Pre-collision assist & cruise control problem

[Ken H.]

I’m sorry if I’m over-posting or posting in the wrong place but i could really use some input. I posted in another location earlier today & got no response. Have meeting with dealer today.
Error message that pre-collision assist & adaptive cruise control not available. Can’t switch to normal cruise control. Dealer could not reset. Ordered/replaced Cruise Control Module. Still unable to reset. Dealer consulted with Ford & they’re telling me that it’s the new wheels/tires causing problem & I have to put original set back on. New set put on in March 2025 at 900 miles. Now 5,000 miles. Problem started 2-3 weeks ago.
DH HP 305/30/19 front & 315/30/19 rear stock
Now 285/35/20 front & 305/35/20 rear.
Doesn’t make sense to me. Why would it take 3 months of daily driving & road trips for the computer to detect a problem with the wheels? Any advice?

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[Skye]

https://www.mustang6g.com/forums/th...-available-message.175415/page-2#post-4251298

I do not have an answer for you, but maybe a few suggestions.

While I have a different Model Year, in April I had a similar experience. It's happened once, then cleared after a brief pause. It has not re-occurred.

In the thread above, while some vehicles are tuned, mine is not. Something common seems to be the clearing of a logical fault in the car (my interpretation). My fault cleared by itself. To others, theirs cleared after reloading their tune.

Suggestions...

1. Disconnect the battery and let the vehicle sit for several hours, if not overnight.

2. Even though it is not giving you any indications, ask the dealer to re-flash the Body Control Module. The activity should reset any sensors or modules in the process. Basically, you're rebooting the car.

I can appreciate the dealer's notion the wheels and tires are at fault. But if that was the case, it should be happening to any vehicle much more frequently. And in your example, much sooner. Further, I'd think they could clear the fault with the vehicle stationary, with the events repeating after a short drive?

As a reference, the circumference of my aftermarket tires is within 3% of the factory. They work fine. In extreme examples, the limits of which would be different for different vehicles and years, the diameter of the tire can cause speedo, cruise, ABS and shift points to work less than optimum, but they continue to work.

If the dealer insists, if possible, move back to the factory wheels and tires. It's not the preferred route, but if the only way ahead...another option: consult another dealer.

 

[Skye]

I'm attaching some screenshots, comparisons of your before/after tire and rim selections.

While I do not know what the limit is, the circumferences of your tires are more out than I'd be comfortable with.

In my example, I'm within 3%. In yours, you're more than double out. This gives weight to the Dealer wanting to put the car back to baseline before going further.

I cannot explain the delay in logic, why the car is struggling now. And the tire size difference might not be the issue. But we do not have data to say otherwise.

Hopefully, someone with a similar change will see this thread and offer feedback. Unfortunately, I suspect the Dealer will continue to want to operate with a known baseline, before proceeding.

 

[Zig]

I'm attaching some screenshots, comparisons of your before/after tire and rim selections.

While I do not know what the limit is, the circumferences of your tires are more out than I'd be comfortable with.

A general rule to follow is to keep the circumference of the new set within 3% of factory. Otherwise, speedo, shift points, ABS, etc., can change, sometimes, not for the better. The vehicle is programmed for one thing, while the Owner has effectively changed the gearing to something else.

In my example, I'm within 3%. In yours, you're more than double out. This gives weight to the Dealer wanting to put the car back to baseline before going further.

I cannot explain the delay in logic, why the car is struggling now. And the tire size difference might not be the issue. But we do not have data to say otherwise. We know what the factory programmed the car for, not what the limits of the sensors and logic are.

People can and do exceed limits all the time. Without issue. Maybe yours is a problem. Maybe not.

Hopefully, someone with a similar change will see this thread and offer feedback. Unfortunately, I suspect the Dealer will continue to want to operate with a known baseline, before proceeding.

But why does the system need to know how quickly when obstacle detection is the intent? As in rolling distance is being used to determine proximity of obstruction? While i agree putting the original wheels back on to assist resolution i’d be fearful the cost for repair and resolution would then be assigned to the customer if wheels turn out to be the cause.

radar plus camera plus software minus undetermined ground plus sufficient voltage = electronic flag man.

hopefully, they get you (op) back on the road asap.

