","title":"CAN network","url":"/glossary/can-network","quote":"This one's going to be electrical signals, similar to a can network. But part of the reason I wanted to talk about it is there are definitely some differences between a most system and a can system.","canonicalId":"concept:can-network","priority":0.5,"confidence":0.85,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"A CAN network is a common vehicle communication bus used for many control modules. The speaker compares GM’s MOST electrical signals to CAN-like behavior to explain that, although MOST is media-focused, the troubleshooting can still involve electrical communication concepts.","simplifiedExplanation":"CAN is another type of communication network used in cars. The speaker is saying GM’s MOST copper signals behave more like an electrical network you’d think about when diagnosing CAN-style issues."}},{"startTime":508.9,"endTime":515.2,"type":"concept","title":"MOST bus","url":"/glossary/most-bus","quote":"And of course, that causes an issue with the most bus, we'll talk about that. But you can't communicate with the scan tool.","canonicalId":"concept:most-bus","priority":0.9,"confidence":0.92,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"MOST (Media Oriented Systems Transport) is a fiber-optic network used in many GM vehicles to carry high-bandwidth audio and infotainment data. When a MOST node (module) can’t communicate, it can cause symptoms like loss of infotainment functions and scan-tool communication issues.","simplifiedExplanation":"A MOST bus is the car’s “data network” for things like the radio and audio. If part of that network stops talking, the radio or infotainment can act up, and sometimes even the scan tool can’t communicate normally."}},{"startTime":571.1,"endTime":578.2,"type":"term","title":"radio","url":"/glossary/radio","quote":"But I never applied it in real life. So like I had the idea of the ring style communication that they use. And the radio is like the it's the central hub, it's the first module,","canonicalId":"term:radio","priority":0.5,"confidence":0.86,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"In many MOST-equipped GM systems, the radio acts as a key node that initiates and participates in the network’s communication. Because it’s central to the MOST ring, a radio failure can look like a broader network failure during diagnostics.","simplifiedExplanation":"In these systems, the radio isn’t just for music—it’s also a key computer on the infotainment network. If the radio fails, it can make other modules seem broken because the network can’t communicate the way it should."}},{"startTime":627.6,"endTime":633.7,"type":"term","title":"module offline","url":"/glossary/module-offline","quote":"if you have a break somewhere in that system, you have either, you know, an actual circuit issue, or you have a module offline. And that's the other important part is when if you have a module fail,","canonicalId":"term:module-offline","priority":0.5,"confidence":0.88,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"When a module goes offline, it stops participating in the network—often due to missing power, missing ground, or internal failure. On a ring network like MOST, an offline module can interrupt communication and cause multiple symptoms at once."}},{"startTime":691.1,"endTime":696.5,"type":"term","title":"oh meter","url":"/glossary/oh-meter","quote":"if you took the [691.1s]  oh meter and went across the two terminals, you would see continuity, you know, on can high to [696.5s]  can high, can low to can low.","canonicalId":"term:oh-meter","priority":0.5,"confidence":0.82,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"An ohmmeter measures electrical resistance/continuity across circuit terminals. Here, the speaker uses it as a diagnostic tool to show that CAN wiring can still show continuity across CAN High-to-High and CAN Low-to-Low even when module behavior differs from MOST.","simplifiedExplanation":"An ohmmeter is a tool that checks whether electricity can flow through a wire (continuity). The speaker is using it to compare how CAN wiring behaves versus MOST when modules are offline."}},{"startTime":880.5,"endTime":887.9,"type":"term","title":"master node","url":"/glossary/master-node","quote":"And this will be the surrogate most master is what they call it a replacement for the master node, because each module sets itself up as a node on this network.","canonicalId":"term:master-node","priority":0.5,"confidence":0.8,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The master node is the module responsible for coordinating communication on the MOST network. When the master can’t communicate due to a fault, the system uses a surrogate master concept to keep the network functional enough for diagnostics.","simplifiedExplanation":"The master node is like the “main coordinator” on the MOST network. If it can’t communicate because of a break, the system relies on another module to coordinate."