This Ethernet "primer" post has sitting on my desktop for a few months now, as a follow up post to MOST and while it is no means a complete work, it has grown to a stage where it may provide some useful insight to those who are interested.
Caleb Mohler recently presented an Ethernet-based system concern, so perhaps it is timely to add some information that may be put to use as more of these systems are encountered.
A relatively recent change to GM vehicle infotainment networks since 2017, was the implementation of Ethernet networks. Ethernet for automotive applications is based on the OPEN Alliance (One-Pair Ether-Net) standard utilizing single twisted pair of wires from a network switch module to the end point modules.
For those who are interested, a relatively light read white paper on infotainment networks can be found here: support.ixiacom.com/sites/default….pdf
For the purpose of this post, Ethernet will be the sole focus. However, during diagnostics, other power, ground and communication networks may be involved and necessary to investigate and test.
General Ethernet Overview
Communication capability is up to 100 mbps, twice the speed of MOST 50 that has been used on GM vehicles since ~2014. Notable, is that automotive Ethernet conductor and termination construction is different to that of the traditional 4 wire Ethernet used in most personal computers, due to automotive systems being subjected to much harsher environments atypical of non-mobile networks, to include but not be limited to extreme thermal ranges and vibration stresses.
When equipped, these modules are connected to the A11 Radio via Ethernet:
- Instrument Panel Cluster - Amplifier - Infotainment - Telematics - Heads Up Display
Figure 1 provides a general overview of the infotainment and other associated modules layout, as fitted to … GMC Terrain models equipped with RPO IOS, IOT and IOU Infotainment systems. Other models are similar. An IOR Ethernet infotainment network is used on Bolt and also on 2019 MY Cruze, where it replaces the Bring Your Own Media 2 (BYOM 2) system. Those will not be discussed here.
Figure 2 shows a typical representation schematic drawing of the infotainment system related Ethernet wiring on GMC Terrain … Model Year), RPO code IOU.
Infotainment 3.x systems use Ethernet to transfer information between the radio and other infotainment modules. Each module utilizes an Ethernet connection, (port), having a dedicated 2 wire circuit to the A11 radio which is the Ethernet master and is responsible for all Ethernet diagnostics.
Unlike MOST bus, there are no diagnostic jumpers to install to bypass a suspected failed module, since the network topology is not a ring. Instead, it is relatively simple module to module transfer of data, with only the master (A11 Radio) serving as a network switch and the receiving module as an end point. E.G. A11 Radio to K73 Telematics module, A11 Radio to T3 Audio Amplifier and A11 Radio to P16 Instrument Panel Cluster.
On some vehicles, the radio may be referred to as the Centre Stack Module (CSM) based on location, but is identified in Service Information as A11 radio. As used in the Terrain, this is a remote mounted module, located behind and to the lower right of the glove box, near the right kick panel, suspended in a plastic carrier.
Ethernet can communicate at up to 100 Mb/s on each connected port and there are typically up to 3 connected devices in GM Global A vehicles. To handle a large amount of data and data of different types, the system uses Audio Video Bridging. AVB retains a portion of the available Ethernet bandwidth in order to accommodate timing instructions that allow for video and audio play back at specific times. E.G. when the audio is sent to the amplifier, it contains a set of specific instructions for each channel to ensure that the music is played back properly synchronized between the speakers.
The Ethernet has no connection to the Data Link Connector (DLC) and similar to the MOST Network, it’s controlled and diagnosed by the radio as the bus master. However, there are several data parameters in the Ethernet connected modules that can also be utilized to aid in diagnosis. These modules do connect to the GM LAN for diagnostics and other requirements.
Diagnosis of the Ethernet communication is DTC based, with specific DTCs that align with Ethernet link status and signal quality data:
DTC U18AF - Lost Communications with Telematics (OnStar)
DTC U18B0 - Lost Communications with Instrument Cluster
DTC U18B1 - Lost Communications with Audio Amplifier
DTC U18B2 - Lost Communication with Rear Audio Control Module
DTC U18B3 - Lost Communications with Navigation Control Module
DTC U18B4 - Lost Communication with Radio
DTC U18B5 - Associated with Ethernet fault on hybrid/electric models
Each module connected to the radio via Ethernet constantly monitors the connection, and the related data can be viewed using GDS2. For each Ethernet connected module, AMP, the IPC and the OnStar module depending on configuration, the radio reports Ethernet Bus Status as either Up or Down and also lists Ethernet Signal Quality, scored out of a possible 5 (with 0 being no communication). Ethernet circuit faults required end to end circuit verification before ECU replacement. A good connection typically rates 4-5.
