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theksmith

how to calibrate speedometer (change tire size) on 2021 Jeep Grand Cherokee WK2 using AlfaOBD

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Required:

  1. The Alfa OBD app ($50) for Android
  2. An OBD2 BT adapter: OBDLink LX ($60) is a high-quality supported product, or iCar Pro BLE is super cheap and seems to work for most things.
  3. 2018 and newer vehicles also need a bypass dongle or a 12+8 cable ($30) to get around the FCA Secure Gateway Module (SGM).

 

On the 2018+ WK2's, the SGM module you need to bypass is under the dash on the passenger side (below the glove box). You need to pop the felt cover that's under there off (2 push-pin fasteners). The SGM is up against the transmission tunnel area.

 

I used the 12+8 cable method to get around the SGM.

 

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I'm only going to document an overview of the steps involved and may not spell out every single click in the app. For the basics on how the app works, check out the help file on the AlfaOBD website, this WK2 specific thread about AlfaOBD, and possibly the AlfaOBD "bible thread" on RamForum.com. 

 

 

Important! Backup your existing BCM config first:
 

It's important to have a backup of your BCM's original config as a reference in case you or the app screws something up!

 

  1. Jeep "ON" but not running.
  2. Connect to the "Body Computer".
  3. Note: Under "Control Unit", if your exact year of WK2 isn't shown, then select the newest one that is less than your year.
  4. Go to the System Status screen (Battery icon at bottom)
  5. Click on the Read System ID button and wait till the box below stops filling with info (keep scrolling down).
  6. Click on the Read System Status button and wait again till the box below stops filling with info (keep scrolling down).
  7. Go to the Tools screen (Wrenches icon at top)
  8. Click the Google Sign-In button and allow AlfaOBD to access your Google Drive
  9. Click the "Upload Faults and Status Log" button and select "Body_Chrysler_Info" if asked for which file, then wait till there is a popup msg at the bottom that the file was uploaded.
  10. Go to your Google Drive using the Drive app or website and find the "Body_Chrysler_Info.log" file. Open it and verify it has 20+ pages of text.

 

 

Adjust speedometer/tire-size:

 

  • New tire size:
  1. Be sure the Jeep is "ON" but not running and you're connected to "Body Computer" still (see steps above).
  2. Go to the "Active Diagnostics" screen (Hood up icon at bottom)
  3. Procedure = "Car Configuration Change" (near bottom of list)
  4. Option = "VehConfig 4: Dynamic Tire Circumference (All or Rear) (0-65534mm)"
  5. Note: Alternatively you could just do Procedure = "Program Tire Size" and select from a list of tires/sizes, but this may not get you precise results.
  6. Value = (your new tire circumference in MM (calculator here...)
  7. Note: My original value was 2371.000 (29.7" tire) and my speedo was slow by 2-3 MPH at 75. I ended up with 2430.000 (30.45" tire) - even though my tires are actually 31.5" (265/65R18), but with that value the speedo was dead-on with the GPS at 75 MPH.
  8. Press the "Start" button in the app and wait a few seconds.

 

  • Reset ABS:
  1. Before starting, be sure you are on level ground with the brake pedal and parking brake NOT pressed!
  2. Without turning off the Jeep, change the app connection to "ABS", Control Unit = (the one with "Teves" and "My2014+ PowerNet")
  3. Then go back to the "Active Diagnostics" screen (Hood up icon at bottom)
  4. Procedure = "ABS Initialization"
  5. Press the "Start" button in the app.
  6. Change to Procedure = " Static ECU Initialization"
  7. Press the "Start" button in the app, then "Next", then wait a few seconds.
  8. Change to Procedure = "Longitudinal acceleration sensor calibration" (must be level with no brakes pressed during this!)
  9. Press the "Start" button in the app, then "Next", then wait a few seconds.
  10. Change to Procedure = "Clearing Rolls information"
  11. Press the "Start" button in the app, then "Next", then wait a few seconds.
  12. Go to the "Faults" screen (Check engine light icon at bottom)
  13. Press the "Read All Faults" button, then clear any faults that are listed

 

  • Verify & possibly clear extra faults:
  1. Turn the Jeep off completely for 30 seconds, then start the vehicle.
  2. Verify no new warning show up in the cluster. If there are problems, see below about resetting faults in other modules.
  3. Use a speedometer or GPS app on your phone to verify your speedo. Repeat the whole procedure again if you need to adjust more.

