Forscan tire size wiped out after recall update?

[AZ_Ryan]

I had my tire size updated by a dealer using Forscan to match the new HP tires shortly after I bought it (car was originally a non-HP). The speedo was never perfect after that, but it was much closer. Within about 2 miles or so at freeway speeds after the update. Today I noticed my GPS is off by around 5 miles at freeway speed again, same as it was before the update.

Only thing I can think of is the recall update for the brake fluid indicator light wiped out the previous tire size programing. Has this happened to anyone else?

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[Lucky13Cat]

My dealer said he couldn’t do anything with my speedometer with forscan.

 

[Hoose71]

I had my tire size updated by a dealer using Forscan to match the new HP tires shortly after I bought it (car was originally a non-HP). The speedo was never perfect after that, but it was much closer. Within about 2 miles or so at freeway speeds after the update. Today I noticed my GPS is off by around 5 miles at freeway speed again, same as it was before the update.

Only thing I can think of is the recall update for the brake fluid indicator light wiped out the previous tire size programing. Has this happened to anyone else?

I was wondering if that might happen. I'm going to check my settings before and after I get the update. I made the changes myself, so I can always switch it back. Here are instructions I put together for someone on Facebook:

Just for reference, for 315/30’s the new speed reference is 2,047 on HP rims.

Under configuration and programming there are two modules you will be modifying, both BdyCM modules.

Under BdyCM you just enter the tire circumference that you are changing to (2047 for 315/30's) This is the easy one.

Then using an online calulator, enter the same circumference to find the HEX value. In this case 2047 = 7FF (or 07FF)

Now in the BdyCM (Asbuilt Format) you need to go down to 726-15-01 and 726-15-02. This is where you enter the Hex values to match what you put into the other module. Before modifying anything, save the existing configuration. This way you always have a backup that you can restore if anything goes wrong. You can also confirm you have the right locations by checking the original circumference value in BdyCM and confirming it's hex value in BdyCM (Asbuilt) matches.

After cycling power on the car you may need to reset the module, under service functions. Possibly reset some DTC's as well. But the speedometer should be much more accurate now.

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