My car is almost three years old, and all during that time I've been suffering (yes, it's been horrible) with the outside ambient temperature displayed inaccurately on the dashboard. It's very consistent but always off by three degrees high. This becomes a minor problem in the winter when the temperature gets to the 32 degree neighborhood. The temperature display might read 36 and I think that's safely far enough from 32 to not worry, but then I realize (most of the time) that it's really 33 out.
I looked up online how to fix this and discovered an incredibly useful phone app called Carista OBD2 (Android and iPhone). You must also purchase their little adaptor for $29.99. It plugs into your car's OBD (OnBoard Diagnostics) connector. The connector on my car is just a little lower and to the right of the hood release, easy to plug into once you know where it is.
I've used the app to fix the temperature display so that it is now accurate. There are a number of other customizations available but only two interested me. Now all four doors unlock when I click the remote or touch the door handle, and reverse only beeps once instead of continuous beeping.
Here's some information on cost and use.
As mentioned above, the adaptor is $29.99. Once you've downloaded the Carista OBD2 app, plugged in the OBD adaptor to your car, and turned on your car's ignition, the app will ask what kind of device you have. Select "Kiwi 3" (I discovered this by trial and error because the adaptor helpfully comes with no instructions). You're presented a screen with these three selections:
The first time you try to perform an action it takes you to a sub-screen informing you that you have a free month of service, and after that time you'll be charged $39.99 for one year. You don't enter any credit card information, just enter the password for your Apple account and they create a subscription for you. I don't know what happens on Android.
With an Apple Account it sends you a confirmation email saying that you've purchased a subscription with a one month free trial. You have one month to use the app for free. If you decide to cancel then go to Settings on your iPhone, click on your name at the top, click on Subscriptions, and the Carista subscription should appear in the list. Click on it and there'll be a new screen with a nice red "Cancel Subscription" button.
My initial thinking was to cancel once I had the customizations I wanted, but once the subscription is cancelled then I won't be able to modify any customizations. For example, my wife likes only the driver door to open upon one click or touch, and she might take over my car depending on what our next car is. Also, the "Service" page reports the exact pressure of all four tires, which is pretty useful.
One complaint: The Diagnose page takes a few minutes to initialize each and every time you use it. Customize takes about a minute, Service maybe 20 seconds. If you use the Diagnose page, then go to the Customize page, then try to return to the Diagnose page again, you'll again have to wait a few minutes for it to initialize. I don't think it's the app. I think the car probably responds slowly as it is queried for all it's settings.
But the Diagnose page isn't one you would likely use very often. It your car isn't misbehaving and doesn't seem to be having any problems then why diagnose? When I run it it presents a page that says "Faults detected: 0", and that's all.