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On my way out of town a few days ago the last digit of my odo started going dim (which has happened occasionally in the past). Didn't think much of it. I towed about 175mi to my destination and stopped. Shut the truck off for about a half hour, and when I started it back up the speedo decided that anything over about 5 mph was full speed. When you come to a stop the speedometer goes back to 0. There is a fine line in the the 5-10mph range that it'll read between 50mph and 85.
I do have a scanner, and checked out the speed reported to the pcm and that is correct. The transmission shifts properly, and the odo tracks properly. I towed home the same 175 miles and the truck never skipped a beat but obviously had to use GPS for speed.
I've replaced stepper motors in other clusters before, but this doesn't seem like a stepper problem. I can pull the cluster out tomorrow to check it out, but what would I be looking for? I searched and couldn't find any other threads like this. It's always the psom causing erratic speed and transmission problems, which I'm glad was not the failure mode this time. That would have sucked!
I don't know if this is your problem but my 94 F250 was doing the same thing. Totally erratic speedo readings after about 5 mph, bouncing between 50 and 80. It was the speed sensor located on the differential. Replaced it, problem solved. you might check this out if your truck has one.
I don't know if this is your problem but my 94 F250 was doing the same thing. Totally erratic speedo readings after about 5 mph, bouncing between 50 and 80. It was the speed sensor located on the differential. Replaced it, problem solved. you might check this out if your truck has one.
I did not start there because my pcm has the correct speed and I can see in live data that it is rock steady.
I got a replacement cluster (wanted a tach anyways I guess), hoping it was the speedometer that failed, but it ended up being the psom. The original psom on the replacement cluster did the same. Swapped the replacement psom back in and the speedo works properly again.
I reached out to a couple repair places to see if this is something they've seen and can repair. I'm doubting it, unless bad caps can cause this? There's no other signs of damage I can see (and the caps outwardly look fine but I understand that doesn't mean much).
Greetings Death Ranger,
My 95 E350 RV chassis had a real similar problem and I found that the "tantalum" capacitor had become unsoldered at its connection on the psom circuit board. In your first picture on the upper left corner you will see a yellowish rectangular component with a brown stripe, that's the part that I resoldered and my problems went away. It seems to cause a variety of driveability problems. I just barely touched mine with my pinky and it fell to the floor. Becareful of orientation before you fool with it. Hope this helps.
Ford chasis
Paul B
