Speedometer/Odometer Intermittent Quits Working 1997 Explorer Sport

I have a 1997 Explorer Sport with the 4.0 SOHC engine, Automatic. My speedo seems to do what it wants. Sometimes it doesn't work at all and others it fluxuates. And still others it seems fine or reads what seems like too high. The cruise control works fine no matter what the speedo is doing and the trucks runs fine with no other issues. Could it be the speed sensor or something else. Also the research I have done on this site mentions a speed sensor at the wheels for antilock as well as one on the tail end of the transmission. Which one would I be looking at to be the culprit if it is a speed sensor issue? Thank you in advance for your response.

David

Reply to
DBray
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A friend of mine had a similar problem on a 1994 and it turned out to be the speedometer head (the part in the dash).

Reply to
Tommy Wood

I believe by 1997 the speedo is electronic (like a tachometer), i.e. it uses the VSS (vehicle speed sensor) signal to calculate the speed. This is a pulse generator driven by the transmission. It puts out pulses, and the vehicle speed can be calculated by the time between pulses- the faster you go, the shorter the time between pulses. The cruise control also uses this signal, in fact my '94 explorer has a mechanical speedo but also has a VSS for the cruise control.

So- since your cruise control works fine (very smart of you to include that bit of info) your VSS is obviously working. I'd can think of three possible causes:

  1. You have a bad connection in the VSS signal somewhere between your speedo and the the point where the VSS signal to the speedo branches off from the cruise control. This would be an intermittant open, not a short, because a short would also kill the cruise control at the same time.
  2. Your speedo is not getting power, or has a bad ground. It's electronic, so it needs power to amplify and process the VSS signal to drive the speedo and odo.
  3. A bad connection in the speedo assy- corrosion, a bad solder joint, something like that.

Just because there are more things to go wrong, I'd guess the speedo itself to be the most likely culprit. When you're driving down the road and it stops working, try smacking the dash near the speedo with your hand to see if jarring it makes it start working again.

Tracing out the wiring is a tough job, even getting access to them is tough. In general, I'd expect the VSS wires to go from the transmission to the cruise control, and then to the speedo. So you could inspect and wiggle the connectors going to the cruise control under the hood, the ones behind the dash are going to be very hard to access. As I said, since the cruise control works, focus on the speedo and the wiring between the cruise control and the speedo, the VSS and wiring from there to the cruise control must be good.

Good luck,

-Paul

Reply to
carbide

This happened to my '91 in, oh, about '96. The speedometer needle would oscillate wildly back and forth, and after about a month of this just fell to the peg and didn't move again. The cruise control and odometer still worked fine, though. About two years later I hit a sharp bump and the speedometer started working again - it has been fine ever since.

Reply to
John D. Goulden

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