0216HD

2016 2500HD has been telling me to service the trailer brake since new. Dealer attempted many times under warranty but never succeeded. Sometimes it works, sometimes not. Sometimes after connecting a trailer a shut down and restart will bring it online but not always. Notice comes on with every startup with or without a trailer connected. After I gave up with dealer I personally have replaced the circuit board in dash and the module above the spare tire. Resistance tested all the connections I could find and searched for chafed / broken wires. I've had countless conversations with GM. Best they have ever did was offer me a $100 coupon to get my truck serviced at dealership. I'd be interested to hear from anyone with a working background of the problem that might offer some suggestions as to where to look next.