I wonder if anyone has experience getting an inaccurate speedometer recalibrated. Can the job be done with precise results?

The speedo on my 96 Max reads too high by about 6 percent, so when it reads 60 the actual speed is only about 55. (The rims are stock and the tire size is correct.) I find it irritating and would be willing to have a specialty shop fix it, but I would like to know if there are pitfalls in getting this done.

Perhaps the problem is not with the speedometer head. On older cars of various makes the speedometer was driven by a mechanical cable attached to the transmission, so the problem would be either the cable or the speedo head. But I have seen some posts that imply the 4th gen speedometer depends on an electronic speed sensor. If so, could it be that the speed sensor is at fault and may also be sending inaccurate readings to the ECU?

I'd appreciate some expert guidance.

 

I'd say the speed sensor would be more at fault than the actual speedometer.

 

Anyone else have an idea? BTW where is the relevant speed sensor located?

 

How do you know the speedometer is not accurate? I haven't seen a mileage check in years.

 

I've checked the speedometer by stopwatch timing over various marked distances on California Interstate Highways. There are mile and even half-mile markers along many long stretches of these highways. Realizing that the position of these markers may not be perfectly accurate, I have tried using distances of various mileages, e.g., 3, 5, 10, and even longer. I've run speed tests at various highway speeds between 55 and 75 mph to see if the percentage error was any different. Maintaining speed can be difficult, but over many tests on long boring drives I found results consistent within plus or minus 1%. If the results weren't so consistent I'd be willing to believe the mile markers were not reliable, but in fact the tests come out very close to one another. I've done this with all my other cars and have never found as large an error (about 6% high) as I have with my 96 Maxima.

Another check is the mobile stations the cops set up to measure your vehicle speed by radar detector and display the speed on a large digital sign. Driving my other cars over the years, I have found that these displays almost always match the speedometer reading. This has been consistent for speeds ranging from 20 to 45 mph. This 96 Maxima speedometer reads so high that the error (compared to the radar displays) is evident even at relatively low speeds, although it's nearly impossible to read exactly what the mph error is by glancing at the dashboard in city traffic.

I remember years ago there were a few speedometer check postings scattered around California highways where there were signs announcing the upcoming check markers. Usually they were no more than 2 or three miles long and if you weren't ready or if the traffic didn't cooperate, you'd drive past before getting a useful timing. I don't see those speedometer checks anymore.

 

You can use a handheldp GPS receiver to verify your actual speed against the meter.

 

That would be way too easy.......

 

My handheld GPS indicates a similar speedo inaccuracy.

 

I have the same issue with my maxima, only it's about a 9-10% error, reading too high. Could always change tire size to compensate.

 

In my shop how we check speedo's is: first test drive a known good speedo write down the milage. drive exactly 1 mile. note your start and finish points exactly. then drive your max the same distance see if you drove exactly 1 mile on your odometer.at the same distance if you read.8 of a mile then your 2/10 slow. On american cars the gear is replaceable to correct speedo problems. But I'm not sure if max's have differant size gears for the speed sensor

 

well if you know exactly how off it is you could remove your needle and calibrate it a little lower than actual

when i removed my needles the first time i was soo terified i was gonna have my speed be off and get myself a ticket so i had my friend drive behind be and put his arm out the window at 25mph increments to make sure i calibrated it correclty

so if you set the needle counterclockwise a few degrees past the calibration point this could solve your problem... but many ppl are scared of messing with their gages so this may not be an option for you

keep us posted on how you do correct it tho as im interested

 

My Uniden radar detector had GPS built in(The gps in radar detector caculated speed), past 120KM/hr it wouldn't be accurate... so not sure how accurate it is even at lower speeds.