Setting TPMS Thresholds

[LAM]

Has anyone been able to set the tire pressure thresholds to 15psi or lower?

I had set mine - using jscan - to 20psi and the warning seemed to work as expected. The warning light came on when my tire pressure was around 19psi or lower.

Recently though I tried to lower the thresholds to 15psi. But now when I air down to 19psi, the pressure warning light comes on with the message ‘pressure is below 19psi, inflate tires to 15psi’. This doesn’t make sense. I tried to reset the ecu’s but I still get the warning coming on above 15psi.

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[2nd 392]

Has anyone been able to set the tire pressure thresholds to 15psi or lower?

I had set mine - using jscan - to 20psi and the warning seemed to work as expected. The warning light came on when my tire pressure was around 19psi or lower.

Recently though I tried to lower the thresholds to 15psi. But now when I air down to 19psi, the pressure warning light comes on with the message ‘pressure is below 19psi, inflate tires to 15psi’. This doesn’t make sense. I tried to reset the ecu’s but I still get the warning coming on above 15psi.

I’m surprised it went that low. Tazer only goes to 25 psi. According to them it’s the lowest that will be accepted.

 

[Ratbert]

I'm trying to figure out your use case where a warning at > 15 PSI would make sense.

If it's to detect breaking a bead then 15 PSI is way too high (IMHO). If it's to detect a flat on the road then 15 PSI is way too low (again, IMHO).

 

[LAM]

I'm trying to figure out your use case where a warning at > 15 PSI would make sense.

If it's to detect breaking a bead then 15 PSI is way too high (IMHO). If it's to detect a flat on the road then 15 PSI is way too low (again, IMHO).

In my lifetime I’ve destroyed two tires getting flats on rocky dirt roads and not noticing until the tire was shredded. If I am aired down to 19-20psi and the warning is less than that I might notice the warning light (and again I might not). If the warning light is on all the time it doesn’t help me.

On the highway I expect a change in handling and road noise if I have a flat or near flat; doesn’t really matter where the TPMS threshold is set. For me TPMS is a newfangled system.

 

[Terrymo]

I’m surprised it went that low. Tazer only goes to 25 psi. According to them it’s the lowest that will be accepted.

I thought JSCAN and Tazer would only go down to 25 psi because that’s what is “hard coded” (probably wrong terminology) by Jeep. @THAW is that correct?

 

[2nd 392]

I thought JSCAN and Tazer would only go down to 25 psi because that’s what is “hard coded” (probably wrong terminology) by Jeep. @THAW is that correct?

Someone else with JSCAN reporting would be helpful since 25 is the Tazer limit and supposedly Jeep’s limit.

 

[Terrymo]

Someone else with JSCAN reporting would be helpful since 25 is the Tazer limit and supposedly Jeep’s limit.

I have a Tazer and JSCAN but have my threshold set with Tazer

 

[2nd 392]

I have a Tazer and JSCAN but have my threshold set with Tazer

Does JSCAN say the same or different ? He claims 20 psi worked correctly with the warning at 19

 

[LAM]

The JScan app has a number of program features that may or may not do anything with the Jeep TPM programs. As far as the pressure the app can set one psi increments between 20 and 30, as well as 15psi, 10psi, and 0psi, also higher values.

 

[LAM]

Seems like it should be a simple calculation.

IF {measured pressure} < {threshold setting} THEN {warning light turns off}

From a software point of view I can’t think of a reason why {threshold setting} must be higher than 25 or any other positive number. But who’s to say what is in the mind of a Jeep programmer. Maybe they do their calculations in Pascals instead of psi, then convert later.

 

[Ratbert]

Seems like it should be a simple calculation.

IF {measured pressure} < {threshold setting} THEN {warning light turns off}

From a software point of view I can’t think of a reason why {threshold setting} must be higher than 25 or any other positive number. But who’s to say what is in the mind of a Jeep programmer. Maybe they do their calculations in Pascals instead of psi, then convert later.

Lawyers could have been involved.

 

[Roky]

I just turn the TMPS off with Tazer then air down, I don't need it on the trail, (ymmv). Air up when getting off the trail, turn it back on….I have it set to the lowest 25psi threshold……. This is the best way for me, until they come out with a better mouse trap…

 

[Terrymo]

Does JSCAN say the same or different ? He claims 20 psi worked correctly with the warning at 19

JSCAN says this but has also said other things that turned about to not work in the past. Maybe I’ll check it out this weekend.

 

[LAM]

There are a lot of “adaptions” in the jscan app which aren’t particularly well documented and/or which don’t apply to particular Jeep years and models. I’m always scared of screwing up something big time if I change something. In fact I decided even not to update my tire size (just a small change) because of all the steps involved, especially that restart ecu’s command. The last time I did that a few error codes came on, but they luckily went away when I drove around a while.

Other than that it’s a lot of fun playing with Jeep electronics, risk mixed with mystery.

 

[THAW]

I thought JSCAN and Tazer would only go down to 25 psi because that’s what is “hard coded” (probably wrong terminology) by Jeep. @THAW is that correct?

I used my Tazer to lower the TPMS threshold, so I don't know much about the JScan implementation. Looks like you and @LAM covered the instructions and the available settings.

Maybe I'll try testing the settings to see how it works.

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