Reportedly, Service Information (SI) will eventually contain a Port Map to show which modules are linked to each port. At this time, the Ethernet data list information is used to identify the ports. Some anomalies have been experienced in the number of displayed ports, depending on which version of GDS 2 was used on the same vehicle. This tends to result in the technician relying solely on DTC diagnostic steps and wiring schematics, while monitoring changes in port status and quality may serve as a verification of restored function.
The A11 Radio requires an internet connection through the OnStar LTE in order to support available cloud based features including:
App Store / Apps
Essentially, the K73 Telematics Communication Interface Module functions as a modem, with the A11 Radio controlling all related systems functions as a network switch, similar to how a PC Internet connected network functions.
Figure 3, depicts an end view representation of the A11 Radio connections, as fitted to Ethernet equipped … GMC Terrain models. With the radio installed, it's orientation in the carrier allows these connections to readily accessible from below in the right front corner of the passenger foot well, on Terrain models.
Note: For 2018, MOST Bus and BYOM 2 infotainment systems were available options on the Terrain. However, for 2019 MY, from recall there are only Ethernet options listed for the same vehicle. These are: IOS, IOT and IOU. So, for diagnostics it is critical to identify the infotainment system early on, using the vehicle build information to identify the Regular Production Option (RPO) codes. Product branding such as MyLink®, Intellilink® and Cue® represent only the visual appearance of a vehicle infotainment system to the Chevrolet, GMC and Cadillac owner and play no part in the technical aspect or function.
However, component codes as used in this post, such as A11, K73, T3 etc, are common across all vehicles with fitted with BYOM, MOST 50 and Ethernet infotainment systems.
Ethernet Wiring Repair
Early during production, if an Ethernet cable was found to be damaged, the repair strategy was to replace the entire harness that contained the Ethernet cable. So, for example if replacement of the A11 to K73 Telematics (OnStar) Ethernet cable was required, the entire CSM to OnStar harness must be replaced. The plan for Ethernet service cables to be released, and once available, was to allow replace the just the Ethernet cable and overlay it on the harness. There is be no service of the Ethernet terminals, so no terminals or crimping tools will be offered. As with other high speed data cabling and similar to fiber optics, there are necessary steps to proper installation of replacement cables, such as when the antenna cable in Figure 4 is overlaid along a vehicle harness.
It is necessary to observe and practice maintenance of looping excess cable to maintain a loop greater than 5 times the diameter of the cable diameter, with both acceptable and unacceptable being shown. This might be a challenge for those of us who have difficulty tying our shoe laces! Contrasting colour insulation tape was used to identify insulation and retention to main harness to eliminate interference. For the nitpickers, the tape work is a bit loose, purely since the tape had been sitting around for over 25 years or so.
While initially there was no repair of Ethernet twisted pair and nothing suggests the contrary, terminated leads are available.
Figure 5 shows the now widely-used FAKRA style connectors as fitted to antenna cabling on current GM BYOM, MOST and Ethernet systems, with the four connectors applicable to the GMC Terrain of focus in this post. The upper right connector is identified as "Cu" (Curry). Each colour connector is indexed differently.
Many the Ethernet circuit connections use a newer terminal that is smaller than previous terminals used anywhere in our vehicles. This terminal is known as the Mini 50 or the Nano 50 depending on the connector manufacturer and/or time of introduction. Along with previously used release tools, there is a new release tool and terminal probe to support diagnosis and service of these terminals. See Figure 6, Figure 7 and Figure 8.
Two new tools have been released for the service of the Nano-50 terminal connectors, the EL-35616-58 Test Probes and the EL-38125-58 Terminal Release Tool.
The release tool blade (rectangular cross-section) is inserted as shown, to depress the terminal retention tang which protrudes into the entry canal. The terminal connection cavity has chamfered entry port to allow ease of terminal engagement with its mating terminal.
