How To Fix A Misreading Speedometer
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 Published On May 3, 2017

How To Correct A Speedometer - Honda S2000 - Speedo Corrector
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Fixing the speedometer on my Honda S2000, which as you can see clearly reads too high. While traveling at a GPS verified speed of about 80 to 81 miles per hour, you can see the car’s speedometer is reading 87 miles per hour, significantly higher than the actual speed. This is a result of changing the final drive gearing in my S2000, but you could also have a speedometer reading incorrectly from putting on different tires or wheel sizes. To correct this, first you need to know how much your speedometer is off by. You want to travel at the highest legal speed you can near you, so that you can have an accurate percentage difference. In my case, driving at about 81 miles per hour shows a speed of 87 mph, so my car is reading about 7.4% high.

Next I’ve purchased a Yellow Box correction kit. These can be used for many different makes and models of vehicles, simply splicing into the speed signal wire, or by using a plug and play kit they provide, also available for many different brands. The first thing we need to do for the install is lift the front of the car up onto jack stands. The speed sensor for the speedometer is on the transmission for the S2000, so we’ll need access to it. Once underneath the car, unplug the sensor from the transmission, and plug in the new harness. There will be plenty of wire length for the Yellow Box to plug in, so at this point I pulled the connector out from under the vehicle to program it. Then plug in the Yellow Box.

Turn your ignition to accessory mode, and you should see some lights flashing on the Yellow Box. Once powered, the box will tell you what the current correction factor is, by flashing the red light. Short flashes represent a count of one each, and long flashes represent zero. In this case we have 1 flash, then four long flashes, meaning 1 0 0 0 0, or 100.00% correction factor.

My S2000 is reading about 7.4% high, so we want a correction factor of 107.40%. To program the box, hold both buttons for about 5 seconds, until both green and red lights flash. Now, by pressing the plus button, the correction factor will go up by 0.1 percent. Pressing the plus button 74 times will give us our 107.4% correction factor. You can also hold the button to speed this up.

After you’ve programmed it, wait for both lights to flash. This informs you the setting has been saved. Turn the car ignition off, and then turn it back on to check that the setting is correct. Once powered, the device automatically reads the current setting to you.

I’m simply choosing to zip-tie the Yellow Box for now, directly beside the transmission housing. The device comes with a 10 year warranty and is weatherproof, heatproof, and vibration proof, but make sure you don’t place it near your exhaust or extreme heat sources. With the device in place, it’s time for a test drive. As you can see the car now reads much closer to the actual speed, and is reading just slightly conservatively high, which I’m fine with. You could choose to fine tune at this point if you prefer.

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