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Speedometer Calibration

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25
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12
Location
Salina
#1
For everyone that has changed tire sizes on their FiST: did you just learn to live with the speedometer being off? I've switched to a 205/50R16, changed the rolling diameter with FORScan to the largest option, and my speedometer is still slow by about 2.6%. I know that doesn't sound like much, but it's driving me insane. I tried changing the actual "tire size" option in FORScan as well to no avail. To be honest, the speedometer I can live with, but the odometer bothers me more. I tried to make a HEX edit to the rolling diameter line in the IPC ASBUILT data, and ended up bricking my IPC and had to jump power to it to flash it again.

I feel like making the change in FORScan didn't do anything because my speedometer is off by basically the exact same amount as my tires are larger than the factory 205/40R17.

The Fusion and F-150 forums have TONS of FORScan related info, but the Fiesta seems to be programmed differently than them. They are able to edit a line in the BCM to any arbitrary number to edit their rolling diameter.

Thanks for any insight anyone may have.
 


OP
Dahveed
Messages
25
Likes
12
Location
Salina
Thread Starter #2
Follow up! This evening I ran the PCM relearn function in FORScan and my speedometer is dead on now! So if it was any question before with the Fiesta even without the P160A code the PCM does not learn the rolling diameter or tire size you have entered until you run the PCM relearn.

I put the dashboard in test mode so I could see the digital speedometer, set the cruise on 75, and timed myself through several miles of mile markers and averaged 74.4mph with the cruise fighting a headwind and 75.3 mph with the wind at my back.

GPS agreed with these speeds as well. I'm so happy I could scream!
 


mrmrva

New Member
Messages
1
Likes
0
Location
Serbia
#3
Hey @Dahveed what year is/was your Fiesta? Can you check my screenshot and let me know which option did you use for PCM?
 


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