I understand your concern, but this information is suggestive but not definitive. Have you tried comparing your speedometer reading to the measurement obtained with a scan tool?

 

Scott,

Today on a lark, I hooked up my Actron CP9180 scan tool to my 97 Civic DX 5-speed and went for a drive. At 30 mph, 40 mph, and 50 mph, my speedometer consistently read 3 mph faster than did the scan tool. I am not sure whether the speedometer, scan tool, or neither is correct. I thought you might want to know.

 

Interesting. While I still feel that my three reasons above are reliable because they all resulted in the exact same mph difference, maybe I should have it checked by someone who has the right equipment.

 

well if you know the mph reading is off just remember that its off and go alittle faster... when im in traffic i just keep up with the flow. usualy as long as people are still going alittle faster than you then the cop shouldnt pull you over unless you do something stupid that is

but i dont go by those road construction speed thingies. they have never been accurate on my vehicles! usualy off by about 4-5mph. i think thats why most cops give people breaks for ruffl 5mph faster than the posted speed because our speedometers are not as accurate as there radar guns!

 

2) I have checked it with those "your speed" signs at construction zones. In all other vehicles I've been in, those signs are right on.


i have done this in my vehicle and it says i am approximatly 4 miles an hour slower than it says i am going. i dont mind it at all cause i have driven side by side with another car and the other car said 60 and i look down at mine and it also said 60 but the construction zone speed things all say 4 miles an hour slower!!! WTH??

 

Clearly, various speed measuring devices (speedometer, scan tool, radar) must be properly calibrated and, if not, will give imprecise readings. I assume, however, that the speed measurements made by these various devices lie within an acceptable margin of error. For myself, I'll continue to accept the speedometer readings in my Civic as I don't see any major negative consequences to doing so.

 

Yeah, that's what I do. However it is very irritating. I don't like to have to "think" while looking at my speedometer to know what speed I'm really going. :-) Since I "learned my lesson" when I was in my twenties about speeding, I have never driven more than five miles over the speed limit, so it wasn't that hard to just know where the five mph were and not think about it. Now that I drive over an hour to work and travel in PA to do so, I have adapted a little of the "psyco" PA driving habits and started driving more than 5 mph over the speed limit. While I use that same mentality that as long as there are other drivers going faster than me, and there are, then I should be fine, I still am a little paranoid about my speed.

 

same problem here.

exactly 3 mph all the time...also according to my GPS, and those police/construction chronographs..

i heard there was a way to calibrate it somewhere..

 

I called my local dealer about it and they said there was nothing they could do except replace the speedometer.

 

Did the dealer guarantee that the new speedometer would read 3 mph slower than the current one?