While the new 0.5 mm terminals (identified by Type II in SI table) are utilized at the A11 radio and K73 Telematics Ethernet terminations, 0.64 mm terminals are used in some connections such as the T3 Audio Amplifier terminations. Thus, it is important to correctly identify the connector that is being serviced or inspected, by the using the infotainment system RPO code and appropriate wiring schematic. The J-35616-64b is used to probe 0.64 mm round and square section terminals. J…A is used to release 0.64 mm (Type I terminals). Depending on the connector, the TPA is "staged" and the TPA then acts as a guide to install the -215A release tool. It can be a bit tricky getting the tool in straight to engage the retention latch, so removal of the TPA to allow improved visibility of the latch is an alternate approach.
Door chime present (L/F door speaker)? - If yes, amplifier is powered up, communicating and able to output to at least one speaker.
Verifying customer concern - Check all inputs - various radio antennas and all radio controls, APPs, ability to register etc.
A good place to start is the Diagnostic System Check - Vehicle, in order not to miss diagnostic opportunities. Whether technicians follow this path is basically down to level of expertise and experience. I'd certainly recommend that less skilled technicians go this route, while experts may take another path, knowing that their own preliminary investigations have fulfilled the needs associated with the DSC-V path.
Check for DTCs - Always begin a scan with Vehicle DTC check and focus on any loss of communication U DTCs first, verify power, ground with DMM and complete basic circuit system testing and verify the associated Ethernet bus wiring for high resistance/opens, shorts to voltage, shorts to ground and shorted together. This is very basic stuff.
Note: On 2018 MY Terrain, DTC 125B 04 may be present in GDS 2 as shown in Figure 11. Information for this DTC related to Digital Audio Broadcast (DAB) can be found in PIC6291, which identifies DTC 125B 04 and other DTCs, to be ignored as they are non-applicable to various vehicle platforms.
Figure 12 shows a Terrain with U18B1 and U18B4 set (accessed via the "Details" button). This vehicle is not equipped with the modules that are identified as not communicating (red & white circle). All other modules are functional and both the radio and amplifier modules in which DTCs have set, are awake as denoted by (yellow triangle). However, they are unable to communicate with one another, resulting in each module setting a non-communication DTC.
During a failure the switch runs the Active Cable Test and determine the type of failure the link is experiencing, while the end point module posts a general failure DTC. There may be some variance regarding exactly how the DTCs display when certain conditions are exhibited. For example, U18B4 sets with regularity when inducing specific Ethernet faults, while U18B1 appears to set infrequently under the same conditions.
This is where suspect connector terminations and wiring integrity is a primary diagnostic focus, but it may also be that the Ethernet connection inside a module could still be at fault. Routine diagnostic practices for testing for end to end open circuits, shorts to ground, shorts to voltage, shorts across the bus etc, are the norm.
The schematic in Figure 13 shows the relative simplicity of the circuit in question, with the fault isolated to the twisted pair Ethernet, associated terminations and connectors through the A11 Radio (switch) to T3 Audio Amplifier (end point module) using simple end to end topology. In other words, each end device has a dedicated link with the A11 Radio, so end devices are independent from one another, while each is connected to the A11 Radio.
Identify the affected Ethernet bus by "mousing" or "hovering" over the schematic to identify the bus # and other relevant details, such as circuit #, the bus information becoming magnified when hovering over the # as shown. With connector, conductor and bus information in close proximity, precise manipulation of the mouse to retrieve the desired information, is necessary.
Mousing over the schematic circuit 7215 identifies the affected Ethernet Bus # 6 + conductor path. Both the A11 radio module and T3 Amplifier Module were both functioning, but unable to communicate with one another. No shorts to ground, together or to voltage were noted during testing and end to end testing revealed an open circuit at the point indicated on the schematic.
Figure 14 shows the same Terrain with the bus repaired. DTCs have gone to "History" Note the aforementioned erroneous DTC for the antenna and also the front video output signal, that was a byproduct of performing diagnosis.
Reportedly, an Ethernet port assignment table is forthcoming to SI at some point. However, an anomaly with port identification in GDS 2, currently leaves port identification less useful than previously believed.
The GDS 2 screen capture in Figure 15 shows a 2018 Terrain with RPO IOU, before a GDS 2 update in late 2018.
The GDS 2 capture in Figure 16 shows the same 2018 Terrain after a GDS 2 update. Note that the number of ports listed has now increased from 3 to 5, while nothing has changed on the vehicle.
Also, note that port status and signal quality no longer aligns with previously supplied information, where a port that was communicating properly was UP with a signal quality of 4-5 and a port that was Down, had a signal quality of 0.
