Why is speedometer reading wrong?

BRIANPOSEY

MEMBER
1997 PLYMOUTH VOYAGER
200,000 MILES

I have a 97 Plymouth Voyager with a 3.0 and 3 speed tranny I have been fixing back up. I did notice the speedo was showing a wrong speed. Maybe 10 - 15 mph off. I went and did the pcb resolder to fix the gas gauge problem and thats solved but why is the speedo off? I did the dash calibration test and the only codes that show up are in the beginning of the test (Code 999 then Code 0). When it starts sweeping the needles, the speedo goes from o to 10, then to 45, then to 65 then all needles drop and goes to next test. When done, I am left with the tripometer and no codes.

Does it need some type of speed calibration or is it a sensor? Is there something I can do or does it need to go to a shop?

3 Replies

KHLOW2008

MECHANIC
41,814 POSTS

It could be the speed sensor or the speedometer itself. How sure are you that it is off? Is it faster or slower than expected?
Are wheels the specified size?

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Sunday, October 14th, 2012 AT 5:39 PM

BRIANPOSEY

MEMBER
21 POSTS

Ahh. Didn't even think of that. Apparently Orig. Tires are 205/75 R14. It has 195/70 R14's on it. The speedo was reading under what I think I was going. Had to web search the original size.
Another thing I see (may or may not be related), on youtube, all the calibration test for voyagers and cross related models show the speedo going to 20, 55 then 75 BUT none of them are my same dash. Hmmmm.