Thank you very much Austen! Much appreciated!

Yeah you’re a dying breed. It’s only gonna help people that are already familiar with a few things

Thank you very much, glad you enjoyed it!

That’s wonderful! Thanks for sharing!

Thank you!

That’s awesome! Be sure to check power and ground to the module also. Thanks.

Most likely something got water into the connector. It would need to be diagnosed and you’d need to know what codes are setting. Thank you very much.

Well, it kind of depends on what the fault is when the fault messages present… if the trailer brake control module is communicating and reports a code for you to diagnose go after that. Or what I had going on in this video… The trailer brake control module wasn’t communicating at all and the module was faulty. I also see corroded wiring more often than anything else… About 6 to 12 inches from the module connector usually. If I were to suspect corroded wiring… I could disconnect both ends of the circuit and load test with a headlight bulb while measuring voltage drop to accurately measure determine whether that was a problem or not. Load test the power, ground, and LIN circuit. You can test with the ohm meter in the same way, but it won’t be as accurate because there won’t be any load on the wiring… that’s where a dealer tech will usually miss this because service information tells them to test everything with ohms. Intermittent wiring faults can be difficult to diagnose if it’s not acting up, but it takes a strategy of laying a trap where you think the problem may show up. Edit: another thing is that if the problem is intermittent it is unlikely to be a faulty module and more likely to be something like wiring or a trailer brake control switch code maybe. Thanks.

I’m not sure, but it’s a fast and easy way to be sure. It’s an expensive guess if they’re not testing it. Wiring faults are common enough on those that it should definitely be tested. Thanks.

I left the battery connected so I could do testing. Then I disconnected the battery when connecting the new one just to be extra safe and not get blamed for destroying a new expensive module lol. At 6:00 I take the connector off the module…It’s not a real close up view, but you can see how I remove it, there is a little red tab to pull out first as shown, usually dirt and dust really makes these connections stuck. Thank you for commenting!

G400 is located on top of the rear frame crossmember above the spare tire. Closer to the left side of the vehicle. If you have no power at the module and the fuses are good… Check for green crusty broken wires starting at the connector. It is common to find corroded and broken wires within 24” of the connector. Thanks.

This applies to the factory trailer brake system. Thank you

Try AllData DIY or something similar, you can purchase the service manual for a single vehicle at a pretty good price. Thanks.

When I started at the dealer I asked if they had a scope and they said no. I was browsing the tool room one day and found a dusty box labeled “NVH kit”… I opened it and found a BRAND NEW never-used pico and I was amazed to find they had this extremely powerful tool and not even known it nor using it. Turns out GM was only using the Pico for vibration analysis for years….yet if you order the lead set for it, you can use it as a regular scope. And that’s what I did. The NVH vibration analysis software is amazing also….I have a video showing the NVH software to find a dash buzz. In recent years GM has begun including Pico diagnosis in service information, but not much in my experience. Also they’ve begun a lot more Pico based training in the last couple years. Thank you for commenting.

No, this will not cause a check engine light. The remote start is probably disabled because of a stored engine trouble code even if the light is not on yet. Crusty wiring is common to cause the trailer brake fault message also so verify there isn’t a wiring problem before replacing the module. Thanks.

@DadsGarageDiagnosticSpecialist very helpful! I have no way to test the Lin, other than a ohm test, as mentioned in another comment. I love GM, but this is ridiculous. Let's change the location for 2025 ha ha. It's like, leaking 3rd brake light, back sliding windows, shark fin antenna. But I do love Gm. Lol

@@perrybeede9498 I covered that in the video 11:17 If the ohm test is ok and no shorts then most likely it’s the module yes.

@@DadsGarageDiagnosticSpecialist thank you!

@perrybeede9498 you are welcome

Well a high speed CAN network is a 2-wire twisted pair that operates at about 1.5V-3.5V and the signals mirror each other. There are also single wire CAN networks that operate at about 0V-5V. On CAN networks each module can individually communicate. A LIN network is a single wire network that operates at about 1V-11V and is set up as a master/slave arrangement with one master module supplying the reference voltage and the slave devices simply taking orders and sending information back to the master module. Thanks.

@DadsGarageDiagnosticSpecialist ok. To reiterate, the LIN network communicates to perform some specific task. Here it is telling the trailer module to actuate the trailer brakes. I have a another question about intermittent errors. I will ask in another thread. Thank you.

I have been seeing rotten corroded wiring fairly often as well… About 6 to 12 inches away from the trailer control module connector usually. 11:30 in the video I talk about testing the LIN circuit with a DVOM. Did you measure LIN circuit resistance end to end and also check for shorts? With the trailer power control, module, disconnected, and the key on… The LIN circuit should rest at about 1V lower than battery voltage…. That confirms the wire is intact and the master module is supplying the LIN reference voltage. If that is what you find, test resistance end to end and you may find a corroded wire on the LIN circuit most likely. Being at a General Motors dealership, you should also have access to the Pico scope. Thanks.

Will test again and will get back to you 👍

I also happened to do was use the GM trailer simulator. And all lights/ functions operated as intended.

@@petitogaming5659 sounds good. Also check out PIT5698C for some good information about LIN network diagnostics.

@@petitogaming5659 the trailer lights and the trailer brakes are on different circuits and handled by different modules. U1556 implies the chassis control module cannot communicate with the trailer brake power module. You said power and ground was OK so most likely the fault is on the LIN circuit.