Upon subsequent investigation, the response was "GDS2 data shown on the Terrain has been unpredictable and cannot currently be used to validate the Ethernet." So, focus for diagnosis is on the schematic and basic diagnostic tests.
FWIW, according to feedback from a few technicians there have been some "bad" radios encountered reported to exhibit blank screen or other conditions at PDI or shortly after. Any and all attempts to initiate or restore function did not resolve the concern. A11 radio module replacement only, apparently fixed the issues. I can confirm knowing of one extremely capable and reliable technician, who experienced this exact scenario on a 2019 Colorado, that was eventually resolved with replacement radio.
From reading elsewhere it appears that a possibility is that Ethernet initialization during manufacture, may not have been successful.
It is normal to expect the diagnostic technician to perform thorough circuit testing, terminal pin inspection, tension etc, prior to requesting a replacement module.
Note: When viewing a description of the condition in GDS 2, it appears that there will be only two possibilities displayed, open or shorted to ground. GDS 2 does not identify shorted to voltage or shorted together conditions, so if a short to ground condition is not identified during testing, performing tests for short to voltage or conductors shorted together will identify any faults of those types. The diagnostic table does however, identify the possible shorted conditions.
Martin, Great post! Very in depth, thanks for posting this!
Thanks Dean. I've been gathering "tid bits" here and there of information that I hope is relevant, so feedback and constructive criticism is always appreciated. Brian commented about how these connections and terminations might survive in the real world of automotive "professionals". Acres of plastic trim secured with a myriad of near single use claw type fasteners can make it a bit of…
Wow that is a great amount of information. Thanks for sharing. Any word or personal experience on the durability of the connectors? It seems with every thing getting smaller that we have more connection issues due to collisions and rough handling from techs.
Thanks Brian. The whole idea of sharing here, is that we all have an opportunity to become better informed of what we might encounter during diagnostics of systems being introduced at rapid pace. When I first learned of Mini 50 and Nano 0.5mm being adopted, I had the same concerns. There was talk of special connectors, since PC style Ethernet connectors would not be robust enough in the…
Hi Martin, thanks for continuing your great work in research for Ethernet. Loved your work from few years ago on MOST!
Thanks David. Now that we've Ethernet around for a couple of model years and experienced some resulting failures, we have had some time to get used to the diagnostics and data. It's been a learning curve determining some faults and/or erroneous data and failure trends. While wiring and connections usually gets the most focus during diagnosis due the disbelief that modules fail, some component…
Great post, thanks for taking the time to share! Does anyone know what specs a scope will need to test these networks? It seems inevitable to me that we will see ground and voltage leakage issues like any other network, and to me the scope seems like the best route to see the weird ones... which is what I always seem to get on mobile calls. I am trying to be ahead of the game and looking to buy…
Thanks Matt. Nothing in the automotive realm of scopes. At the engineering and design level, for sure the equipment is needed to ensure compliance standards are met etc, etc, but it would be a very expensive proposition to purchase equipment simply for interest's sake, just to to examine the data that nothing can be done with at the technician level. However, I found a few links that might…
Thanks, Martin. I know it seems excessive, but a friend and I do all the weird network issues for the area. A year ago one truck had a network issue, they were quoted 19K for an aftertreatment. 16 hours of diag, which was all paid for by the customer.... but a bad ground caused corrupted data. Meter voltages would be "normal". So, we are looking at around 10 to 12K for a scope, but we will share…
No problem Matt. While still wrenching daily, my nickname at the shop was "Mr. Gadget", for all of the speciality tools and test equipment I owned, either purchased or fabricated. So, I can well appreciate the desire and quest for knowledge that can take it to a level beyond what most of us will need. I recall when we received the first Duramax truck in 2001, staying at the shop, scanning and…
Absolutely, time is never wasted learning and doing research. Spend a day doing research, save hundreds of hours in the future. Time is money :)
Martin, Very nice write up. It is evident you have spent a great deal of time working on this. Again the OEM is introducing more complexity to the automobile. We have many technicians struggling with basic electricity, now they have to understand why large or small loops may introduce problems into a system. I feel sorry for the next guy. If we are to expect our technicians to use the finesse…
I agree that many techs are struggling with basic electricity. I am on a mission to help the average tech gain a better understanding of the basics. The best part is I am learning more along the way. Write ups like this one are invaluable for all of us to learn.