Tpms and Jscan - is there an upper limit?

[RollingThunder]

New tires put on and pressures were 35 psi. Jscan said my max load value was set at a default of 36, but I did not get a TPMS warning light. So just to check functionality, I increased the max load value to 45 with Jscan thinking my 35 psi would throw a warning light, but nothing. There are several threads about lowering the Jscan values to get rid of the warning, but not the other way. I just want to confirm my warning light will go off if I have an unexpected drop. What am I missing?

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[JT1]

The lower limit to set off the tpms alert is 29psi.. go drop a tire to 29 and see if the light comes on.. with you setting the upper to 45, you may need 46~47psi to turn the light off..

 

[RollingThunder]

Thanks. But I thought the point of the Jscan TPMS setting is to lower the threshold that sets off the light for when you air down. So I would think that if I set the value at 45, I would get a light below 45, which I don’t. Or are you saying the lower limit doesn’t really change - it’s 29, and the Jscan value is just the number needed to air up to in order to turn OFF the light triggered at 29?

My next step is to do as you suggest and just air down the tire to see if I get a light. But then I am not sure what use the Jscan values are if it doesn’t change when the light is triggered.

 

[Hootbro]

TPMS thresholds are generally around 20%-25% drop before the light will come . If your set threshold is 45 PSI as your example, then you can expect the TPMS light to come on around 34 PSI. So from 35 PSI to 44 PSI, your TPMS light will not generally come one.

Once you get the TPMS light, you will have to inflate the full 45 PSI for the TPMS light to go off.

Why would you want the reverse of a TPMS light going off when the pressure drops?

 

[RollingThunder]

Thanks. I don’t want the reverse normally. I just want to confirm the TPMS will throw a light when the pressure does drop. So rather than deflating the tire to test it, I thought I could just raise the threshold with JScan. I thought 45 would be enough to do it, but I haven’t thrown a light. So I guess I will just deflate the tire to confirm TPMS throws a light.

 

[RollingThunder]

TPMS thresholds are generally around 25% drop before the light will come . If your set threshold is 45 PSI as your example, then you can expect the TPMS light to come one around 34 PSI. So from 35 PSI to 44 PSI, your TPMS light will not generally come one.

Once you get the TPMS light, you will have to inflate the full 45 PSI for the TPMS light to go off.

Why would you want the reverse of a TPMS light going off when the pressure drops?

So if the light triggers at a percentage of threshold, that answers my main question. The number you put in with JScan is NOT the number that trips the light. It is a percentage less than that number. That could explain why I didn’t get a light at 37 psi when I set the number in JScan to 45-because it is 45 minus some percentage and not 45.

 

[Hootbro]

The number you put in with JScan is NOT the number that trips the light. It is a percentage less than that number.

You got it now.

One quirk with the latest iteration of JScan is that once you come off the factory 37 PSI setting, any setting you select now in Jscan will be in blocks of five like 35, 30, 25 PSI and etc.. I do not know if there is a way with JScan to go back to either 37 or select any other number that is not in a block of five segment.

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