Mystery remains: Why does my odometer advance when in Park?

[parker_lansing]

Since I bought my 2003 Sport Trac XLT back in March 2023, the speedometer has bounced around when idling (parked or in gear), but when I'm driving more than about 15 mph, the needle snaps into place where it should be. When I slow down under 15mph, the speedometer starts bouncing around again, from 0mph to 15mph.

After a few months, while waiting at a drive-thru, I noticed that the tenths digit on my trip odometer was advancing at idle.

I spent an hour or so experimenting with this and taking notes, and I found that when in Park or at idle in Drive, the odometer was advancing as if I were going 6mph, even though the vehicle was at a stop.

This corresponds with the speedometer bouncing around, if the average is (15mph - 0mph ) / 2) = 7.5mph (close enough to what the odometer was telling me).

And this was happening consistently for both the trip odometer and the regular odometer.

I had all sorts of theories, from a malfunctioning dash console, to a transmission slippage problem, to an odometer gear problem.
I figured it was going to be expensive, so I tried to ignore it for a while.

But yesterday, I got my truck back from the following service:
- plugs, wires, air filter
- check transmission fluid (right where it is supposed to be)
- replace serpentine belt and tensioner

And, to my surprise, both the speedometer and odometer issues were gone!

Update: The problem went away for two weeks, and has suddenly returned.

Can anyone explain this for me?

 

[Blown09]

I would be more inclined to think the wires may have been the issue(if it’s actually gone, and not just intermittent). High voltage leaking into the vehicle can cause some funky stuff.

I’ve read that those clusters do have issues, so it could be still there, just not acting up currently. Did the battery get disconnected during the work?

 

[parker_lansing]

I did find a comment that supports your assertion. It is a compelling argument.

My radio station presets are intact, and my clock is accurate, so I don't believe the battery was disconnected.

Update: You were right, the problem returned yesterday, so it is intermittent!

 

[DILLARD000]

You have the 2003 pre-HEC electronics, so easier to maintain than 2004+Later HEC electronics.
I'd first start by taking InstrumentCluster out (requires first removing DashCenterPanel), giving it a thorough cleaning with ElectricalCleaner\RubbinAlcohol & QTips,
lube Speedo\OdoMeter mechanism with a little SiliconeSpray,
carefully clean+tighten all electrical Cable+Bulb+FlexCircuit+Ground connections,
install new Bulbs; preference here is traditional\simple IncaBulbs,
not LEDs of unknown\complex\questionable design+endurance.

BackLamps
LitBulbs T10mmWedg*23mmLong 12volt 3\4watt Sylvania# 161\194
Sockets T10mmWedg*13mmCircuitHoleMt FordMotorCraft# c80z-13711-b
* Do Not Use Higher Wattage Bulbs, They Will Melt Plastic Sockets
* 6each In DashLeft InstrumentCluster
* 2each In DashCenter AirConSelectors

DutyLamps
LitBulbs T5mmWedg*18mmLong 12volt 9\13watt Sylvania# 906\912
Sockets T5mmWedg*7mmCircuitHoleMt FordMotorCraft# f57z-13b765-ba
* Do Not Use Higher Wattage Bulbs, They Will Melt Plastic Sockets
* 16each In DashLeft InstrumentCluster

Click here for more info on InstrumentCluster+DashLamps.
This is a tedious\slow\boring but relatively simple job,
best done on a quiet Saturday\Sunday afternoon with a couple of cold beers & a little patience.
Hopefully this helps.

 

[kent Gorham]

Since I bought my 2003 Sport Trac XLT back in March 2023, the speedometer has bounced around when idling (parked or in gear), but when I'm driving more than about 15 mph, the needle snaps into place where it should be. When I slow down under 15mph, the speedometer starts bouncing around again, from 0mph to 15mph.

After a few months, while waiting at a drive-thru, I noticed that the tenths digit on my trip odometer was advancing at idle.
I spent an hour or so experimenting with this and taking notes, and I found that when in Park or at idle in Drive, the odometer was advancing as if I were going 6mph, even though the vehicle was at a stop.
This corresponds with the speedometer bouncing around, if the average is (15mph - 0mph ) / 2) = 7.5mph (close enough to what the odometer was telling me).
And this was happening consistently for both the trip odometer and the regular odometer.

I had all sorts of theories, from a malfunctioning dash console, to a transmission slippage problem, to an odometer gear problem.
I figured it was going to be expensive, so I tried to ignore it for a while.

But yesterday, I got my truck back from the following service:
- plugs, wires, air filter
- check transmission fluid (right where it is supposed to be)
- replace serpentine belt and tensioner

And, to my surprise, both the speedometer and odometer issues were gone!

I suspect that a loose serpentine belt was to blame for this issue.

But I don't know why.

Can anyone explain this for me?

I know on my old Honda, the rpm’s are measured at the coil. So I suspect the new wires had something to do with it but I am no mechanic as my wife reminds me constantly.