Analog speedometer does not match digital speedometer by a lot

[airline tech]

I have dug into the manuals, cannot find anything as a direction for cause.
There are too many variables and modules that tie into the Speedometer.
Without a code I'm ?‍, for some reason the manual is vague on this subject. It dances around the modules and codes and live data PID's.
It may take a drive cycle while viewing live data pIds to see whats dropping.
I can say that it is a communication issue, somethings getting lost, and I see no troubleshoot direction on a split in the difference between the Digital and Analog Gauge

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[got3fords]

The 'analog' gage is not actually analog, is it? I mean it runs off a digital signal right?

 

[Msfitoy]

The 'analog' gage is not actually analog, is it? I mean it runs off a digital signal right?

Yes, it's digital signal fed to an (electric) analog readout gauge...

 

[Burnt Money]

Mine has had a difference of 2-3MPH since new. It hasn’t changed in 60k miles. I don’t really notice it that much anymore. Still kinda drives me crazy knowing they don’t match.

 

[Grandaccess]

Never messed with it myself. The first pic says 'average speed' so that's not gonna match. The second pic, I dunno.

Pay attention next time you run through one of those speed displays where they set up a radar station showing your speed, and see which one matches.

I have an App on my phone for Sat. speed, I am off 10% because of my tires 285/70 (33) my ODO reads 60 and Sat speed is 66 mph I never looked into changing it inside ford scantool one of these days I might?

 

[Fx4ranger2019Larait]

I have an App on my phone for Sat. speed, I am off 10% because of my tires 285/70 (33) my ODO reads 60 and Sat speed is 66 mph I never looked into changing it inside ford scantool one of these days I might?

I have 285’s also but I changed that on Forscan believe you have to change tire circumference in mm. I tested a lot and checked it with Waze the magic number was around 2500 mm. I’d have to open up Forscan to check the exact number. The digital is almost ? accurate now… Maybe .1 at 75-80mph.


Also the random analog difference drives me crazy. Not as a big deal when it’s over but sometimes it will go under. The analog says 30 or 40 and I’ll be going 50. Easy way to get a ticket if you’re not paying attention. And when I come to a stop it will bounce on 0 for a while before it finally resets sometimes after I turn off the truck. I have no pictures or videos next time I’ll try to take a video of that.

 

[Msfitoy]

I have 285’s also but I changed that on Forscan believe you have to change tire circumference in mm. I tested a lot and checked it with Waze the magic number was around 2500 mm. I’d have to open up Forscan to check the exact number. The digital is almost ? accurate now… Maybe .1 at 75-80mph.


Also the random analog difference drives me crazy. Not as a big deal when it’s over but sometimes it will go under. The analog says 30 or 40 and I’ll be going 50. Easy way to get a ticket if you’re not paying attention. And when I come to a stop it will bounce on 0 for a while before it finally resets sometimes after I turn off the truck. I have no pictures or videos next time I’ll try to take a video of that.

I got mine within +- one mph too...

 

[Jacob]

So this is related to tranny issues since the sensor is inside the tranny??

 

[REDWM]

Hook up scanner and scan for codes, you will most likely have a stored code.
Do a IPC, ABS and PCM - Self Test as well with the Scanner or Forscan

ABS reports to PCM and PCM reports to the GWM, which then displays the Speed.
You are losing a communication somewhere.
IPC defaults to last known speed if com is lost for more than 5-seconds.

With a scan tool you can also command the Speed Odometer to increase in 10% increments for testing.

Again, what is ABS not he brake system) and GWM.

 

[airline tech]

Again, what is ABS not he brake system) and GWM.

ABS = Anti-Lock Braking System - In the event of a skid when applying brakes, it pulses the brake pressure to stop the wheel that is (skidding), this is felt by the brake pedal pulsating and the sound of the ABS Module activating.
Wheel Speed is received by the wheel speed sensors at each wheel and reports this info to the PCM.

