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LutzAuto Speedo Correction Device Issues

The incremental calibration is really nice - so much easier than "hoping" with a speedo gear, and having to get a new gear if something between the transmission and ground changes in the future.

TL;DR - I've been happy with the device, though I had to replace it, and I discovered (because of the device) that getting the speedometer to be accurate is NOT what we should all be shooting for!

In May, I installed a LutzAuto Toyota 3-wire Speedometer Correction Device. It was an easy process, and I was looking forward to finally having my speedometer and odometer be 100% accurate. Imagine my surprise then, when they were not!

As I noted in the install, it's easy to calibrate the device in 0.5% increments, and knowing that my speedometer was off (high) by 6%, I made sure the device was "reset" and then pressed the "down" button 12 times, resulting in my speedometer being 100% accurate (compared to a multitude of GPS devices that I compared it against).

Sure that calculating my gas mileage would be so much easier now - since I wouldn't have to adjust the miles travelled in the - you can imagine my surprise when I was watching the odometer as I passed mile markers on the freeway and noticed that my odometer was ticking off miles much more slowly than the mile markers indicated. After a bit of long-range experimentation - a 100-mile stretch of GPS-and-mile-marker highway - I determined that my odometer was off (low) by approximately 4.5%, though the speedometer was spot on.

That meant that I had a decision to make: calibrate the device so that the speedometer was correct OR calibrate it so the odometer was correct, because it's impossible to make them both accurate at the same time. I'll get into why in just a second, but for me, the odometer is much more important. Luckily, the LutzAuto device is easy to calibrate, so I slid under the Tacoma, pressed the "up" calibration button 9 times (4.5% change from its current calibration) and boom, my odometer is now 100% accurate.

So, why the discrepancy? I believe this is a conscious decision by Toyota. From the factory, Toyota tries to ensure that when the odometer is accurate, that the speedometer will always read slightly higher than the actual speed that the vehicle is traveling. This is a CYA (cover your ass) strategy - essentially, it ensures that when the speedometer implies the vehicle is travelling at the posted speed limit, it's actually travelling at that speed or slightly slower, reducing their liability in court, should the speedometer reading be called into question.

At any rate, it means that calibration of the speedometer is not as important as I once thought, but that calibration of the odometer is the key. The LutzAuto device does both, so it's still the best way to perform that calibration (as compared to speedo gears, etc.)

Since the install, it should also note that I had had to replace the LutzAuto device when it started malfunctioning. I'd be driving along at a consistent speed/RPM, and the speedometer would suddenly begin to jump all over the place. After a couple emails to Bryan (the owner/creator), we weren't able to figure out the issue and he sent me a new device (and a shipping label to return the original). I installed the replacement and it's been working well ever since. Great customer service, as well!

I have to admit, this was sort of fun, even if I wanted it fixed.


Update: January 2024

The new LutzAuto speedo correction device is demonstrating the same jumpy speedometer behavior as the first one. I think is has to do with the connection between the device and the speedo gear, and for now, I am removing the device. Bummer.


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