Hello tc21,
We understand you're having issues using Siri to reply to messages while driving. In this case, we'd recommend taking these related steps to try to solve this:
Confirm your device is updated and how the issue occurs:
- Make sure your updated to the latest iOS version available for your device: Update your iPhone or iPad - Apple Support
- Confirm if the issue occurs when the iPhone is locked and unlocked.
Is Automatically Send Messages enabled? Check with the following steps:
- Go to the Settings app.
- Tap on Siri & Search.
- Make sure 'Automatically Send Messages' is disabled here.
Download and test another Siri language:
- Go to the Settings app.
- Tap on Siri & Search.
- Tap on Language
- Select another language (similar to yours so you don't get lost in Settings app) For example, for English you could download and test the English UK or UK options.
Reboot and test
Make sure you've tested a good normal restart of your iPhone: Restart your iPhone - Apple Support
Should the issue continue to occur, then it would be best to contact Apple directly: Apple Support
They'll need to take it from here.
Wishing you well, take care.