}},{"startTime":928.7,"endTime":934.6,"type":"concept","title":"factory wiring diagram","url":"/glossary/factory-wiring-diagram","quote":"And honestly, looking at the factory wiring diagram, don't even bother with the after markets, looking at the factory wiring diagram with these really does help. It's a very nice visual.","canonicalId":"concept:factory-wiring-diagram","priority":0.5,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"A factory wiring diagram shows the official MOST network topology—how modules connect and where the ring is routed. The speaker emphasizes using the factory diagram (not aftermarket diagrams) because it provides the most accurate visual for locating a break.","simplifiedExplanation":"A factory wiring diagram is the official “map” of how the car’s wiring and modules are connected. Using it helps you trace the MOST network correctly when you’re trying to find where communication stops."}},{"startTime":939.9,"endTime":946.46,"type":"term","title":"RPO codes","url":"/glossary/rpo-codes","quote":"And then you can also utilize the diagrams and the RPO codes to figure","canonicalId":"term:rpo-codes","priority":0.5,"confidence":0.8,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"RPO (Regular Production Option) codes identify how a specific vehicle was equipped from the factory. In diagnostics, RPO codes help select the correct wiring/network configuration and module set for that exact vehicle.","simplifiedExplanation":"RPO codes are factory option codes that tell you what equipment your specific car was built with. That matters because different options can change which modules are on the MOST network."}},{"startTime":1023.2,"endTime":1033.2,"type":"term","title":"electrical diagnostics","url":"/glossary/electrical-diagnostics","quote":"If you're looking for education on module programming, J 2534, eprom work, key and immobilizer, electrical diagnostics or drivability diagnostics, Keith has a website L one training calm that's got over 60 hours of training videos on all those subjects and more.","canonicalId":"term:electrical-diagnostics","priority":0.5,"confidence":0.8,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"Electrical diagnostics is the process of tracing faults in wiring, power/ground circuits, sensors, and module inputs/outputs. In modern vehicles, many “non-engine” symptoms are actually caused by electrical issues or module communication problems.","simplifiedExplanation":"Electrical diagnostics means figuring out whether the problem is in the car’s wiring or electrical signals. It’s often about checking power, grounds, and what the computers are seeing."}},{"startTime":1092.5,"endTime":1100.0,"type":"concept","title":"module communication","url":"/glossary/module-communication","quote":"I never had to dive into a circuit issue with the most bus. So on this car, all the modules that were involved did communicate. Okay. And there was quite a few this thing was fully loaded. It has like the DVD or the video","canonicalId":"concept:module-communication","priority":0.5,"confidence":0.85,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"Module communication refers to how vehicle control units exchange data over one or more networks (CAN, LIN, MOST, etc.). In diagnostics, confirming that modules “communicate” helps narrow the fault to a specific network segment, module, or power/ground issue rather than a total vehicle failure."}},{"startTime":1420.0,"endTime":1425.18,"type":"concept","title":"datapids","url":"/glossary/datapids","quote":"...once I understood how it works, and then I use the datapids and the scan tool and the radio, and it basically just","canonicalId":"concept:datapids","priority":0.5,"confidence":0.8,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"Data PIDs (parameter IDs) are live data items reported by the vehicle’s modules to the scan tool. In network diagnostics, PIDs help confirm whether modules are communicating and whether the system is reporting the expected network status after repairs or configuration changes.","simplifiedExplanation":"PIDs are live readings the scan tool can pull from the car. They help confirm which modules are talking and what the system is reporting right now."