Here's what likely happened:

It was cold enough when your wife left that the tires were in fact that low, as she drove, they heated up and pressures increased as happens with any tire.
This is why pressures are supposed to be checked cold and inflated to appropriate pressures cold.

 

I generally agree, but a reading of over 1-4 PSI cold to warm is normal. Anything beyond that and I would say they are reading incorrectly. If I understand the OP correctly, the dash reading was 30 PSI when the gauge readings were 38-39 PSI. That is outside the normal IMO.

To the OP, I believe the low pressure warning is modifiable with AlfaOBD, if you are comfortable knowing the variance of the OEM TPMS is off, you can lower the threshold.

 

Driving the 3/4 at 54F mile that her errand entailed seems terribly unlikely to cause the pressures to increase by 9 PSI. Also, I edited my original post to fix the typo about the LR pressure.

This is not the first time that I've seen the pressure difference between the TPMS indication and known good gauges. It's just the first time I have asked about it.

 

AlfaOBD. Which means a trip to the dealer. Not a big deal. Something to add to the next visit.

Here in this part of Arizona, "cold inflation" is a moving target. Checking tire pressure at 0600 can be at 32F or 109F. 35 PSIG at those variations means different things.

Many years ago, I was responsible for an equipment trailer that ran LT245/75-16E tires. We normally kept those tires at 70 PSIG in a garage climate-controlled to 85F. There came a day when the garage needed work, so we moved the trailer to a covered spot where the ambient temperature was 112F. If I recall correctly, that 70 PSIG rose to about 80 PSIG over the space of six hours.

 

AlfaOBD. Which means a trip to the dealer. Not a big deal. Something to add to the next visit.

Here in this part of Arizona, "cold inflation" is a moving target. Checking tire pressure at 0600 can be at 32F or 109F. 35 PSIG at those variations means different things.

Many years ago, I was responsible for an equipment trailer that ran LT245/75-16E tires. We normally kept those tires at 70 PSIG in a garage climate-controlled to 85F. There came a day when the garage needed work, so we moved the trailer to a covered spot where the ambient temperature was 112F. If I recall correctly, that 70 PSIG rose to about 80 PSIG over the space of six hours.

Purchasing AlfaOBD and a compatible adapter should put you right at the cost or under of a dealer visit. Many dealers charge their minimum rate for these things, I think my dealership is up to $169 minimum to look at a vehicle for a non-warranty issue. Just food for thought...might even be a forum member near you willing to help that already has AlfaOBD!

 

I'm looking for suggestions for AlfaOBD devices. Stand-alone or Android-connecting. Based on what I have seen, I am willing to pay up to maybe $500 if the device will also communicate with a Subaru.

 

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I'm looking for suggestions for AlfaOBD devices. Stand-alone or Android-connecting. Based on what I have seen, I am willing to pay up to maybe $500 if the device will also communicate with a Subaru.

Any android device will do, I recommend Android over Windows as it seems to have less issues with compatibility and is more portable. If you don't have an Android phone, you can use an old phone or tablet (or a friends who is willing to part with it). I recommend OBDLink MX+ (just missed the holiday sale which is about the only time they can be had for under $100) as it is the most compatible and feature rich OBDII adapter but you can start with cheap OBDII readers for around $15 that will work for much of the programming that can be done with AlfaOBD. If your vehicle is a 2018+ model year, you will need a security gateway module bypass adapter as well.

AlfaOBD

AlfaOBD - Apps on Google Play

AlfaOBD software for Fiat Group cars native diagnostic

play.google.com

OBD Link MX+

Amazon.com

SGM Bypass

Amazon.com: PARANNIC Security Bypass Cable OBD2 Adaptor for Chrysler 12+8 Programming Cable Connector for Autel DS808 Maxisys for Autel MS905 MS906 MS906BT MS906S MS908 MS908S Pro Maxisys Elite : Automotive

Buy PARANNIC Security Bypass Cable OBD2 Adaptor for Chrysler 12+8 Programming Cable Connector for Autel DS808 Maxisys for Autel MS905 MS906 MS906BT MS906S MS908 MS908S Pro Maxisys Elite: Code Readers & Scan Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Cheaper OBDII adapter that worked for my 2014 Ram

Amazon.com: Veepeak Mini Bluetooth OBD II Scanner for Android ONLY, Auto Check Engine Light Code Reader Car Diagnostic Scan Tool : Automotive

Buy Veepeak Mini Bluetooth OBD II Scanner for Android ONLY, Auto Check Engine Light Code Reader Car Diagnostic Scan Tool: Code Readers & Scan Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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The issue with cheaper OBDII adapters is that sometimes other adapters have to be used in conjunction with them to properly communicate with certain modules on the CANBUS. The OBDLink MX + intelligently switches these pins for you logically prior to connecting to specific modules. In addition, some OBDII adapters have a baudrate that is too slow to successfully connect to some modules and make changes. That being said, the cheap one Iinked to allowed me to change many settings on my 2014 Ram and even program mileage/engine hours in the odometer of an upgraded replacement cluster.

AlfaOBD works across all Stellantis vehicles and is not tied to a specific VIN. One license essentially has unlimited uses and is tied to your Google Play account.

 

Our Pacifica is a 2019, so it looks like a security module bypass will be necessary. Thanks for the ideas.