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I just recently changed my tires to Toyo M920's that are 245/70R19.5 which is an increase from the stock 225/70R19.5's. My speedometer is now about 3.5% low compared to GPS speed. I have downloaded ForScan and have a bluetooth OBD2 module. I have never used forscan yet, but most of it seems pretty easy, except changing the tire size. The Forscan spread sheer says current value will be: xxxx xx00 xxxx and new value will be: xxxx xx4C xxxx. It also says that the following can be used and not get a check engine light: xxxx-0AAE-xxxx
So what value exactly do I enter for my tire size?
Using this calculator, here's a screenshot showing the value and the FORScan line for your tire size. The link will take you to the complete calculator with other steps and instructions, including inputting your speedo reading and the GPS reading to come up with a FORScan value.
I just noticed that I put your stock tire size in, not your current tire size. But you can change that to get the correct value. My apologies.
Has the guidance on CELs occurring with this method changed Does this method work for tires outside factory range (like 36.6”)?
Can't help you out there. I only went to a 325/65R18 which puts me at 34.6 inches, compared to the stock 275/65R18 at 32.1 inch. I never had a CEL.
Did you check out the link and try step 3 on that chart?
Using this calculator, here's a screenshot showing the value and the FORScan line for your tire size. The link will take you to the complete calculator with other steps and instructions, including inputting your speedo reading and the GPS reading to come up with a FORScan value.
I just noticed that I put your stock tire size in, not your current tire size. But you can change that to get the correct value. My apologies.
Can't help you out there. I only went to a 325/65R18 which puts me at 34.6 inches, compared to the stock 275/65R18 at 32.1 inch. I never had a CEL.
Did you check out the link and try step 3 on that chart?
I have the same size tire. Did you use 0A70 on your truck? Did you have to do the relearn process shown in Step 3? Thanks!
I have the same size tire. Did you use 0A70 on your truck? Did you have to do the relearn process shown in Step 3? Thanks!
Even if you don't get a CEL, running the FORScan PCM relearn routine clears the P160A DTC that you will get after changing tire size. In theaory, the P160A DTC shows up because of the different PCM & TCM wheel size values, since we only change the values in the PCM.
Even if you don't get a CEL, running the FORScan PCM relearn routine clears the P160A DTC that you will get after changing tire size. In theaory, the P160A DTC shows up because of the different PCM & TCM wheel size values, since we only change the values in the PCM.
can you change it in both PCM and TCM to avoid the relearn?
I have the same size tire. Did you use 0A70 on your truck? Did you have to do the relearn process shown in Step 3? Thanks!
I really can't recall, it's been well over a year for the tires and about a year since I last used FORScan for changing all the bulbs in the truck over to LED. But I just plugged the tire size into the calculator and got the 0A70 value so I'm betting that I probably did. I never had a CEL so I don't remember whether I did the relearn or not. Sorry I couldn't be of more help.
can you change it in both PCM and TCM to avoid the relearn?
I believe you cant change TCM parameters with FORScan. Following the 3 steps oulined above will get you an accurate odometer & speedometer reading without any CEL or DTCs
I just tried the change mentioned above 09AC to 0A70, then did the relearn and I got the following error: P1635 - Tire/Axle Out of Acceptable Range. I am curious if anyone else got that message and how it was resolved. I wonder if this is because I have the 6.7 and 3.31 axle ratio. Perhaps others that have used 0A70 have the 3.51 axle ratio and that is within spec for that axle. Oh well, changed the value back to orifinal and the CEL went away. Save this project for another day.
I just tried the change mentioned above 09AC to 0A70, then did the relearn and I got the following error: P1635 - Tire/Axle Out of Acceptable Range. I am curious if anyone else got that message and how it was resolved. I wonder if this is because I have the 6.7 and 3.31 axle ratio. Perhaps others that have used 0A70 have the 3.51 axle ratio and that is within spec for that axle. Oh well, changed the value back to orifinal and the CEL went away. Save this project for another day.
I have a 6.7 with 3.55. i got a similar error when i tried to make the numbers for 37 work. Still running stock values until someone can help figure it out
Not even worth it. Its Ford's problem - I get 7.8% more warranty the way it is now. LOL I wish I could find out what the acceptable range is so that I could at least get the speedo close though.
