I am resetting TPSM but light remains on (all 4 tires are 50psi)

No tape, thank you. I bask in the baleful light of the TPMS sensor every winter, with my snows tires (no sensors).

Ah, I can kinda see that. Maybe. No, I would just sell it as-is, tell the guy the story, IF he notes it, and be about as flexible on the price as the cost to remedy. Again, IF pressed.

I just can't get too excited about TPMS sensors, lol.

 

Maybe im not reading these posts correctly but the tpm switch on steering column is for setting the pressure you want the low tire pressure to come on at so if you press and hold to get the three flashes while your tires are at the desired pressure then your warning light will come on as soon as pressure dips.

 

... but the light also stays one when it can't get readings from one or more sensors at all, whether it be a bad sensor, dead sensor battery, radio reception or interference problem, or a wheel without sensor at all.

Some tires call this out as the max cold pressure, before any road or day heating occurs. The later heating is included in their built-in safety margin, which should also include margin for common elevation changes (High elevation -> lower ambient air pressure -> higher internal gauge (not absolute) pressure).

 

Yes, but you pump your tires up to the correct pressure then use the switch to calibrate. This sets the warning light pressure to a few PSI below.the current pressure.

 

$240 (excluding tire cost) for 4 TPMS is a lot cheaper than ~$800 I spent on 4 TPMS on my old HCH. But if I knew what I know now about TPMS, I suggest option 4: Buy cheap external TPMS at Amazon around ~$40, and know exactly each tire presser is all the time while you are driving.

That said, I can see why you wanted to take care of TPMS light issue before selling your car.

 

Maybe just hearsay, but I've heard a 25% drop below set pressure is needed. Normally. In other words, if set pressure is 40 they'll alert at 30. That said, I've had mine go off AT the set pressure. A one time bug I think.

 

The sensors measure both tire pressure and temperature. And yes when the battery’s run out you get the light on no matter if you try to reset it.

 

I think you're right, it sounds like hearsay. It wouldn't make sense to use a percentage. It would be a hard 3-5 PSI at most.

 

More hearsay?

We could put this to bed, by just testing. Set all four tires to the same pressure, do the TPMS reset, then with the car fully on, start dropping pressure in one tire, say a couple of pounds at a time, wait a minute or two, repeat. See how much pressure drop is needed to to set off the light.

 

No, just a WAG based on what seems reasonable.

Yes you could. I couldn't, I don't have TPMS, thank goodness, but would happily do so, if I did.

 

I don't see why a fixed hard number makes any more sense than a percentage. Microprocessors have enough math processing capacity to handle either.

 

Plus don’t forget, the sensors measure tire temperature as well as pressure.

 

I never got around to fiddling with the reset to see if I could adjust the alarm setting upwards...I think there is a default value around 26 or 26.5 psia as the base case minimum.

If its percent basis then maybe it is % x (P+14.7) but then 25% sounds too high

 

Techstream can read the actual tire pressure that will trigger the warning light.