Ranger473

I don't have experience with the 2500 but I sure like my 3500. I sold my Ford F250 and bought the 3500.

2020 GMC 3500HD SLT L5P SRW I replaced the front rotors, brake pads, and brake pad life sensor (GM Part # 84702752) on my truck but the Brake Pad Life information screen is not updating. The owner's manual says it should sense the new sensor and brake pads and give me the option to reset to 100% but both front and rear brakes are greyed out and not responsive when I try and select one or the other. I have driven the truck around 40 miles with multiple starts and stops, including turning the truck off then back on thinking perhaps it takes time and cycles to update but there is no change. I pulled the tire and pads back off and verified the new sensor is installed correctly, I think. It seems like there is only one way to install it on the pad. I installed R1 Concepts OPTIMUM OE Brake Pads from Rock Auto. They seem to be a perfect match to the ones I removed (I have no idea if the old pads are OE). However, the pad on the sensor that (should) contact the rotor is about .25" from actually touching the rotor. - Like the pads are thicker than what the sensor is designed for. Does anyone have any thoughts?? I assume that when the brakes wear down to around 60 or 70% the sensor will finally contact the rotor and the system will start working...

UPDATE - SOLVED.....? My theory is that a little bit of dirt fell into the connector while I was installing the new module and that the dirt compromised the electrical signal. I pulled the connecter off the Trailer Lamp Control Module, used 25psi compressed air to blow out the male and female sides then used some electrical contact cleaner on both sides, followed again with compressed air. I made a shield out of a cereal box (see photo), put the shield in place, and then did the work. I placed the connector back on the module loosely and then pulled the shield out as I worked the connector up into place on the module. Now the Trailering App loads as intended. I am still suspicious that the cause of the blank screen may be a different and intermittent gremlin so I am cautiously optimistic. If the problem re-occurs, I will update this thread but if I don't do an update, it will because the blank screen has not re-occurred.

I just replaced the Trailer Lamp Contol Module to fix an issue where the #2 Pin (Tail Lights) was always hot. Now, when I select the Trailer App on the Infotainment Screen, the screen immediately goes blank or black. I can select the Home button below the screen and get the screen back and I can select any other app and it works correctly - I have tried them all. I have shut the truck off and re-started it several times to no effect. I have tried touching the blank screen in various spots to see if the app is running but I am unable to get any response. Any ideas?

SOLVED I replaced the Trailer Lamp Contol Module ($84.16 plus shipping and tax). Now the tail lights come on only when the lights truck lights are turned on. I replaced the 30A JCase Fuse, #63 TRAILER BATTERY, and now have 12V at the #4 BATTERY FEED pin all the time. This is the first time I have pulled and inspected a JCase-type fuse. I had pulled it before, inspected it, and thought it looked good. However, after replacing the trailer control module, I still did not have 12V to the Battery Feed pin. I pulled the fuse, popped the transparent cover off, and then I could see that the fuse had burned. I replaced the fuse and I have power to the trailer batteries. FYI - I cut open the old module but everything looked fine. I thought perhaps it might have gotten corroded or something but it was clean and dry inside so something on the circuit board failed. Thanks to everyone who contributed!

The Part number shown in the video has been superseded. And the price looks pretty good too at GMPARTSCENTER.net (when compared to the price mentioned in the video). It is due to arrive 14 Sept

Hey @gemarsh, thanks - that sure looks like my problem. I don't recall exactly where but I was under the impression the dealer had to "pair" the module to the truck but that didn't happen in this video. I am going to try the same thing and cancel my dealer appt. I'll update this thread once completed.

Yep, I provided the service writer a one-page summary with other support info. I have another packet for the tech and I am going to ask to speak with the tech when I drop it off. Thanks again for your time, interest, and ideas! I will keep this updated.

@64BAwagon Good idea about pulling the fuses. I pulled BOTH the Tail Lamp fuse and the Battery Feed fuse---the #2 Tail Lamps pin is still hot. With both fuses pulled. @gemarsh I swapped the relays as you suggested and no change. The #2 Tail Lamps pin is still hot with the relay out or with a substitute relay in place. FYI - It is a diesel and the Battery Feed cable is a direct shot off the side of the fuse block, as you said. And it is connected, the connection looks clean, and no corrosion. The #2 pin is getting power (12.7V) from someplace other than fuse 41 (Tail Lamps) or Battery Feed (fuse 63? - I don't have the fuse block diagram right here). I am thinking the problem may be in the Trailer Lighting Control Module located between the frame and the bed just forward of the spare tire. I have seen a YouTube video where weird lighting was the result of a corroded circuit board. The unit is sealed and needs to be tested by the dealer (my understanding). I have an appointment with the dealer next Tuesday. I made the appointment in person and provided a detailed explanation in writing of what needs to be corrected. I did not think I would be able to explain over the phone. I also am going to ask to speak with the tech when I drop it off to ensure he/she is very clear on what needs to be corrected. I am still open to ideas - I would love to identify and fix the problem with the community help I am getting here. In any case, many thanks to everyone for the ideas and discussion!!

