DO NOT ORDER TIRES FROM TIRERACK.COM! F- customer service

[Paul Chin]

What year is your car, it's not in your Signature.

 

There is a TSB 14-0037 for correcting GPS problems but it's for cars built before 1/6/2014.

http://fordfusionhybridforum.com/topic/9352-technical-service-bulletins-tsbs/?p=87989

 

2013 FFH SE, and I just found out about this TSB yesterday. I guess it is a problem with the GPS unit and not the tires, but I still find it odd that I've had my car for a year and a half and never had problems with the GPS until now.

[hybridbear]

 

The system calculates the steering angle and timing based on the distance it assumes the car is going to travel for a given number of wheel revolutions. So for example in the middle portion of the parking job, when you're backing in at an angle, you're going to travel 3% further than the computer thinks you are, so you're going to be that much closer to the curb.

 

The sensor does detect the two vehicles, but only as you go past them (it's only one sensor, in the front bumper, one on each side of the car). Once the system senses the parking space, it calculates where you are in relation to that space and then calculate the steering required to get you into that space. Once the active park starts, the sensors don't do anything else, it's all based on the distance traveled as measured by the wheel speed sensors. So basically tire diameter is absolutely critical to proper APA function.

You're right. I meant that the front & rear sensors still beep to let you know how close you're getting to the vehicle in front & behind.

[Waldo]

Tires would not affect GPS position, ACC or HUD.

 

Totally incorrect. Just like the APA system, the GPS uses the distance calculated from the wheel speed sensors for it's "dead reconning" mode. If you're traveling in cities with lots of tall buildings or through tunnels, the GPS will use the wheel speed to continue to calculate your position on the map. If you're tires are a different diameter, these calculations will be off.

 

The ACC system also relies on the calculated vehicle speed to determine it's closing rate. It uses radar to sense objects in front and figure out how far away they are, but then it uses the vehicle speed (as calculated from the wheel speed sensors) to determine how much to slow down, how much brake to apply and so on. If the change in vehicle speed doesn't match the calculations, then you end up in a hysteresis loop where instead of maintaining a steady gap, the systems keeps closing, then backing off, then closing again. Not a huge deal and the system will still work, but depending on how far off the wheel speed is, it can be annoying. It also means the HUD warnings would be activated just a touch later than what you might expect, since the vehicle is traveling a bit faster than the system thinks it is.

[Texasota]

 

Just like the APA system, the GPS uses the distance calculated from the wheel speed sensors for it's "dead reconning" mode. If you're traveling in cities with lots of tall buildings or through tunnels, the GPS will use the wheel speed to continue to calculate your position on the map. If you're tires are a different diameter, these calculations will be off.

 

Does this mean as the tire diameter becomes smaller due to normal tread wear these problems you have described will become noticable?

[lolder]

I don't think 3% would upset the ACC servo loop and the dead reckoning mode is a "loss of GPS" data mode so it doesn't affect the GPS mode. 3% is about 150 feet /mile for which you would have to lose your GPS for a minute or two. I'll wager the dead reckoning mode is also announced in some manner.

Edited December 9, 2014 by lolder

[GrySql]

From the Wiring Manual:

 

Vehicle Speed Functional Overview
The hybrid vehicle uses three methods to calculate vehicle speed. The PCM (Powertrain Control Module) uses the ABS signal if available, and will substitute the motor speed if the ABS signal is missing. The PCM will use the engine and generator speed calculation if both the ABS and motor speeds are unavailable.

1. Vehicle Speed From The Anti-Lock Brake System (ABS) Module
The ABS module calculates wheel speed from the front two wheel speed sensors and sends this information to the PCM through the communication network.

 

2. Vehicle Speed From The TCM (Transmission Control Module)
The TCM calculates traction motor speed from the traction motor resolvers and combines it with (PCM stored) tire size and axle ratio data to determine vehicle speed. This calculation is then sent to the PCM over the communication network.

3. Vehicle Speed From Engine And Generator Speed
The TCM calculates generator speed from the generator resolvers and sends this information to the PCM. The PCM combines input information from the generator speed and engine speed along with tire size and gear ratio to calculate a vehicle speed.

The PCM strategy cross checks all the inputs to determine if they agree with one another.
===============

From the Workshop Manual.

This was describing the GPS signal loss and the ABS message to the AIPM (SYNC) module.:

 

Navigation rolling wheel count and direction ABS module. > This message provides for more accurate tracking of the vehicle position when the GPS signal is temporarily unavailable for gear lever position for vehicle direction data for navigation.

 

To the GPSM:

Navigation rolling wheel count and direction ABS module. > Used to verify the gear lever position for vehicle direction data for navigation.

 

Navigation - If Equipped
The navigation system guides the user to a pre-entered destination. Map data is read from the map data SD card plugged into the media hub. The APIM calculates route information based on GPS data received by the GPSM. The APIM also uses vehicle speed and transmission gear selected signals received through the network to detect vehicle speed and direction, resulting in more accurate navigation tracking. The navigation display is shown on the FDIM.
The compass heading is derived from the GPS antenna signal. There are no serviceable parts for the compass.
The voice recognition system allows the user to interface with the system without using the touchscreen. A microphone located in the headliner provides a direct input to the APIM.

[Waldo]

I don't think 3% would upset the ACC servo loop and the dead reckoning mode is a "loss of GPS" data mode so it doesn't affect the GPS mode. 3% is about 150 feet /mile for which you would have to lose your GPS for a minute or two. I'll wager the dead reckoning mode is also announced in some manner.

 

That's great that you don't think that it will affect it, but the Ford engineers who designed the system do. Obviously the bigger the difference the more noticeable it will be, but the Lincoln MKS comes with 19in and 20in tires that are only 2% different and it is noticeable on that if you switch the tires without reprogramming the computer.

[obob]

Perhaps in the future the software will use the GPS to compute the size of the tires, and adjust that size as they wear out. ( Sorry in advance if this has already been said in more technical terms )

[Corey Sullivan]

Not exactly related to Tirerack, but I just had a dealer refuse to install an alternate tire size on my 2010 FFH. Took my car to the local Ford dealer Quicklane with tires I purchased from a friend and thought they could throw them on while they were doing an oil change. Spec on the car calls for 225/50R17 yet I've found on most websites when looking for tires that 215/50R17 is an acceptable alternative for the car. The dealer claimed they wouldn't install the tires as it may hurt the hybrid drivetrain. I have no idea how less than a half inch difference could possibly hurt anything other than possibly driving performance. Had me a little cautious since it was the dealer service center telling me this and my google search led me here. We are talking -1.5% tire diameter difference! I lost interest in dealing with these guys again when he went on to tell me that he could put them on if they were 225/55R17...turns out that is also not exactly OEM diameter and is +1.5%. Lost faith in what I though was a reputable operation. Anyone else had greif when trying to run a smaller width tire that didn't match OEM tire diameter?

[GrySql]

Costco will not replace tires unless the size is in the manufacturers matrix for that particular make and model.

[lolder]

QuickChange is a loss-leader that drums up other business. They refused to rotate my tires once because one of them had a plug in the edge of the tread. They'd sell me a replacement for $250. They overfilled the oil also which I had my mechanic remove. I haven't been back since.