PCM = Powertrain Control Module - Main controlling module for engine controls, so in this instance the PCM always knows vehicle speed via the ABS reporting to the PCM, the PCM reports this information to the GWM.

The PCM also receives input from the OSS / VSS or also known as the VSO.
Output Speed Sensor / Vehicle Speed Sensor / Vehicle Speed Output, the sensor is located in the transmission and can be programmed (To account for Tire Size) changes.
So, with the above is just like an old school sensor without the physical cable.

NOTE: This is where the manuals fall short, as to exactly which of the sensors actually report the Vehicle Speed and displays it on the IPC.
My logical thinking it is the OSS, for the speed display and the PCM is looking at both the ABS input and OSS input and using both as a reference. (Comparision Reference)
One factor for this is due to the fact that wheel speed sensor input will change when Appling the brake.
So, in regard to the fault in this thread, there is a communication drop of speed information, something is mis-reporting the information or dropping off.
The IPC gets lost and defaults to the last known reported speed. (32-MPH)

GWM = Gateway Module, this is the main module in the whole truck that see's everything from every module on the truck and communicates between all the modules via the (CAN - Data Bus)
So basically, the GWM is nothing more than a pass-through device.
When you plug in a (Scanner) into the OBD Port, you are directly connecting to the GWM.
For this instance (Vehicle Speed) the GWM forwards and displays the speed it is receiving to the IPC (IPC = Instrument Panel Cluster)
Think of the GWM as Big Brother, sees all knows all.

CAN Bus = Controller Access Network, it is a communication data bus linking all the modules in the truck, so every module that needs shared information from other related system modules can be seen by all modules.

So, with the Ranger speed odometer readings on the IPC are more complex than an old school (Speed Sensor - Mechanical Gear) driving a cable that is connected to the back of the IPC.
It is a little more complex.

 

[REDWM]

ABS = Anti-Lock Braking System - In the event of a skid when applying brakes, it pulses the brake pressure to stop the wheel that is (skidding), this is felt by the brake pedal pulsating and the sound of the ABS Module activating.
Wheel Speed is received by the wheel speed sensors at each wheel and reports this info to the PCM.

PCM = Powertrain Control Module - Main controlling module for engine controls, so in this instance the PCM always knows vehicle speed via the ABS reporting to the PCM, the PCM reports this information to the GWM.

The PCM also receives input from the OSS / VSS or also known as the VSO.
Output Speed Sensor / Vehicle Speed Sensor / Vehicle Speed Output, the sensor is located in the transmission and can be programmed (To account for Tire Size) changes.
So, with the above is just like an old school sensor without the physical cable.

NOTE: This is where the manuals fall short, as to exactly which of the sensors actually report the Vehicle Speed and displays it on the IPC.
My logical thinking it is the OSS, for the speed display and the PCM is looking at both the ABS input and OSS input and using both as a reference. (Comparision Reference)
One factor for this is due to the fact that wheel speed sensor input will change when Appling the brake.
So, in regard to the fault in this thread, there is a communication drop of speed information, something is mis-reporting the information or dropping off.
The IPC gets lost and defaults to the last known reported speed. (32-MPH)

GWM = Gateway Module, this is the main module in the whole truck that see's everything from every module on the truck and communicates between all the modules via the (CAN - Data Bus)
So basically, the GWM is nothing more than a pass-through device.
When you plug in a (Scanner) into the OBD Port, you are directly connecting to the GWM.
For this instance (Vehicle Speed) the GWM forwards and displays the speed it is receiving to the IPC (IPC = Instrument Panel Cluster)
Think of the GWM as Big Brother, sees all knows all.

CAN Bus = Controller Access Network, it is a communication data bus linking all the modules in the truck, so every module that needs shared information from other related system modules can be seen by all modules.

So, with the Ranger speed odometer readings on the IPC are more complex than an old school (Speed Sensor - Mechanical Gear) driving a cable that is connected to the back of the IPC.
It is a little more complex.

Thanks, that helps a lot when reading your very informative threads.

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