[wanderer54]

I have a 2016 and have never really had a whole lot of faith in the tire pressures displayed on the DIC or through the app on my phone.
I used two high end tire pressure checkers the other day and all 4 tires showed either 35.0 or 35.5 psi. The DIC and the app showed 3 tires with 37 and one with 38 psi.
This was with the tires cold and not yet driven in the morning. Anyone with similar experience or insights?
Thanks

 

[jguerdat]

I've found that a brief drive sometimes is needed to normalize the TPMS readings - they'll read one thing when starting the car but a mile down the road will change to what I expect. You might wanna try that next.

I also had an issue over last summer where my analog tire pressure gauge read one thing but TPMS read about 2.5 PSI lower. I haven't bought a new gauge yet but based on use of other equipment's gauges I'm 99.999% sure it's the gauge at fault.

 

[wanderer54]

Thanks for the reply jguerdat. So your TPM reads lower than the independent gauges. That is interesting. I have checked and compared the pressures later in the day after running some errands and the DIC still shows higher psi which is to be expected after driving and warming up the tires....rises to around 39 or even 40 psi, while my two gauges indicate 37 psi. Perhaps a relearn on the TPM system? Don't know. Just brainstorming.

 

[BoilerUP]

Pretty darn close, within 1psi of a digital gauge.

 

[tta1456]

Remember, the TPMS sensors are not always actively transmitting to the vehicle to conserve their battery life, so the pressures displayed on the dash may be stale (or even from when you shut the car off after your previous drive) as if the vehicle isn't moving the sensors are in stationary/standby mode. They have internal accelerometers to sense when the vehicle is moving, and when the vehicle isn't moving the TPMS sensors send only infrequent pressure updates to the vehicle to conserve sensor battery life.

If you're concerned one sensor may be off, easiest way to verify the TPMS reading is current is to start and drive the car for at least 30-60 seconds and note the TPMS pressure on the dash right when you stop the car and then immediately check tire pressures with a known good tire gauge.

They'll also go "active" if they detect a 1.2 psi pressure change in 30 seconds, so you could turn the ignition on and manually and slowly air the tire down say 5 psi, then fill it back up, and compare the reading on the dash to your gauge (this is also how you do a TPMS relearn after a tire rotation or new sensor install without an activation tool.)

Remember, the TPMS sensors are more for leak detection and gross out of range tire pressure checks than anything else, so as long as they can reliably track and report a drop in pressure or tell you if your tires are way overinflated or underflated they're doing their job-- it's the old "accuracy vs precision" scenario. Even if the absolute pressure reading is 2psi off compared to a known good gauge, as long as the TPMS sensor can detect a pressure drop beyond a certain threshold over a certain period of time to detect a leak while driving, and show a gross overfilled or underfilled deviation from the recommended filling pressure (usually around +/- 5 psi before it alerts) it's fulfilling its design function for safety and leak detection. They don't need to be accurate to 0.1psi.

 

[BKC1]

I found that the ATS-V TPMS are inaccurate on the OEM wheels (reading 37-38 PSI vs. calibrated gauge reading 35 PSI), but the exact same model TPMS sensors on larger aftermarket wheels are within ±0.5 PSI of the gauge.

I have a lot of older TPMS on other GM vehicles and these are the only ones that have the problem. I haven't tried transferring the factory-included OEM sensors to the aftermarket wheels to see if the problem follows the sensors or if there's some weird interaction going on between the TPMS and the OEM wheels.

TLDR: I have the same exact problem as Wanderer, but only on the TPMS sensors that were originally included on the 2018 ATS-V. The same P/N TPMS purchased a year later for my aftermarket wheels don't exhibit the problem.

 

[jguerdat]

I have 2 sets of wheels - OEM and Tirerack cheapies for winter. Both sets of sensors provide the same readings, at least within the 1 PSI display of pressures. My now-gone Fiat 500 Abarth was more of a suggestion, rather as @tta1456 suggests. I've used the dash display to monitor pressure changes for autocross since I bought the car new. Last summer's sudden change was unexpected and I still need to get a new gauge.

