Cruise Control Speed not Matching Speedometer or OBDII Speed

[rmkilc]

My 2015 Explorer's cruise control speed does not match the speedometer. With it set at 60 mph, the vehicle's speedometer shows a little under 59 mph. I know analog speedometers have a tolerance range, but I pulled up engineering test mode and confirmed as shown below.

Just to make sure adaptive cruise control wasn't causing this, I disabled it. Same result.

I did find a TSB. TSB #44856. But it doesn't say much and leads me to believe it is only talking about the analog gauge which we know aren't perfect. I don't see why a digital cruise control speed shouldn't match the digital speed of the vehicle. I could understand fluctuations below the set speed as it adjusts for the terrain, but it is constantly over 1 mph off. I even set the IPC to kilometers to see if cruise control in kilometers matches the engineering test mode km/h readout to see if perhaps Ford programmed the vehicle in metric and accuracy is lost when converting to imperial due to rounding or something. But the same issue exists there too.

Does anyone know a way to calibrate it?

 

[peterk9]

Mine is off by 2 kmph. I have the digital speedometer display in the center and the analog one on the right. I believe the analog is the accurate one so when I set my cruise control speed by the digital one I set it at 62 if I want 60 kmph. No idea how to calibrate it and have brought up the question several times. I did manage to get my Estimated MPG to match the actual but I don't believe you can do it on a 2015.
Speedometer Accuracy

Peter

 

[KayGee]

My PIUs have "calibrated speedometers" and both are off by 1mph compared to several GPS I have.

For me personally, this issue ranks a 0/10 on my give a $hit meter.

 

[rmkilc]

My PIUs have "calibrated speedometers" and both are off by 1mph compared to several GPS I have.

For me personally, this issue ranks a 0/10 on my give a $hit meter.

I also don't care if my speedometer is off from actual speed by 1 mph. But nothing in my original post is about accuracy of the speedometer so that is beside the point. I was only talking about the cruise control set speed readout not matching the speed the vehicle thinks it is going.

It is quite annoying, and having to always set it at 61 or 62 to go 60 kinda defeats the whole purpose of having the digital cruise control readout. I would almost prefer the old school cruise control setup with no set speed readout over this if it's not going to work properly.

 

[KayGee]

Sorry, my point was more that mine says it is calibrated and still has a margin of error. I don't worry about it or cruise control speed matching my gps or speedometer or obd2 speed readout or whatever either. 1 or 2 mph difference amongst any of them ranks 0/10 for me.

It seems like this issue must be really troubling to you though. I apologize for any insensitivy that may have come across in my posts.

 

[Adrian Gitch]

Mine off by 1 or 2 also. My '17 Expedition is as well along with our Camry and my son's Camry. Almost every vehicle I've owned has been off by 1 or 2 from what the cruise was set at. I recommend to just set the cruise a couple mph's higher.

 

[Flying68]

The gauge is affected by tire size, wear, mechanical error, etc. I have found through comparison that the cruise displayed set point matches my GPS readout on my phone almost perfectly. This leads me to believe the cruise is corrected by the vehicles GPS signal. I once had a 55 series tire on for a couple of weeks (they ordered or received the wrong size) and the gauge was off by 3-4 mph at 70 mph, once the 50's were on, it was back to 1-2 mph difference at around 70 mph.

 

[rmkilc]

The gauge is affected by tire size, wear, mechanical error, etc. I have found through comparison that the cruise displayed set point matches my GPS readout on my phone almost perfectly. This leads me to believe the cruise is corrected by the vehicles GPS signal. I once had a 55 series tire on for a couple of weeks (they ordered or received the wrong size) and the gauge was off by 3-4 mph at 70 mph, once the 50's were on, it was back to 1-2 mph difference at around 70 mph.

Hmm, that is an interesting theory. It would seem odd though if an auto manufacturer would use the GPS to correct for the cruise control display but not the OBDII speed and speedometer. I'll have to check it against a GPS to see if the cruise display matches.

 

[jhu8]

Just tested my 17 today against Waze with Android auto and it the speeds correlated. Although I have had vehicles that didn't match perfectly.

 

[Jon M]

Mine is also runs 1 mph lower than set, as described.

 

[rmkilc]

Just tested it against my phone's GPS and the OBDII speed was within 0.2 of a MPH. The set cruise control speed is the one that's off from my phone's GPS so I highly doubt the vehicle is correcting cruise control speed with it's GPS. Unless my phone is off.

 

[Dennis J.A.A.]

If I am SET at 60 MPH on CC my digital readout and my analog are the same saying 59 MPH.
For me it is an OCD problem!

 

[peterk9]

Hmm, that is an interesting theory. It would seem odd though if an auto manufacturer would use the GPS to correct for the cruise control display but not the OBDII speed and speedometer. I'll have to check it against a GPS to see if the cruise display matches.

FYI, I realize that this is the 5th gen forum and perhaps this is not what you meant but the GPS does affect the ACC in the 6th gen. So it is quite possible that there is also communication between the vehicle and GPS in the 5th gen.
When I take the on-ramp to a major highway where the speed limit is 110 kmph from a secondary road where the limit was 80 kmph the vehicle will suddenly display the 110 sign in the dash even though it has not passed a sign indicating the new limit. The only place it could have received that info is from the GPS.

Peter