 

[Skye]

But why does the system need to know how quickly when obstacle detection is the intent? As in rolling distance is being used to determine proximity of obstruction?

Look at ourselves and how we react to change. If we we're simply guessing or had vision which compromised our judgment, we'd be smashing into things constantly. Changing the wheel size past a certain limit does the same to the computers in the vehicle.

 

[Zig]

Look at ourselves and how we react to change. If we we're simply guessing or had vision which compromised our judgment, we'd be smashing into things constantly. Changing the wheel size past a certain limit does the same to the computers in the vehicle.

But how did the computer determine the calculated distance was wrong and if capable why didn’t it self correct? (Why is a tune needed for tire size changes)

 

[Skye]

But how did the computer determine the calculated distance was wrong and if capable why didn’t it self correct?

Because the vehicle measures the rotating speed of the assemblies (engine RPM, transmission output, ABS collars at the hubs, GPS references, etc., versus what it is programmed for.

Any vehicle sold new is required to meet a factory tested and approved baseline. Ford and other vendors cannot certify (safety, emissions, pricing, etc.) the countless variables involved; they'd bankrupt themselves overnight.

 

[Zig]

Because the vehicle measures the rotating speed of the assemblies (engine RPM, transmission output, ABS collars at the hubs, GPS references, etc., versus what it is programmed for.

Any vehicle sold new is required to meet a factory tested and approved baseline. Ford and other vendors cannot certify (safety, emissions, pricing, etc.) the countless variables involved; they'd bankrupt themselves overnight.

So error detection vs system optimization

 

[Zig]

Because the vehicle measures the rotating speed of the assemblies (engine RPM, transmission output, ABS collars at the hubs, GPS references, etc., versus what it is programmed for.

Any vehicle sold new is required to meet a factory tested and approved baseline. Ford and other vendors cannot certify (safety, emissions, pricing, etc.) the countless variables involved; they'd bankrupt themselves overnight.

Why didn’t the speedometer flash in error?

 

[Junkyard Dog]

I'm attaching some screenshots, comparisons of your before/after tire and rim selections.

While I do not know what the limit is, the circumferences of your tires are more out than I'd be comfortable with.

A general rule to follow is to keep the circumference of the new set within 3% of factory. Otherwise, speedo, shift points, ABS, etc., can change, sometimes, not for the better. The vehicle is programmed for one thing, while the Owner has effectively changed the gearing to something else.

In my example, I'm within 3%. In yours, you're more than double out. This gives weight to the Dealer wanting to put the car back to baseline before going further.

I cannot explain the delay in logic, why the car is struggling now. And the tire size difference might not be the issue. But we do not have data to say otherwise. We know what the factory programmed the car for, not what the limits of the sensors and logic are.

People can and do exceed limits all the time. Without issue. Maybe yours is a problem. Maybe not.

Hopefully, someone with a similar change will see this thread and offer feedback. Unfortunately, I suspect the Dealer will continue to want to operate with a known baseline, before proceeding.

Where can I find this comparator on the internet?

 

[Skye]

Where can I find this comparator on the internet?

https://tiresize.com/comparison/

https://tiresize.com/

 

[Skye]

Why didn’t the speedometer flash in error?

Questions like this are only going to be answered by the Engineers at Ford. They know what the car is programmed for. They know the limits and when the logic begins to fail.

To summarize my previous comments and thoughts: while the wheels/tires are past a % I'm comfortable with, IDK if that is causing these issues or what the limit is. But I've shown they are 6-8% out and the Dealer wants the car back to the Ford baseline before going further.

Best Wishes to the OP and getting this fixed.

 

[Ken H.]

