VIN: 3D7KA28634G130923. If you have a way to attach a file, I have a pdf of the Dealer Options Report on the truck. If I understand it correctly, it has the maximum tow package available for the year. That's why we bought it.
Just ran a code check on it. Came up with a P0633 Generic. Immobolizer Key Not Programmed - ECM/PCM. No check engine light. Google search suggests that the PCM was replaced and the proper programming not done. We did have to replace the PCM last year. Couldn't afford the dealer markup, so bought one online, sent them the VIN for programming, and have had no problems since. Articles suggest that this could result in a no-start condition, so at least we know the possibility exists and what to do about it. I will clear the code and see if it re-sets.
Back to the issue at hand... I have two distinct symptoms. First, after a long climb in the tow/haul mode, coming down the back side of the hill and still in tow/haul mode, the tranny will sometimes drop out of gear entirely. Once at the bottom of the hill, putting power back on seems to resolve the issue and the system runs normally. We tow several times per year and experience this symptom only occasionally. The truck is rated to tow just over 13,000 lbs but the hitch system factory installed is only rated at 10,000lbs. Our trailer is 9600GVW but I estimate our tow weight btw 7k and 8k.
Second symptom has happened only once, on our last trip. After a*****up highway 101 in northern California, after the last hard climb, coming down the back side of the hill, the entire tow/haul function disappeared... no indicator light on the dash, no downshift out of overdrive... no response at all. I had to use my brakes
alone instead of in conjunction with the engine/tranny helping to hold back. We got home with the tranny in normal mode, seemingly shifting normally, but again, could not get a response from the tow/haul mode. Parked the trailer and unhitched. About 3 hours later, took the truck to a friends house. Tow/haul mode had returned and seemed to operate normally and has since (about 4 weeks), though with no towing involved. We'll be taking the trailer out again in the morning (Friday, Aug 11) for a trip down highway 101 again to Santa Rosa and back on Saturday. Will be interested in seeing if the symptoms and code return.
There has been no check engine light since before we replaced the PCM and the IPM about 7-8 months ago. Will be happy to report back if the system lets me. Any other questions, please let me know.
Thanks again... Jim Norton