Hi Happyglama,
Welcome to Apple Support Communities. We understand that you're having an issue with using Voice to text when using CarPlay. We'd like to help.
What happens when you try to use this feature? Are you enabling Siri first? Do you notice that this is affecting all parts of your CarPlay experience or just a specific app?
While we're waiting to hear those additional details, please give these steps a try:
If CarPlay doesn't work like you expect, learn what to do.
First, make sure that your country or region supports CarPlay and that your car supports CarPlay. If you're unsure if your car supports CarPlay, contact the vehicle manufacturer.
Make sure that your iPhone has the latest version of iOS. If your iPhone is updated to the latest version of iOS, follow these steps—checking CarPlay after each step:
1. Check your connection to your CarPlay stereo:
* If you have a wired connection, try connecting again with a different USB cable to a different USB port if you have one.
* If you have a wireless connection, make sure that Bluetooth is turned on on your iPhone under Settings > Bluetooth. Then go to Settings > Wi-Fi, and make sure that Wi-Fi is also turned on. Tap the CarPlay network, and check that Auto-Join is turned on.
2. If CarPlay doesn't activate automatically, look for the CarPlay logo on your car's display and select it.
3. Restart your iPhone and your car.
4. Make sure that Siri is on.
5. If your iPhone isn't detected by CarPlay, make sure that CarPlay isn't restricted. Go to Settings > Screen Time > Content & Privacy Restrictions. If Content & Privacy Restrictions is on, tap Allowed Apps, and make sure that CarPlay is enabled.
6. Go to Settings > General > CarPlay, tap your car, then tap Forget This Car. Then set up CarPlay again.
7. Make sure that your CarPlay stereo is using the latest firmware from the car manufacturer. Check your car's manual for more information.
The above is from If you need help with CarPlay - Apple Support.
Step 7 is pretty important since you’ve most likely updated your iPhone. The firmware of your CarPlay stereo may need updating too.
Let us know if that helps!
All the best.
