Thunderbolt

If you need TPMS on your trailer look at offerings from TST Truck https://tsttruck.com/shop.html They work well, get the flow through sensors but only if you have metal valve stems. I did 10,000 miles in 2019 with these on the 2019 truck and trailer. Nice that you don't need to check air pressures every day. Just turn on the color monitor and all of the sensors report in, takes a few minutes but a lot easier than crawling around underneath the RV every day.

Not all trucks are equipped with the option. The ECU as mentioned earlier is a small rectangular device mounted on a plastic bracket mounted behind the rear license plate. There are two devices mounted there, the small one is for keyless entry and the larger is the ECU for the TPMS. If it has the larger one and the truck comes with 4 sensors to be mounted inside the trailer tires you are probably good to go. Unless they did something in the 2021 model year different than my 2020 it still will not pick up the trailer wheels reliably without modification. Pretty sure you will need options U1D and PTT. Look for them on the build sheet.

Yes, they are stamped 433.920 and so is the ECU on the truck. If you are thinking booster or repeater so did I. I have the system that I installed on my 2019 truck that did not have the TPMS from the factory. It came with a repeater and I installed it underneath the front of the RV which is where I had previously installed it last year for our trip out West. It did not improve the reception. I spoke with the tech support at TST Truck the manufacturer of that system and he said that their protocol was different from the GM protocol. He said think of it like a wifi password. By the way the ECU and the sensors are stamped Schrader which I learned has been sold to Sensata. I spoke to the Schrader/Sensata tech support rep about these problems and he was in contact via email to the folks in the UK and they were eager to work with GM to resolve the issues so hopefully they will eventually resolve them.

The antenna on the approximately 4 feet of RG-58 is just a 1/4 wave dipole antenna which is formed by pulling the center coax lead through the braid. Remove 6 1/2" of the jacket and pull the center insulated coax through and form the center and the shield into a "T" shape. I mounted it on a thin plastic sheet and attached the coax with nylon ties. I fabricated some hanger brackets and hung it about an inch below the receiver hitch. This way you have effectively just moved the antenna from it's original hidden location behind the license plate to a location below the RF shielding of metal at the rear of the truck.

Guilty as charged Tbully. I just hope this helps someone else as I have been fighting this since March off and on. Now if the virus would just go away so we can go camping with the 5th wheel.

For Firstascent or anyone else that has trouble getting the truck to read all the sensors reliably. I have been fighting this as well. The stem size problem was resolved by sending them to a guy in Az. that changed them to the .625 with the same sensors. And on the 100 lb. limit. The sensors will read 102 lbs. if you set it to 100, my tires run at 110 lbs. so like someone else said at least I will know when they get below 100. But the system reading the sensors reliably is a real problem. I actually traded from a 2019 to the 2020 for this feature so I didn't need a separate TPMS, along with the camera's, 10 speed transmission etc. I saw on another forum that someone had removed the rear license plate with some success. Sure enough mine all read when I removed it. I opened a ticket with GM and they say it is an engineering issue and closed the ticket. So here is what I did to resolve it at least temporarily until GM comes up with a fix. Problem is lack of signal to the TPMS ECU located on a plastic bracket behind the rear license plate which is blocking the RF signal at 433.920 Mhz. GM part number for this unit is 84458180, I bought one from Ebay for $58 and modified it, removing the small wire antenna which is inside the 84458180 and adding an external dipole antenna crudely fashioned from some RG-58 cable. I mounted the antenna horizontally just below the square receiver hitch and it seems to work on my test run. One thing of note that I failed to realize on my first test run is that the tire sensor information is stored inside the ECU under the license plate. When you replace it you must relearn the sensors. Don't attempt this unless you have adequate bench equipment such as a Hakko solder removal tool or at least a Solder Sucker to remove the solder connections inside the ECU as the pins are molded into the plastic. The shield of the cable was attached to the small square and the plastic inside the cover was reshaped so I could temporarily move the original antenna connection and go back to OEM if necessary.