How Accurate is the TPMS?

I bought a new tire pressure gauge that is supposed to be ANSI certified accurate. The TPMS is reading 3 pounds higher than the gauge. Gauge says 30, TPMS says 33. Anyone know if the TPMS is accurate? I think I will double check readings against 2nd gauge.

 

They're usually pretty accurate, but the Tacoma doesn't give a read out until you're driving, so there's a very good chance your comparing cold readings to warm readings. Moving tires can heat up very quickly.

 

Definitely compare. All that I really know is that the ECU gets live readings of pressure down to the 100th of a psi and temperature. That doesn't mean that they are accurate though.


A 3psi difference is significant.

 

Mine are not accurate at all. I constantly get 3-5 psi lower than my gauges.

 

In my experience tpms are not a good/accurate tool for checking the actual tire pressure, they are good for comparing one wheel to the other to see if one is much lower then the others
I have a digital guage at work and I can set two trucks tires at 40psi but they will read slightly different from each other even though the same tool was used to reach the same pressure at the same time.

 

TPMS can be designed quite sloppy to save money, because federal regs only require the TPMS to detect a tire that has fallen 25% below the doorjamb sticker pressure within 20 minutes. I would trust your gauge.
https://one.nhtsa.gov/cars/rules/rulings/tpmsfinalrule.6/tpmsfinalrule.6.html#IV_1

 

I have two digital gauges from Home Depot. Both read 30psi cold. My dash on my 2018 and 2020 read 29-31 cold.
Seems to me they are accurate (or the Husky brand gauges are equally inaccurate).

 

They are fairly precise but not necessarily accurate. Manufacturing and material tolerance always create gain variations when it comes to sensors like this. They target a particular gain but unless they are individually tested you do not know what it is. I'm pretty sure Toyota or their supplier does not calibrate every sensor that comes off the line. They basically just fall within an allowable range for a batch and end up on your truck. I do see the 3rd gen sensors as fairly accurate compared to my manual pressure checks, but they are not exact and you shouldn't expect them to be. But if they're off by some amount you can expect them to remain off by that same amount.

Having said that, I air up with an equalizing setup and while the sensors may be slightly off from the measured pressure, they do match each other very well.

 

If you turn on your truck and wait a couple minutes it will give you a readout before you departure...

I’ll do it like that so I get a cold reading.

no need to drive truck to get read out.

 

When I bought new wheels, I had aftermarket sensors installed. Anecdotal but they seem more accurate than OEM. I run my tires on the hard side... 36 psi. Recently I noticed they were down to 33~ (colder weather I suppose) so I ran up to Discount Tires and asked for 36 psi please. After the nice attendant fired them up I started the truck and they still read 33. Drove away and after about a mile, they magically moved to exactly 36 psi.

 

TPMS is very accurate but it's hard to compare to a gauge because... motion and friction and sampling rate. TPMS does not sample continuously, it samples at a set time, like maybe once a minute or so except if it senses a pressure drop.
Best way to check is to drive your vehicle around for 10 minutes, check the TPMs and immediately check using gauge. ANSI certified does not mean crap.

 

High elevation causes difference between TMPS vs gauge readings.

 

Not quite. Plug techstream and youll get the reading on the vehicle...

 

As above. TPMS are very accurate, problem arises at altitude where the atmosphere pressure is different. Tire gauge will tell you difference between outside pressure and inside tire pressure, TPMS will tell you the actual tire pressure using sea level as the base. There are pros and cons to each way of measuring, so take you pick as to what one you want to use.

 

The TPMS transmit 24/7/365. My truck hasn’t moved in 3 days, look at the date of the last pressure and temp readings (yes they also transmit tire temperature) and factory spare on my truck at least came with TPMS.

 

Same here. My TPMS readings are typically 2-3 PSI lower than all of my gauges.

 

The TPMS ECU is getting continuous data. I've seen it in TS. How long it takes the center display to put up the first reading and how often it updates is different like you noted.

 

I thought I read in the manual to set tires to recommended pressures on the door sticker before doing a TPMS reset. I figured that would ‘calibrate’ what the ECU is seeing. Mine were off a bit until I did this and the numbers now match my gauge (Blu-point). Im probably crazy... I live at sea level.

 

Good point. That may work. I wonder if @Jeff Lange knows?

He had the good info about how the sensor discover wheel position. The ECU measures signal strength from the antenna location. That's pretty wild.

 

I’m gonna try the reset. Good idea!!