Thanks Skye for the advice & the tire comparison tool. I responded earlier but didn’t hit post. Took wheels to dealer today. Spoke with mechanic. Says there is a “SSM” about it. Pretty sure it’s the new tires being too tall. Says the camera in the windshield has to see the road to gather data for the computer. By having taller tires, thinks camera can’t see road. Also, can’t switch to normal cruise control because if you have adaptive cruise, it uses wheel sensors AND camera data. If no adaptive cruise control, uses only wheel sensor data. That why I can’t just change to normal cruise control cruise control.
If stock setup fixes problem with a repeat calibration, then I will probably get new all season tires for the 20” wheels that match my stock front 19” setup. May not have to change rears.
side note - dealer can’t use Forscan to adjust speedometer for different tires but says Whipple tune can be purchased & it has adjustment tool for tires/speedometer. However, Whipple tune is specific to just one VIN but Forscan can be used on any vehicle.
Learning new stuff.

I'm attaching some screenshots, comparisons of your before/after tire and rim selections.

While I do not know what the limit is, the circumferences of your tires are more out than I'd be comfortable with.

A general rule to follow is to keep the circumference of the new set within 3% of factory. Otherwise, speedo, shift points, ABS, etc., can change, sometimes, not for the better. The vehicle is programmed for one thing, while the Owner has effectively changed the gearing to something else.

In my example, I'm within 3%. In yours, you're more than double out. This gives weight to the Dealer wanting to put the car back to baseline before going further.

I cannot explain the delay in logic, why the car is struggling now. And the tire size difference might not be the issue. But we do not have data to say otherwise. We know what the factory programmed the car for, not what the limits of the sensors and logic are.

People can and do exceed limits all the time. Without issue. Maybe yours is a problem. Maybe not.

Hopefully, someone with a similar change will see this thread and offer feedback. Unfortunately, I suspect the Dealer will continue to want to operate with a known baseline, before proceeding.

[/QUOT

I'm attaching some screenshots, comparisons of your before/after tire and rim selections.

While I do not know what the limit is, the circumferences of your tires are more out than I'd be comfortable with.

A general rule to follow is to keep the circumference of the new set within 3% of factory. Otherwise, speedo, shift points, ABS, etc., can change, sometimes, not for the better. The vehicle is programmed for one thing, while the Owner has effectively changed the gearing to something else.

In my example, I'm within 3%. In yours, you're more than double out. This gives weight to the Dealer wanting to put the car back to baseline before going further.

I cannot explain the delay in logic, why the car is struggling now. And the tire size difference might not be the issue. But we do not have data to say otherwise. We know what the factory programmed the car for, not what the limits of the sensors and logic are.

People can and do exceed limits all the time. Without issue. Maybe yours is a problem. Maybe not.

Hopefully, someone with a similar change will see this thread and offer feedback. Unfortunately, I suspect the Dealer will continue to want to operate with a known baseline, before proceeding.

thanks Skye. If I change the rears to 295/30/20, the diameter is 27” & revs/min are 770. Much closer to stock. Would I need to change the fronts too

 

[AZ_Ryan]

Thanks Skye for the advice & the tire comparison tool. I responded earlier but didn’t hit post. Took wheels to dealer today. Spoke with mechanic. Says there is a “SSM” about it. Pretty sure it’s the new tires being too tall. Says the camera in the windshield has to see the road to gather data for the computer. By having taller tires, thinks camera can’t see road. Also, can’t switch to normal cruise control because if you have adaptive cruise, it uses wheel sensors AND camera data. If no adaptive cruise control, uses only wheel sensor data. That why I can’t just change to normal cruise control cruise control.
If stock setup fixes problem with a repeat calibration, then I will probably get new all season tires for the 20” wheels that match my stock front 19” setup. May not have to change rears.
side note - dealer can’t use Forscan to adjust speedometer for different tires but says Whipple tune can be purchased & it has adjustment tool for tires/speedometer. However, Whipple tune is specific to just one VIN but Forscan can be used on any vehicle.
Learning new stuff.

That makes sense. Interesting explanation for the problem your having. Let us know if the stock tires fix the issue.

 

[Ken H.]

Stock tires/wheels in place. System re-aligned. Problem solved. Adaptive & normal cruise control working. Dealer was awesome. Only charged labor for exchanging wheels. Since I had a replace CCM code, warranty covered the rest -$1,000. Now I’ll probably change the front tires on the Ferrada wheels to 275/30ZR20 since they are nearly the same diameter as stock.

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