I will keep this thread updated as I learn more and when I resolve the problem.

Thanks for all the replies and head-scratching! I truly appreciate it! Responses below: @gemarsh I don't see where his problem with not having 12v+ at the 7way, goes through the bcm looking at the schematic. I also don't see where he has said he checked the 30amp fuse for the 7way 12+. He might have 2 separate issues. I failed to mention that I had checked my fuses... Both the Trailer Parking Lamps #41 and Trailer Battery Battery #63 appear to be good. @64BAwagon My next step would be to follow that wire loom towards the underhood area checking for signs of alterations. I dropped the spare tire and followed it as far as I was able - it disappeared into the space between the bed and frame. It looks like it goes to what I think is the TRAILER LIGHTING CONTROL MODULE. The information I have is that becomes a dealer-level item to test and possibly Flash??? @UWSkier do you happen to know if the previous owner of your truck towed a camper? If so, did he use a Furrion pigtail adapter to make his backup cameras work? I don't know if it was used to tow a camper. The bed does not have any scars indicating a 5th wheel hitch was installed and there was not a dedicated Trailer set up in the trailering app. They could have deleted it but they didn't delete any of their mobile phones or data so it leads me to think pulling a trailer was not a prime purpose. It does look like someone spilled a bunch of red paint in the bed and then tried to hide it with a DYI bed spray... Red paint has dripped down under the bed in various areas. I have assumed it was a work truck but I really don't know. I understand what you are saying regarding the cameras - My 2016 F250 had to have the lights turned on to power the camera on my RV. The camera is always powered with this GMC in the current configuration. But if the wiring was modified for that purpose I am unable to find where it was done. Also, why disable the battery feed? It seems like it would require modifying the truck and trailer to ensure the camera is always powered. But who knows... Also good info to know regarding the adadpter from eTrailer. The camera works well know but when I get this issue resolved I might then need the adapter. Thanks! @UWSkier

Thank you for your reply and ideas - I have disassembled the bumper plug and tested the wire ends with the same result that I get from the assembled plug. Regarding the wire gauge - I am estimating and could easily be wrong about the gauge. The wire going into the #4 pin (Battery Feed) is significantly heavier than all the rest which aligns with 12V Battery Feed in my mind. It is the Red/Green wire in the photo. I made the "TOP" marking as a cue for the correct position when I re-assemble and to help me keep track of which pin is which while testing...

Thanks for your reply! I assumed that I would spot the modification with a good inspection under the truck - I certainly have dealt with people modifying lighting circuits on both trucks and trailers over the years, as, it sounds like, have you. I have never had a problem spotting the modifications or splices or even pins being changed on the plug. But no, all of the wiring bundles look like they are OEM with the PET Tape. The back of the plug is not modified and the heavy 6 or 8 (I think) gauge wire for the 12V Aux goes to the #4 pin (Battery Feed) But never has any power. The #2 pin is fed by a lighter 12 gauge wire but it is ALWAYS hot. I assume that the Battery Feed should only be hot anytime the "key" is on or the truck is running but in my case, the Tail Lamps pin is always hot. And, because the bumper plug and the bed plug are both wired the same way, the change is upstream from that and that wire bundle is certainly OEM with no ragged tape or bulges indicating a splice or modification.

EDIT: See end of thread for resolution. I have a new to me 2020 GMC 3500HD SLT. When I hook up to a trailer (this occurs with 3 different trailers and all three trailers work normally on at least 5 other vehicles) the tail/running lights come on and stay on. It does not matter if the truck is running, accessory mode only, or turned off or what position the light switch is in. When I connect the trailer plug to the truck, all of the Tail/Running lights come on and stay on. The ONLY way to turn off the trailer Tail/Running lights is to disconnect from the truck. It seems like the Battery Feed circuit has been wired to the Tail Lamps circuit. If they had been switched somewhere, I should see the #4 pin (Battery Feed) light up when tail lights are turned on but I never get a signal from the #4 p. The truck Trailering app tells me I have a problem with the Tail/Running lights. I do not get an error for the Battery Feed on the Trailering App. When I test the 7-pin bumper plug, the #2 pin (Tail Lamps) is ALWAYS hot. When I test the #4 Pin (Battery Feed), I am unable to get any power to it including when I turn the lights on. And my trailer battery does not recharge when driving. Left turn, right turn/brake, Electric Brakes, Reverse Lamp, and Ground all work normally. When I test the 4-pin plug and 7-pin plug located in the bed, I get the same results. The Tail Lamp circuit is always hot and I can never get any power to the Battery Feed pin (#4). I pulled the Bumper plug and it does not look like it has been altered. All of the wiring bundles under the truck also look like OEM work with no splicing bundles, etc. My questions are: Is there another junction / electrical box where the trailer wiring circuits could have been modified or switched? Is the problem in/with the K68 Trailer Lighting Control Module?