 

[max2]

Remember, the TPMS sensors are not always actively transmitting to the vehicle to conserve their battery life, so the pressures displayed on the dash may be stale (or even from when you shut the car off after your previous drive) as if the vehicle isn't moving the sensors are in stationary/standby mode. They have internal accelerometers to sense when the vehicle is moving, and when the vehicle isn't moving the TPMS sensors send only infrequent pressure updates to the vehicle to conserve sensor battery life.

If you're concerned one sensor may be off, easiest way to verify the TPMS reading is current is to start and drive the car for at least 30-60 seconds and note the TPMS pressure on the dash right when you stop the car and then immediately check tire pressures with a known good tire gauge.

They'll also go "active" if they detect a 1.2 psi pressure change in 30 seconds, so you could turn the ignition on and manually and slowly air the tire down say 5 psi, then fill it back up, and compare the reading on the dash to your gauge (this is also how you do a TPMS relearn after a tire rotation or new sensor install without an activation tool.)

Remember, the TPMS sensors are more for leak detection and gross out of range tire pressure checks than anything else, so as long as they can reliably track and report a drop in pressure or tell you if your tires are way overinflated or underflated they're doing their job-- it's the old "accuracy vs precision" scenario. Even if the absolute pressure reading is 2psi off compared to a known good gauge, as long as the TPMS sensor can detect a pressure drop beyond a certain threshold over a certain period of time to detect a leak while driving, and show a gross overfilled or underfilled deviation from the recommended filling pressure (usually around +/- 5 psi before it alerts) it's fulfilling its design function for safety and leak detection. They don't need to be accurate to 0.1psi.

you are correct about the sensors needing a refresh, but i have shut the car off at night in the winter @38 psi and checked the app in the morning cold and it would show 35 psi...but yes, upon adding air the car must be driven to refresh the tpm ..i use a digital gauge, but use the cars numbers as my guide, they are usually the same.

 

[max2]

I've found that a brief drive sometimes is needed to normalize the TPMS readings - they'll read one thing when starting the car but a mile down the road will change to what I expect. You might wanna try that next.

I also had an issue over last summer where my analog tire pressure gauge read one thing but TPMS read about 2.5 PSI lower. I haven't bought a new gauge yet but based on use of other equipment's gauges I'm 99.999% sure it's the gauge at fault.

whatever the feel works better ..i use the cars system and it's 38 psi hot which i feel gives me the best ride and go by that as a guide because i could lose the gauge or it could break..

 

[tta1456]

you are correct about the sensors needing a refresh, but i have shut the car off at night in the winter @38 psi and checked the app in the morning cold and it would show 35 psi...but yes, upon adding air the car must be driven to refresh the tpm ..i use a digital gauge, but use the cars numbers as my guide, they are usually the same.

Correct, the sensors still update the BCM when the car is turned off (also for OnStar polling), but the update rate is only occasional... I'm not sure how often the TPMS sensors update when the car is off and parked, but it certainly isn't updated as often as when the car is rolling and the sensors are in active mode.

A couple years ago I got a text message from Onstar in the middle of the night that the left rear tire was low... funny, because it was OK when I got home and I never got a TPMS alert on the dash while driving home. OnStar was right though, went out to the garage and it was down 9 psi because it had a nail in it. Nice to get that update and get a jack under it before it went totally flat.

 

[wanderer54]

Thanks guys for all the anecdotal experiences and knowledge. I appreciate it. I tend to be somewhat OCD with car care but now that I have the knowledge base on these TPM units I will not make myself crazy about their readings. Thanks again!

 

[ELDORADO2K]

I tend to be somewhat OCD with car care

I don’t blame you, I’m the same way. I recently bought a new digital tire pressure gauge to replace a similar 1 that quit working. Then I bought a new tire inflator from the same brand but they both give me different readings that are off by 2 psi. and it bugs me to the point where I feel like getting another digital gauge from a different brand [like the 1 I had before] to settle the score and figure out which gauge is accurate.

2 psi. is enough to bug me. I like my tire pressure to remain where I set it. That’s the whole reason I bought these damn gauges to begin with.

