97 LX450 Speedometer always wrong

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SHIfTHEAD

SHIfTHEAD

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I've searched but can't find a thread on this specific issue. The problem is that the speedometer is always reading too low. It's consistently wrong, as in 45 is always 55 for example. My first thought is that the speed sensor must be bad, but the thing that throws me off is that the odometer is accurate. So does the odometer use the same sensor as the speedometer? If so then the sensor must be good and the speedometer stepper motor must be off. Or I am wondering it the circuitry feeding the stepper is bad? Perhaps there is a fried component not converting the signal correctly?

Any thoughts?
 
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Nemesis1207

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There's only one speed sensor signal feeding the cluster that drives both the speedometer and the odometer. If the two really are out of sync you have a fault in the cluster. Are you 100% sure the two are reporting differently though? The easy explanation for the speedometer reading wrong is changing tyre sizes without making adjustments.
 
SHIfTHEAD

SHIfTHEAD

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Thanks for your reply. So, I've used GPS to measure speed and distance and the two are always out of sync with the odometer being spot on always. I also have an LX470 whose speedometer is wonky, but it's erratic in nature. About 75% of the time it's correct and then it just starts making sh1t up. However in this case the speed is always too low, which leads me to think the issue is in the circuitry on the speedometer board. And as you have confirmed the two use the same signal I can move on from looking external to the gauge cluster. I know that the 80's are somewhat prone to board issues as I've found many posts about bad speedometers. But in all those cases it was either working or not. So I suspect that what happens is that the board converts the 0-11v signal from the speed sensor to something the stepper motor uses, and just guessing here, my board is midway through the fried circuit board death and thus the impedance has increased on that trace on the board. This increased impedance lowers the overall voltage to the motor and thus it reads low all the time. This is actually good news as I don't need to get a speed sensor I just need to focus on the speedometer itself. And worst case scenario I will need a new one or send this one off to get it fixed if I can't do it myself. But having seen this video, I believe I have a course of action and might be able to fix it myself.
 
SHIfTHEAD

SHIfTHEAD

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I'll triple check, but I believe they are the stock 31" tires on it right now. Also, using tiresize.com/comparison I would need to increase the diameter 20% to see a 10mph drop. The plan right now is to pull the cluster tomorrow and check the board traces. I hope I'll find a copper trace that is on its last leg and can solder a jumper to carry the current in it's place.
 
Dirt Ferguson

Dirt Ferguson

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How did you figure out your speedo was off, to begin with?
 
SHIfTHEAD

SHIfTHEAD

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It's off enough that you notice it, so I pulled out my phone and checked my GPS speed. So if I'm showing 44-45mph on the Speedo and I'm actually driving 57-58, that enough that you'd probably notice it.
 
LandLocked93

LandLocked93

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I don't see the problem.
Everything sounds nominal...it's showing how fast you aren't going.
 

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