 

 

Possible problems/warnings:

 

When I first tried to accomplish this using the slightly different procedure listed on the RAM Forum, I got a warning in the cluster saying "Park Sense Not Available" after re-starting the Jeep. I ended up having connect to the "Parking" module and use the Clear Faults feature to clear a code in there, then without turning off the Jeep, repeat the entire procedure above.

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It's worth noting that the OBD JScan app now claims to be able to adjust tire size as well: http://jscan.net/jeep-grand-cherokee-wk2-lift/

 

OBDJScan is cheaper, but you license it per vehicle ($15) whereas AlfaOBD is a one time cost ($50) for use on unlimited vehicles.

 

JScan also appears to have an iOS version whereas Alfa is only available for Android and Windows.

 

I used JScan on my JK and it was a much simpler process, but I've not tried it with the WK2. Please post a reply if anyone has successfully used it on a Grand Cherokee.

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Thanks very much for the detailed instructions... very helpful!

 

I can confirm that tire size adjustment using JScan iOS worked for my 2020 WK2.  I had some problems with an earlier version (8.0), but everything seemed to work correctly after I upgraded to the latest (10.0).

 

As documented above (I also have 265/65R18 tires), I chose 30.5" tire height (2337 mm circumference), and the speedometer is right on at 75 MPH. After making that change, I had to reset the ABS module to clear the ABS warning light.

 

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7 hours ago, markGH said:

Thanks very much for the detailed instructions... very helpful!

 

I can confirm that tire size adjustment using JScan iOS worked for my 2020 WK2.  I had some problems with an earlier version (8.0), but everything seemed to work correctly after I upgraded to the latest (10.0).

 

As documented above (I also have 265/65R18 tires), I chose 30.5" tire height (2337 mm circumference), and the speedometer is right on at 75 MPH. After making that change, I had to reset the ABS module to clear the ABS warning light.

 

 

thanks for confirming about JScan!

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Nice write up as always Kris.

 

Question:  Will the Alf OBD App. Program aftermarket key fobs?

 

 I asking specifically about a 2017 RAM and I’m computer illiterate. 😜

 

 

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13 hours ago, jgaz said:

Nice write up as always Kris.

 

Question:  Will the Alf OBD App. Program aftermarket key fobs?

 

 I asking specifically about a 2017 RAM and I’m computer illiterate. 😜

 

 

 

yes, my understanding is you need yet another app first to pull a special code that normally only the dealer can pull. i'll see if i can find the info for you...

 

 

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Posted (edited)
12 minutes ago, theksmith said:

 

yes, my understanding is you need yet another app first to pull a special code that normally only the dealer can pull. i'll see if i can find the info for you...

 

 

 

 

found it - though i haven't tried it myself yet, it is on my todo list.

 

first use this app to pull your "key programming pin code", i think you can do it once for free, then have to pay for additional times: Chrysler Pin Puller

 

then, this post on RAM Forum walks you through the AlfaOBD procedure.

Edited by theksmith

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Thank you so much Kris for looking into this!  I’m up at the canyon and am just now able to get online.

 

I have two (I think) code numbers that I asked politely (forced) the dealer to give me before I would take delivery of my truck.

One number I’m sure is correct.   I used it to have a  couple conventional keys  cut to use in case of a lock out.

 

I will look into pulling my Programing  PIN and compare it to what I already have.  It must be worth something because getting the dealer to give the numbers to me was like pulling teeth.

 

Thanks for the RAM forum link I’ll check it out.

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Sorry to pull up an old thread, I signed up just for this.

 

Kris - in AlfaOBD, were you actually able to press the START button under ABS Initialization, or did you go straight to Static ECU Initialization? I reached out to the developer but haven't heard anything.

 

Thanks for the great write-up!

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1 hour ago, mikenigrelli said:

Sorry to pull up an old thread, I signed up just for this.

 

Kris - in AlfaOBD, were you actually able to press the START button under ABS Initialization, or did you go straight to Static ECU Initialization? I reached out to the developer but haven't heard anything.

 

Thanks for the great write-up!

 

i think so, but can't say for certain now, it's been so long

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