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?

 

[user 78012]

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.

 

[parker_lansing]

Ok, more evidence in this front. I had the truck in for service over the past week, and they didn't see the problem present itself. But the clock was reset, which means the battery was disconnected. This is the second time that has happened. All signs point to electrical. I expect the symptoms to come back in a week or two.
Secondly, I crawled underneath the truck, and found that there are two ground straps (one on each side of the vehicle) that connect the frame to the body. Both are totally severed. I'm going to fix these and report back (in a month or so).

 

[DILLARD000]

Ok, more evidence in this front. I had the truck in for service over the past week, and they didn't see the problem present itself. But the clock was reset, which means the battery was disconnected. This is the second time that has happened. All signs point to electrical. I expect the symptoms to come back in a week or two.
Secondly, I crawled underneath the truck, and found that there are two ground straps (one on each side of the vehicle) that connect the frame to the body. Both are totally severed. I'm going to fix these and report back (in a month or so).

Too often critical frame\ground wires\straps are left disconnected or are a neglected maintenance item.
Modern vehicles have an ever increasing number of electrical\electronic sensors+actuators+computers,
that all require a dependable\stable 12v+ supply and also a solid body\frame ground for the return half of those circuits.
When DC ground wires\straps get loose\broken\disconnected, weird\crazy things start happening.

 

[clandress]

If you live where the roads are salted you should replace the ground straps with heavy insulated wire.

 

[parker_lansing]

Too often critical frame\ground wires\straps are left disconnected or are a neglected maintenance item.
Modern vehicles have an ever increasing number of electrical\electronic sensors+actuators+computers,
that all require a dependable\stable 12v+ supply and also a solid body\frame ground for the return half of those circuits.
When DC ground wires\straps get loose\broken\disconnected, weird\crazy things start happening.

How many ground straps are there? I had the main ground strap replaced last year - it was falling apart.
I see the smaller broken straps on either side of the vehicle, from body to frame.
Are there others? Is there a definitive list somewhere?
I saw some mentions of one under the center of the bed, one on the fuel filler pipe, and one on the hood, but I'm not certain if those were Sport Tracs or not (was on Explorer forum).

 

[Roy Trolinger]

I had the same problem. Try replacing the transmission sensor first (easy & cheap).
I ended up having to replace the speedometer gauge with a junkyard part. I moved the odometer to over to the new speedometer.
Calibration is a little tricky...use a fork to pop off the needle and find a straight stretch of road. Using a GPS (or your phone), stick the needle back on to match the speed your phone says.

 

[parker_lansing]

I had the same problem. Try replacing the transmission sensor first (easy & cheap).
I ended up having to replace the speedometer gauge with a junkyard part. I moved the odometer to over to the new speedometer.
Calibration is a little tricky...use a fork to pop off the needle and find a straight stretch of road. Using a GPS (or your phone), stick the needle back on to match the speed your phone says.

Well, even after all of my ground straps are replaced, I still have this intermittent issue. I'm going to take your advice and try replacing the transmission sensor. The transmission has to be dropped anyway, so I may as well do everything at once. Thanks for the recommendation.

 

[parker_lansing]

If you live where the roads are salted you should replace the ground straps with heavy insulated wire.

Yes, I agree. The shop that did the work (Detroit Garage in Lansing) put extra heavy ground straps on it.