Intermittent Speedometer/Odometer

[Puckboy106]

Hello Forum! Need some help/advice.

I searched the forums and am getting pretty confused all around, so let me boil it down for everyone.

98 Explorer XLT, 275K miles.

Recently, the speedometer will be working just fine and then without warning just drops to zero and stops working. If I get to a stop, shut off the engine, restart, the speedometer starts working, but could drop at any minute. During a longer trip, the speedometer can drop, then start back up, drop to zero etc etc.

So I tested the Cruise control. SOLID. Despite the action of the speedometer, Cruise control is stable and fine.

I replaced the VSS on the rear dfferential. No change, Speedometer/Odometer still intermittent.

Is my next step to tear out the instument panel and replace the work gear?

Any suggestions?

Thanks,

John

 

[Chikar]

Hi John;

I'm looking at the circuit diagram for your speedo. The speedo and odometer are both electrically driven, there is no cable involved.

The Ford manual gives a diagnostic procedure measuring voltages and resistances in the cluster, with a drawing to show the test points. Unfortunately, while I can copy the text of the procedure and paste it into a reply the drawings don't paste for some reason.

One of the tests is for 12Volts to the instrument cluster. If the other gauges continue to work normally you can assume that's not the problem.

The rest of the test involves resistance tests between connector pins and the speedometer pins. I'll paste them below, without the helpful drawings of course.

PINPOINT TEST E: PINPOINT TEST E: THE SPEEDOMETER/ODOMETER IS INOPERATIVE
CONDITIONS DETAILS/RESULTS/ACTIONS
E1 CHECK THE VOLTAGE TO THE INSTRUMENT CLUSTER




Instrument Cluster


Measure the voltage between instrument cluster C288-7, circuit 1001 (W/Y), and ground.


Is the voltage greater than 10 volts?
Yes
GO to E2 .

No
REPAIR circuit 1001 (W/Y). TEST the system for normal operation.

E2 CHECK THE INSTRUMENT CLUSTER PRINTED CIRCUIT


Instrument Cluster


NOTE: Measurements must be made to the speedometer gauge pins that are inside the instrument cluster printed circuit clips.
Measure the resistance between the speedometer pins (which can be seen in the middle of the instrument cluster printed circuit clips) and the corresponding instrument cluster terminal. Refer to the table for the pin and terminal assignments.
Instrument Cluster Terminal Speedometer Gauge Pin
C286-13 B
C287-1 S
C287-2 G
C288-7 BATT



Are the resistances less than 1 ohm?
Yes
GO to E3 .

No
REPLACE the instrument cluster printed circuit. TEST the system for normal operation.

E3 CHECK CIRCUIT 679 (GY/BK)


Anti-Lock Brake Control Module C186


Measure the resistance between anti-lock brake control module C186-10, circuit 679 (GY/BK), and instrument cluster C287-1, circuit 679 (GY/BK).


Is the resistance less than 5 ohms?
Yes
REPLACE the speedometer. TEST the system for normal operation.

No
REPAIR circuit 679 (GY/BK). TEST the system for normal operation.

I've been a electronics and computer tech for years and years. Intermittent problems like yours are the worst to track down.

Hope this helps

 

[Puckboy106]

This is great help!!! Thank you!

 

[Twist Of Fate]

What did you come up with? I have the same problem and have already replaced the VSS. Mine only works when it is under 30 degrees outside and the truck is cold. As soon as the truck runs for a couple minutes or I hit 55, it drops and worn't work again for days. I'm dreading tearing the dash apart, but 2 years with no spedo is getting old!

 

[trentlance]

same speedo problem

Thing works for a few minutes when its cold and then drops
Any ideas to fix this one
I keep having to use my gps as my speedo
Thanx

 

[mir]

I am also having the intermittent speedo problem. My problem start in the morning when I am running with lights on. Approximately 25 minutes into trip the speedo and odometer quit working. In the afternoon I have no problems. Seems to me that when I adjust dimmer switch to low dash light speedo problem take longer to appear. Could this be a heat issue?