 

[wanderer54]

Hey Eldorado...We seem to think the same way. My gauge came from Giots and it was not cheap! I probably trust it more than the TPM sensors. BTW. ......I had a 2002 Eldorado ETC up until a couple of years ago when I traded it for the ATS-V. Loved the car, but the security system was a nightmare. Never knew when it would start and nobody could find the problem. The Pass Key system is the worst!

 

[ELDORADO2K]

Hey Eldorado...We seem to think the same way. My gauge came from Giots and it was not cheap! I probably trust it more than the TPM sensors. BTW. ......I had a 2002 Eldorado ETC up until a couple of years ago when I traded it for the ATS-V. Loved the car, but the security system was a nightmare. Never knew when it would start and nobody could find the problem. The Pass Key system is the worst!

Here's the digital gauge & inflator that I picked up off Amazon. Brand is Astrol AI

Sucks to hear the pass key turned into such a problem. I remember the only thing I had to deal with was the pellet became loose on 1 of my keys and would cause the warning message to flash on the dash. I made it the spare key and fortunately never had to deal with it again.

 

[wanderer54]

Here's the digital gauge & inflator that I picked up off Amazon. Brand is Astrol AI

Sucks to hear the pass key turned into such a problem. I remember the only thing I had to deal with was the pellet became loose on 1 of my keys and would cause the warning message to flash on the dash. I made it the spare key and fortunately never had to deal with it again.

 

[wanderer54]

Yeah, if only it was that simple. If the ambient temperature was above 70, if would usually start. But below that, completely dead. It turned into a very expensive thermometer. Some hypothesized that it was an intermittent ground problem. So many grounding points. Impossible to isolate the offending one. BCM replaced, did not matter, ignition switch replaced did not matter, new keys, did not matter. It was a shame to have to get rid of her. GM had a long history of Pass Key security system complaints. At least yours was simple to solve.

 

[vb48]

Here's the digital gauge & inflator that I picked up off Amazon. Brand is Astrol AI

Sucks to hear the pass key turned into such a problem. I remember the only thing I had to deal with was the pellet became loose on 1 of my keys and would cause the warning message to flash on the dash. I made it the spare key and fortunately never had to deal with it again.

What is the model number and how long ago did you buy from Amazon

 

[ELDORADO2K]

Some hypothesized that it was an intermittent ground problem. So many grounding points. Impossible to isolate the offending one.

Iirc that’s similar to what killed my 92’ Eldorado. I sent it to a couple different mechanics but they couldn’t quite figure out exactly what was going on with it and even though I had plenty of money to just have the dealer fix it, I got to the point where I had gotten tired of the same car and couldn’t justify throwing that much money into it when I kinda wanted to buy a different Cadillac, a sedan.

What is the model number and how long ago did you buy from Amazon

The model # is on the 2nd page. I paid $45
The main reason I chose this 1 is because it allows you to connect it directly to an outlet/extension cord and not only through the cars 12v plug. It has the option for both, but I prefer to plug it into an outlet instead of using the car.

 

[vb48]

Iirc that’s similar to what killed my 92’ Eldorado. I sent it to a couple different mechanics but they couldn’t quite figure out exactly what was going on with it and even though I had plenty of money to just have the dealer fix it, I got to the point where I had gotten tired of the same car and couldn’t justify throwing that much money into it when I kinda wanted to buy a different Cadillac, a sedan.



The model # is on the 2nd page. I paid $45
The main reason I chose this 1 is because it allows you to connect it directly to an outlet/extension cord and not only through the cars 12v plug. It has the option for both, but I prefer to plug it into an outlet instead of using the car.

thank you Sir

 

[tta1456]

Thanks guys for all the anecdotal experiences and knowledge. I appreciate it. I tend to be somewhat OCD with car care but now that I have the knowledge base on these TPM units I will not make myself crazy about their readings. Thanks again!

Remember, your tire pressure OCD isn't completely satisfied unless you send your tire pressure gauges off to a NIST-traceable calibration lab at least yearly to be checked and calibrated so you can be 100% sure you are putting exactly 35psi in your tires. Can't expect to get your garage ISO 9001 certified without a documented measuring instrument calibration and recall procedure on file for the auditors to verify.