Recently I purchased an MPT tune and after installing it I noticed the speedometer was off as follows (speedometer/gps) 20/21-22 40/42-43 60/64-65. This was monitored using GPS from several different devices and different apps. I don't believe the issue to be the tune that's just when the issue started. I have imput the correct revs per mile and rear-end gearing into the tune. I have also put the wrong information in the tune to check and nothing changes. I have been back and forth with MPT for a month now and probably 8 tune revisions and that has not solved the issue either. I have returned the vehicle back to stock and the speed is still off. I've done everything I can think of though I haven't disconnected the battery and reconnected it so maybe I'll try that and see if it resets anything. Does anyone have any input or direction I can go in to try and fix this issue? All the software and firmware is up to date. I'm using a sct bdx tuner.

 

So no matter what changes you make to tire size it never changes via the tuner?

have you tried changing tire size in forscan?

 

No matter what I input the speed is off the same amount. Even when MPT did the tune revisions and they input everything and made it where I can't adjust anything it's still off the same amount. I dont have forscan? I've done everything I can through the bdx tuner.

 

Yeah, not sure. I’ve seen people have issues adjusting using the tuner with error codes and such.

I would try forscan, it’s free minus the cord.

 

I'll look into getting one. I haven't have any issues using the tuner to make changes until I loaded the most recent tune. I've been using it for 3 years no issue.