}},{"startTime":1462.8,"endTime":1469.9,"type":"concept","title":"module is offline, it essentially is going to open the network","url":"/glossary/module-is-offline-it-essentially-is-going-to-open-the-network","quote":"Again, because once that module is offline, it essentially is going to open the network. Or if it's a problem, you know, you would want to bypass it and the rest of the system can turn on and operate without a particular component.","canonicalId":"concept:module-is-offline-it-essentially-is-going-to-open-the-network","priority":0.5,"confidence":0.84,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The speaker is explaining a diagnostic behavior of the media network: if a module goes offline, it can interrupt the network path and prevent communication. That’s why bypassing the module with jump connectors can restore network operation and narrow down the culprit.","simplifiedExplanation":"If one device on the car’s media network stops working, it can break the communication path for everything else. Bypassing it helps you confirm that the rest of the network is still healthy."}},{"startTime":1502.6,"endTime":1514.6,"type":"term","title":"butt connectors","url":"/glossary/butt-connectors","quote":"and they did a pretty poor job of putting a series of butt connectors in, just like the heat shrink butt connectors. And it was actually on both of the most bus communication wires.","canonicalId":"term:butt-connectors","priority":0.9,"confidence":0.92,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"Butt connectors are splice connectors used to join two wires, often with heat-shrink insulation. The speaker found “heat shrink butt connectors” installed poorly, and that matters because a bad splice can create intermittent opens/shorts that break network communication.","simplifiedExplanation":"Butt connectors are wire splices that connect two wires together. If they’re crimped or sealed badly, the connection can fail and cause the car’s electronics to stop working."}},{"startTime":1576.5,"endTime":1583.9,"type":"term","title":"oscilloscope","url":"/glossary/oscilloscope","quote":"But anyways, I did try to do some scoping of the network to see if I could, you know, manipulate the circuit and get things to happen.","canonicalId":"term:oscilloscope","priority":0.9,"confidence":0.95,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"An oscilloscope (scope) measures voltage over time, letting you see waveform shape, amplitude, and timing. Here it’s used to evaluate the MOST communications network and to understand why probing can affect the system.","simplifiedExplanation":"A scope is a tool that shows how voltage changes over time. It helps you see what the car’s electronics are doing electrically."}},{"startTime":1710.4,"endTime":1714.8,"type":"term","title":"wiggle wires","url":"/glossary/wiggle-wires","quote":"And you can actually watch this in real time, if you're trying to find an intermittent connection, wiggle wires, watch the scan tool, that's the way to do it.","canonicalId":"term:wiggle-wires","priority":0.5,"confidence":0.9,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"“Wiggle wires” is a diagnostic technique where you gently move wiring/connector harnesses while monitoring live data to provoke an intermittent fault. The host pairs this with watching MOST-related scan tool PIDs to confirm a connection issue.","simplifiedExplanation":"This is a hands-on test: you gently move the wires and connectors while watching the scan tool. If the problem shows up, you’ve likely found the loose or failing connection."}},{"startTime":1839.1,"endTime":1848.5,"type":"concept","title":"disconnect the instrument cluster and disconnect the amplifier","url":"/glossary/disconnect-the-instrument-cluster-and-disconnect-the-amplifier","quote":"That could happen if, you know, a harness is smashed somehow or another, I would have to disconnect the instrument cluster and disconnect the amplifier and then test for a short together.","canonicalId":"concept:disconnect-the-instrument-cluster-and-disconnect-the-amplifier","priority":0.5,"confidence":0.86,"source":"hybrid-fuzzy+gpt-5.4-nano","data":{"explanation":"The speaker describes isolating modules (like the instrument cluster and the amplifier) to accurately test for a true short on the MOST bus harness. This is a practical diagnostic strategy: remove module internal circuitry from the measurement path before concluding the wiring is faulty.","simplifiedExplanation":"To find the real problem, they suggest unplugging key modules first—like the instrument cluster and the amplifier—so your meter can test the wiring itself. Otherwise, the modules can make the test look like a short when it’s not."}}],"speakers":[{"id":"s1","name":"Sean Tipping","role":"host"}],"transcripts":[{"url":"http://getcarcurious.com/episodes/344-gm-most-diagnostic/transcript.vtt","type":"text/vtt"}]}