Wrong speedometer reading on 98 Honda Civic EX

[DaleHuff]

I'm needing help on trouleshooting a problem with my 98 Honda Civic's speedometer reading faster than what the car is actually traveling at. I have found when moving at slower speeds, the speedometer is fairly accurate. But, as the cars speed increases the speedometer's reading becomes more inaccurate. When driving at 60 mph, the meter reads 65 mph. The wheels and tires are stock and there are no other modifications. Ive checked the speed sensor, per the haynes manual, and it appears to be working properly. But, you cant really see much with just a voltmeter. The engine check light is not on. Is it possible the sensor could be somewhat flakey and if not, is there a way to calibrate the speedometer to the sensor?

Thanks.

Dale

[dougbfresh]

Are the tires the stock size? You say the wheels are, but what about the tires?

[DaleHuff]

Originally Posted by dougbfresh

Are the tires the stock size? You say the wheels are, but what about the tires?

Yes, the tires are stock size.

Dale

[carsandcycles]

I did a Google search and it seems that Honda's have a reputation for this type of speedometer error. (Maybe other car companies too, though I also remember GM had some of the best correlation to real speed.) There seemed to be the same optomistic readings you describe by other Honda owners in the 65 to 70 mph range. I think your only recourse is to make a mental calculation adjustment as you accellerate to your final speed. There was some alluding comments that thought a 10% error factor was legally allowed, which fits your condition.

If you want to read some of the comments other people had, my Google search was simply: Honda speedometer accuracy

[dougbfresh]

Many late model cars can be "recalibrated" via the diagnostic OBD port to compensate for different wheel and tire combinations. Your local Honda dealer will probably have to do it for you.

[warped_joe]

Does it have the orginal trans. some times if it has a replacement trans from Japan, The gears can often be a little different or may have come from a car that ran on a different size tire.

On another note, there are also fixes for incorrect speed readings. You can buy a speedo healer that you install and calibrate yourself.

[olddog]

That's how Honda get such great fuel mileage and they last so long. The fuel mileage looks 10% better than it actually is, because it registers 10% more miles than it actually went.

Now to explain why the error gets larger as you go faster. At 20 MPH (with a 10% error) your actual speed is:
20 - (20 * 10% ) = 20 - 2 = 18 MPH. - not noticable

At 100 MPH your actual speed is:
100 - (100 * 10%) = 100 - 10 = 90 MPH. big error

You may find that the error is much larger like 20%.

[DaleHuff]

Thanks.

Got a scangauge and found the speed signal coming from the ECU is correct. It's the speedo reading wrong. Any way to cal the meter, besides getting a new one?

Dale

[dougbfresh]

You might be able to have to old one calibrated but why?

[FieroSpeeder]

Originally Posted by DaleHuff

But, you cant really see much with just a voltmeter. The engine check light is not on. Is it possible the sensor could be somewhat flakey and if not, is there a way to calibrate the speedometer to the sensor?

Dale

A newbie knows what he's talking about. You cant see much with a voltmeter, you need a labscope.


You need to find a guy out there that recalibrates the speedo. They use an oscilloscope and check the frequency steps at each speed and improve the accuracy by soldering in new components to compensate.