Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
If there have been three years of trouble-free towing up to this point and no modifications have been made lately, then the symptoms you describe are probably being caused by open circuit(s) between the trailer and the truck. If I were you, I'd start by taking a close look at both halves of the trailer connector. If both show no signs of corrosion or debris and there aren't any broken wires, then get a spare battery and start running voltage drop tests on the trailer circuits until the culprit is found.
Please let me know what you find.
99.99% of the cases, additional circuit resistance is what causes this type of fault - GM even came up with TSB 09-05-22-004 to address this issue by reprograming the ITCBM with an updated calibration. In a case like this, where the system was OK one moment and bad the next, I couldn't think of anything other than excessive circuit resistance that could cause this issue.
Please let me know if there is anything else I can do to help.
By the way, I'm curious. You used the acronym "SSR", which I could not find in the GM glossary other than when used in reference to the little truck they no longer make. What does it mean?
The only way we would be able to see what's going on is by establishing communication with the DIC and the ITBCM through the bus network. Can your scan tool get on the serial data bus? Can it communicate with those two modules?
OK. If I understand you correctly, the TCBM is showing trailer and brakes connected even though those are in fact disconnected. Is that so? Then, DIC is not showing trailer and brakes connected whether those are connected or not. Is that correct?
Regarding the DIC, there are two instrument panel cluster (IPC) options for these trucks; one with and one without Driver Information Center (DIC).
The only way we're going to be able to solve this puzzle is with the help of a Tech-II or equivalent scan tool that can communicate with all of these modules.
OK. Now I'm really confused; first you posted "No codes, no trailer recognition on DIC", now you post "IP has no DIC". What are we trying to do here?
Now you're confusing me even more; what do you mean by "Information I have says trailer info shows up on IP display". What information are you talking about? Are you not there with the truck? Can't you just look at it and see if it has a DIC? If you need to, click here to look at a video on how the DIC works.
OK. I did some digging of my own and this is what I came up with: if it has OEM trailer brakes system, then it has a control panel on the left lower side of the dash. Also, the trailer brakes system will communicate with DIC and show when trailer is connected and disconnected plus rate of brake application.
Now, here is the important part; if the total resistance of the circuit for the electric brakes on the trailer exceeds 3.0 Ohms, the DIC won't show the trailer brakes at all.
Hope that helps, brother. If not, I don't know what else to do that can help you fix this thing.
Click here for instructions on how to test SSR
OK. Before we get confused again, what are we trying to fix; the trailer electric brakes, or why they don't show up on the DIC?
On second thought, the more I learn about the system, the more I see the need for a Tech-II or equivalent scan tool as the only tool that will allow us to conduct an effective diagnosis. Since it seems you don't have access to one of those (Modis doesn't have serial data communication capability), I'll opt out so others may try to help you. Please don not reply until another expert responds or the site will cycle your request back to me.