You will need to take it to a parts store like NAPA and see if they will read the tcm (transmission control module) for codes, if all else fails then take it to a transmission shop and ask if they can scan it for codes and check the functionality of the tow haul button if it is not functioning, it could be just a broken wire from flexing at the base of the shifter.
Answers & Comments
You will need to take it to a parts store like NAPA and see if they will read the tcm (transmission control module) for codes, if all else fails then take it to a transmission shop and ask if they can scan it for codes and check the functionality of the tow haul button if it is not functioning, it could be just a broken wire from flexing at the base of the shifter.