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You're saying it reads correctly right now, and you'd like to mess it up to read slower? Does your wife have a lead foot ? I would hope you only want to change it to read less than 5mph off (at ~65mph), otherwise you'll be artificially lowering the resale value by ticking off more miles on the odometer than are actually traveled.

Two options:
1) Put on smaller diameter tires
2) Re-program the speedometer forlarger diameter tires, w/o actually changing them. I'm not sure how to do this step, may need the dealer to do it. In the old days, youhad to change the speedo gears in the tranny, but these days, I think you can re-program something.

 

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the tuning software is for the PCM engine computer not the tranny computer which the output speed sensor is getting the infor from. Plus u know if u do what u are wanting to do u will be braking the fed law?? It will show lower milage that what is really on the van and if some one was to check it out the other computers will not show the same info as the one u change.

 

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Actually, if he makes the changes the way he wants to (speedo reads faster than actual speed), he'll be doing the opposite - ticking off more miles on the odometer than were actually travelled.

 

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Why in such a hurry? You said this was just for experimentation. This isn't a routine that's performed by lots of people I don't think, so you're gonna have to wait for CHRYSLER_TECH or someone else to respond. This thread has actually recieved MUCH quicker responses than most threads on this forum.

 

ok here is the deal if u change the ratio in the the computer which if u had bigger wheels so u say then u would change the ratio if u can some will some wont Jeeps allow this on most because it is offered with different wheels from the factory. The change will be done in the ABS module which uses the wheel speed sensors for the rpm of the wheels. If u change the ratio to as close to what size tires u have on there now then it will change the mph on the speedo for u. The speedo info is done via BUS so the speed is networked over the bus from which ever computer is controling it for that year. If all u want is to change the ratio then go ahead but it will haft to be done at the dealer unless there is an aftermarket shop that has one of the real high end scanners that can get into the ABS module and they might be able to change it i dont know aftermarket scanners.
But i do know a chrysler dealer can if that year ABS module allows changes.