Ultimate OBD JScan Thread

[Hunoval]

Q re: JSCAN & Bigger Tires: TCU / Shift Point Adjustments. Newbie here. Have been using the OBDLink MX+ bluetooth scanner with the bypass cable in my 2022 Ram Rebel 1500 ecodiesel & the native OBDLink app for about a year-- the driver for choosing the MX+ was / is it appears the fastest in communicating real-time data. Only have iOS devices, and don't want to buy a separate burner Android for the sole purpose of using the AlphaOBD app. Recently changed out tires from the Rebel's OEM 275/70r/18s Duratracs to a 285/75/18 KO3. I don't much care about recalibration for speedo / odometer reasons (running Waze on the OEM 12" provides the actual speed via its embedded GPS) & even if I don't have Waze or a GPS-based speed app running, the math is pretty straightforward to do in your head re: what your actual speed is vs. what the speedo says. HOWEVER, with my now-heavier & taller tires, the transmission shift points are 'off' and it should probably hold gears just a tad longer for smoother driving & to mitigate the now-increased lugging tendencies. I've been thru this entire thread and, while awesome re: JSCAN appearing to be catching up to AlphaOBD.... can't seem to find detailed instructions for recalibration of the TCU / adjusting of shift points for larger tires. I saw some mention that one can do this with JSCAN, but haven't found much detail or a color-by-numbers video on how to do this with JSCAN. Again, I'm a noob & haven't yet installed the JSCAN app so apologies in advance for the no-doubt already-existing thread treating this exact Q. But as you appear to be the resident expert on all matters 5th Gen Ram & JSCAN, TIA for pointing me to such already-existing thread and/or YouTube video going thru the reprogramming of the TCU / shift point adjustment for larger tires. TIA, kind sir!

K. And I assume if I did NOT change the tire size configuration within JSCAN, by disconnecting the battery for 30 mins or so & then re-connecting to reset to factory settings... so ONLY unplugging battery & nothing else, it would 're-learn' shift points even WITH the larger tires?

 

[Jimmy07]

K. And I assume if I did NOT change the tire size configuration within JSCAN, by disconnecting the battery for 30 mins or so & then re-connecting to reset to factory settings... so ONLY unplugging battery & nothing else, it would 're-learn' shift points even WITH the larger tires?

Disconnecting the battery doesn’t do anything. Your shift points are off because the tires are bigger than what the bcm thinks they are, so the size needs to be corrected, which in turn will correct the speedometer and shift points.

 

[Hunoval]

10-4. I thought there was a separate procedure in JSCAN, separate and apart from just resetting the tire size. Tho, as a noob... will defer to those on here with far greater knowledge!

 

[gskowronek]

10-4. I thought there was a separate procedure in JSCAN, separate and apart from just resetting the tire size. Tho, as a noob... will defer to those on here with far greater knowledge!

Let me know how it worked, I'm about to change my OEM 285/45/22 to 295/50/22

 

[drpepper68]

Mine was already set to accommodate my 37in tires after looking in jscan but speedometer is still off by 4mph.

 

[wickedmopar]

When I went to 35's from OEM I was off by 4mph, verified on Waze at several different speeds. Updated in JSCAN and now it's spot on. I did manually measure tire rather than go with what it said online, they were different values. I chose to use the value on the front tires.

@drpepper68 did you manually measure your tire as advised in JSCAN?

 

[mplaramie]

Anyone know how to back up current factory settings with Jscan before making changes? Just want to make sure if I screw something up, I can go back to the point before the f-up.

 

[theblet]

Anyone know how to back up current factory settings with Jscan before making changes? Just want to make sure if I screw something up, I can go back to the point before the f-up.

I believe the JSCAN logs show you every change you make, and you can roll the changes back within the app.

 

[Brutal_HO]

Anyone know how to back up current factory settings with Jscan before making changes? Just want to make sure if I screw something up, I can go back to the point before the f-up.

Connect to your truck then tap the gear icon on the top right, from that menu go to "Trace & Restore Adaptations"