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15 lml 133k just recently noticed my tow haul is not working. When i press it the light DOES come on the dash but nothing changes driving wise. Couple weeks ago i had to replace my tcm due to it dieing while flashing a tune through ezlynk that had tcm tuning on it. I got a tcm with the factory calibration sent to me from a reputable vendor. (Im still waiting to here back from them.) I also went with new efilive tuning so i'm not sure if that has something to do with it (seems unlikely to me). My question is do you think the wire that is known to chafe on older trucks could be bad? I find it hard to believe seeing the truck shows the trailer dummy light on the dash when i turn tow haul on. I did some research but couldnt find anyone that had tow haul failure with the dummy light still working. Any insight is appreciated, i wanted to check here before i started pulling my steering column apart.
 

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15 lml 133k just recently noticed my tow haul is not working. When i press it the light DOES come on the dash but nothing changes driving wise. Couple weeks ago i had to replace my tcm due to it dieing while flashing a tune through ezlynk that had tcm tuning on it. I got a tcm with the factory calibration sent to me from a reputable vendor. (Im still waiting to here back from them.) I also went with new efilive tuning so i'm not sure if that has something to do with it (seems unlikely to me). My question is do you think the wire that is known to chafe on older trucks could be bad? I find it hard to believe seeing the truck shows the trailer dummy light on the dash when i turn tow haul on. I did some research but couldnt find anyone that had tow haul failure with the dummy light still working. Any insight is appreciated, i wanted to check here before i started pulling my steering column apart.


i would say that if the light on the dash is showing a change of state that corresponds to pressing the tow haul button that the wiring of the button is not the issue.

Just to rule out the the simple stuff, did you do the transmission relearn after replacing the TCM in both tow haul and regular mode? tow haul mode has separate settings from standard driving so if you have not used tow mode it may need to learn before it shifts properly.
 

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I drove accordingly to re learn the trans how ever i did not do so in tow haul mode thats pretty much what i was going to do yesterday and thats when i noticed it not working. My truck in regular driving mode seems fully re learned. It border line seems like the company who supplied my tcm only loaded the shift strategies for regular driving and nothing for tow haul. I could be completely wrong on that assumption but thats the only thing i can come up with.
 

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Did you ever fix this issue? I'm having the same issue on my 2011. The dash light will come on when I press the button, but the TC will not lock. So far it has always eventually started working after driving it for about 5 miles. None of the following helps: repeatedly pushing the button, tuning on t/h before starting, reversing first then forward, turning it on while moving.
 

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Did you ever fix this issue? I'm having the same issue on my 2011. The dash light will come on when I press the button, but the TC will not lock. So far it has always eventually started working after driving it for about 5 miles. None of the following helps: repeatedly pushing the button, tuning on t/h before starting, reversing first then forward, turning it on while moving.
What gear and speed are you in /going when you expect the converter to be locked but it is not? My understanding is that even in tow haul mode the converter will not lock below 3rd gear. Also what are you using to monitor the state of the converter lockup?
 

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What gear and speed are you in /going when you expect the converter to be locked but it is not? My understanding is that even in tow haul mode the converter will not lock below 3rd gear. Also what are you using to monitor the state of the converter lockup?
I have an edge cts to monitor which gear I'm in and if the TC is locked. Back when t/h was working it would lock the tc in second gear and up. It shifts 1 to 2 and then at certain speed locks in 2 then goes to the rest of the gears and locks them immediately.
 

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I was hoping to avoid going to the dealership, but I am towing this weekend and didn't want to chance it. I took it in earlier today. I should know tomorrow. I'll let you know what they find.
 

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The dealership scanned the truck and said tow/haul is working correctly and then charged me $150. I KNOW it is not working correctly. I have towed with this truck for 4 years. I have a edge display that tells me when the tc is locked and what gear I’m in. So frustrating.
 

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Maybe it was you tcm tuning that was locking it when in 2nd with it in tow/haul.
 
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